PROBING IN INORGANIC-ORGANIC HYBRID
NEW DELHI- 110016, INDIA
LINEAR AND NONLINEAR OPTICAL EXCITON
PROBING IN INORGANIC-ORGANIC HYBRID
Doctor of Philosophy
NEW DELHI- 110016, INDIA
i
CERTIFICATE
This is to certify that the thesis entitled, “Linear and Nonlinear Optical Exciton Probing in
Inorganic-Organic Hybrid Semiconductors” being submitted by Mr. Mohammad Adnan,
to the Indian Institute of Technology Delhi, New Delhi, for the award of degree of Doctor of
Philosophy in Physics is a record of bonafide research work carried out by him under my
supervision and guidance. He has fulfilled the requirements for submission of the thesis, which
to the best of my knowledge has reached the requisite standard.
The material contained in the thesis has not been submitted in part or full to any other
University or Institute for the award of any degree or diploma.
Dr. G. Vijaya Prakash Professor Department of Physics Indian Institute of Technology Delhi New Delhi-110016 India
March 2021
ii
ACKNOWLEDGEMENTS
This thesis is an outcome of the efforts from many people who helped and supported to
carry out this work. I would like to sincerely thank to those people and institutions for making
this work possible. Pursuing this PhD has been a turning point in my life that happened with
the love and supports from them. First and foremost, I thank almighty GOD (Allah) to shower
his blessings for the successful completion of my thesis. I owe a deep sense of gratitude to my
parents Mr. Mohammad Naseem and Mrs. Shahidun Nisha for their constant love, support,
encouragement and for everything during this period. Their struggle during early days of my
life taught me some tough lessons of life. I am extremely thankful to my brothers Mr. Rehan,
Mr. Zeeshan, Mr. Izhan and sisters Ms. Tamanna and Ms. Fauzia to encouraging me to pursue
my passion towards research.
I express my sincere gratitude to Prof. Jeremy J. Baumberg, FRS, Nanophotonics
Centre, Cavendish Laboratory, University of Cambridge, UK for his valuable suggestions and
discussions throughout my PhD. I am very thankful to him for hosting me as a Newton Bhabha
fellow and providing all the required facilities during my stay at Cambridge.
I would like to thank our mentor and collaborator Prof. D. Narayana Rao, School of
Physics, University of Hyderabad for fruitful discussion and help regarding nonlinear
spectroscopy. I am grateful to him to always encourage and motivate and his curiosity
regarding data analysis.
I am highly indebted to Prof. Anurag Sharma (UFO co-ordinator) for his constant
support, help and motivation and providing essential laboratory facilities at Ultrafast Optics
(UFO) Lab.
I am highly indebted to Prof. Pankaj Srivastava and Prof. Santanu Ghosh, for providing
me Nanostech laboratory facilities.
I heartily thank Prof. Sumeet Mahajan, Institute for Life Sciences, University of
Southampton, UK for his kind support and making all the arrangements during my visit to
Southampton. It was really wonderful experience to spend quality times in the lab with him.
I would like to express my deep gratitude to my Scholar’s Research Committee (SRC)
members Prof. Joby Joseph (Dept. of Physics), Prof. Sunil Kumar (Dept. of Physics) and Prof.
Jacob Josemon (Dept. of Material Science, IIT Delhi) for their suggestions, inspiration,
iii
motivation and all needful support throughout my Ph.D. I especially acknowledge my former
H.O.Ds of Physics Department: Prof. B. R. Mehta, Prof. Anurag Sharma and present H.O.D.
Prof. Ratnamala Chatterjee, for all the help and support they provided during their tenure. My
sincere thanks to our lab collaborators, Prof. A. Ramanan, Department of Chemistry, IIT Delhi,
Prof. R. Nagarajan, Department of Chemistry, University of Delhi and Prof. A. Srinivas Rao,
Department of Physics, Delhi Technological University, New Delhi, India. My special thanks
to Prof. Dinesh Kabra, IIT Bombay for his motivation, moral support and guidance.
It was really thrilling and great learning experience to work at Nanophotonics
Laboratory, Ultrafast Optics Laboratory and Nanostech Laboratory and thanks to all the
members for their co-operation. My sincere thanks to all my seniors Dr. Mohini Gupta, Dr.
Udai Bhan Singh, Dr. Suman Shakya, Dr. Pawan Kumar Kanaujia, Dr. Pushpsen Satyarthi, Dr.
Debalaya Sarkar, Dr. Vinod Parmar, Dr. Sreekanth Maddaka, Dr. Parsawajit Kalita for their
constant support and co-operation. I am deeply thankful to my colleagues Mr. Harsh, Mr.
Preetam, Mr. Gulshan, Mr. Chandra Prakash Verma, Ms. Priyadarshini, Mr. Jitendra Nath
Acharyya and Mr. Kshetra Mohan Dehury, Mr. Waseem, Ms. Pariksha Malik for their co-
operation and work friendly environment. Also thanks to project trainees Ms. Angika Bulbul,
Mr. Ajay, Mr. Indraj, Mr. Monu, Mr. Vivekanand Tiwari, Mr. Addankani Satya Sai, Mr. Rohit
and Mr. Sourabh for their help in experimental and non-experimental works as and when
required. It was exhilarating to work at Naophotonics Centre, Cavendish Laboratory,
University of Cambridge, UK. I am very grateful to Felix, Femi, Sean, Sachin, Ibrahim, Joanna,
Thomas, Sascha, Haralds, Angus, Lisa, Tim and Timo for their co-operation. I am also thankful
to Steve and Adam for training on Dektak profilometer and XPS measurements respectively. I
extend my thanks to Jennie for all the paper works and making arrangements for my stay at
Cambridge, UK. I also thank Egle, Chris and Dennielle for all their helps.
I am grateful to all my friends from IITD, Mr. Hemojit, Mr. Sourav, Mr. Ankit Butola,
Mr. Vishal, Mr. Kashif, Mr. Habib, Mr. Gya Prasad, Mr. Sushant, Mr. Himanshu, Mr. Abhishek
for their help and precious company during the time away from the lab.
I pay my sincere thanks to Mrs. Pasupuleti Srilakshami for her endless love, supports
and blessings throughout my PhD. Whenever I needed, she always stood tall behind me as a
mother. I am always thankful to my best friends, Zeeshan, Vijaya Malhaar, Affan, Azhar,
Sonam, Meraj and Sai, for their constant encouragement and unconditional support forever. I
am obliged to Dr. Mohammad Tanveer for his support and valuable suggestions. They are the
persons who made me happy during a tough time of Ph.D. I owe my special gratitude to elder
iv
brother Dr. Sharique Nomani, Department of Urdu, Aligarh Muslim University, Aligarh for his
proper guidance throughout my career and shape my future.
I acknowledge DST-INSPIRE and CSIR for providing research fellowship and travel
grant to attend national/international conferences in India and Egypt. I would also like to thank
British Council UK and DST India for providing me funding for Newton Bhabha PhD
fellowship program to carry part of research work at Cavendish Laboratory, University of
Cambridge, UK. I also thank to German Research Foundation (DFG), Department of Science
and Technology (DST) and Lindau Committee to provide me great opportunity to attend the
69th Lindau Nobel Laureate Meeting held in Lindau, Germany. I would also like to thank FIST
(DST Govt. of India) UFO scheme and CRF of IIT Delhi for providing characterization
facilities. My personal thanks to Dr. S.M. Babu and Dr. Sivaji from DST for their unhesitant
help at DST.
Finally, I express my admiration and deepest gratitude to my thesis supervisor Prof. G.
Vijaya Prakash, for all the support and encouragement he gave me throughout the entire
journey. Without his motivational guidance and constant encouragement, I could not have
achieved this goal. I am really thankful to him for introducing me to the fascinating world of
Ultrafast Optics and Nanophotonics. Also, his constant guidance and efforts really helped me
to work at Cavendish Laboratory, University of Cambridge as a Newton Bhabha fellow. His
critical analysis and demonstration have taught me how to be an independent researcher. His
support and integral view on research laid a strong foundation of my research career. His care,
valuable suggestions, unwavering guidance, motivation and encouragement throughout my
work and above all his sacrifices for his own happiness have been vital for bringing this thesis
in the present form. From his inclination towards a philosophical approach, I have learned
about the importance of ethics in research as well as in life.
(Mohammad Adnan)
Hybrid materials, incorporating both organic and inorganic constituents into a single molecular
level composite, are emerging as effective and promising new materials due to the diverse, but
complementary properties of these different classes. The tailor-made molecular combination
of the attractive inorganic and organic features within a single molecular-scale composite can
be synergistically exploited to overcome the limitations of individual entities. Among various
hybrids, incorporation of suitable passive organic moieties into the active inorganic
semiconducting matrix are most interesting and well-studied hybrids. The thesis motive is to
demonstrate the influence of structure and laser-matter interactions on the strong room-
temperature optical exciton energies of the novel inorganic-organic (IO) hybrid
semiconducting hybrids. The synthesis and optical properties of varieties of IO hybrid
semiconductors are systematically explored with the key motivation to understand the room-
temperature exciton photoluminescence dynamic and static behaviour in the linear and
nonlinear excitation domains. Nonlinear optical probing with high intense Infrared ultrashort
pulses provide information of sample deeper depths and reveal several underlying structural
perturbations such as inter-layer distortions and intra-layer crumpling and also information
about new excited states and their relaxations. The study of transient absorption and time-
resolved photoluminescence studies highlight the excitation and de-activation mechanisms of
various excitons involved. The thesis also presents the laser-induced reversible phase
segregation effects and drastic effects of surface functionalization on quantum sized IO
structures. All these comprehensive studies of these novel metal-organic frameworks open new
avenues to explore fundamental aspects as well as novel and advanced optoelectronic
applications.
 
  ,                 
  , ,                    
                      
                      
            ,        
                    
       (IO)         
                     
 IO                      
                     
                        
                      
                 
                         
                      
                     
                   
                           
             
vi
1.2 Optical excitons in semiconductors 4
1.3 Hybrid semiconductors 6
processes in semiconductors 19
1.4.3 Time-resolved photoluminescence spectroscopy 24
1.5 Motivation and Objectives of the work 26
CHAPTER 2: 33-64
2.1 High intensity ultrafast laser beam lines and setup 33
2.2 Multi-functional Optical Microscope: Optical imaging and mapping 41
2.3 Two or multi-photon absorption induced photoluminescence
(2PA-PL or MPA-PL) setup 43
2.4 Ultrafast absorption ad reflection spectral dynamics from transient
pump-probe spectroscopy 44
photoluminescence spectroscopy setup 46
2.6.1 In-situ and time-resolved photoluminescence measurement setup 51
vii
2.7 Synthesis and Fabrication methodologies for IO hybrids 54
2.7.1 Conventional solution processing techniques 54
2.7.2 Synthesis of colloidal 3D IO hybrid nanoparticles 55
2.7.3 Organic iodide intercalation process into parent PbI2 57
2.7.4 Thin film fabrication: from thermal vapor deposition and Spin coating 58
2.8 Structural and physical characterization techniques 60
2.8.1 Glancing angle X-ray Diffraction (XRD) 60
2.8.2 Scanning Electron Microscopy (SEM) and Energy dispersive
X-ray spectroscopy (EDX) 61
CHAPTER 3: 65-85
diverse IO hybrid materials
3.2 Effect of 2D layered behavior and crystal packing based
on organic moiety conformation within MX2 semiconductor 69
3.3 Room-temperature optical exciton features of 2D layered IO hybrids 74
3.3.1 Study of optical excitons in structurally slightly different
Inorganic-Organic hybrids, MPEPI and CEPI 74
3.3.2 Structural phase flip related optical excitons in long alkylamine
based 2D IO hybrids 77
3.4 Optical exciton structural sensitivity from conventional high resolution
microscopy, high resolution PL imaging and spectral spatial mapping 79
3.5 Conclusion 84
CHAPTER 4: 86-113
Linear and nonlinear optical probing of various excitons and their PL dynamics in 2D
IO hybrid materials
4.1 Brief introduction 86
4.2 Linear and nonlinear optical properties of optical excitons in 2D IO hybrids 88
4.2.1 Linear optical excitons under conventional UV excitations 88
4.2.2 Nonlinear optical excitons under ultrafast intense 400 nm
viii
400 nm excitation (one-photon) 94
4.2.4 Nonlinear optical excitons under infrared excitations (two-photon) 98
4.2.5 Two-photon PL excitation spectra (2PA-PLE), origin of dark
exciton states and nonlinear absorption cross-sections 100
4.2.6 Two-photon exciton PL dynamics under ultrafast intense IR excitations 106
4.2.7 One and two-photon excited photoluminescence (1PA- and 2PA-PL)
spatial mapping and PL imaging analysis 107
4.3 Conclusion 112
CHAPTER 5: 114-133
Laser induced exciton switching behavior in long alkylamine based IO hybrid materials
5.1 Introduction 114
5.3 Methodology and experimental details 116
5.4 Results and discussion 117
5.4.1 Optical exciton features in long alkylammonium based IO hybrids 117
5.4.2 Laser induced exciton phase switching in long alkylammonium
based IO hybrids: one-photon induced (λexe= 400 nm) 119
5.4.3 Laser induced exciton phase switching in long alkylammonium
based IO hybrids: Two-photon induced (λexe= 800 nm) 121
5.4.4 One-photon and two-photon induced PL dynamics in
long alkylammonium based IO hybrids 123
5.4.5 Analysis of exciton phase flips and phase transition/stability
kinetics modelling 125
5.5 Conclusion 132
CHAPTER 6: 134-161
nanoparticles
ix
colloidal nanoparticles 139
nanoparticles 141
colloidal nanoparticles: Photoluminescence properties 143
6.6 Phase stability and reversibility studies in the surface functionalized
mixed halide CH3NH3Pb(BrxI1-x)3 colloidal nanoparticles 148
6.7 Growth and phase transitions/stability kinetic studies in the surface
functionalized mixed halide CH3NH3Pb(BrxI1-x)3 colloidal nanoparticles 154
6.8 Discussion 158
6.9 Conclusion 160
CHAPTER 7: 162-184
Study of surface and bulk recombination kinetics of 2D IO hybrid semiconductors under
linear and nonlinear femtosecond transient absorption analysis
7.1 Introduction 162
7.2 Charge carrier dynamics in linear excitation region (One-photon excitation) 166
7.3 Carrier temperatures from transient absorption data 171
7.4 Charge carrier dynamics in nonlinear excitation region
(Two-photon and three-photon excitations) 174
7.5 Conclusion 184
CHAPTER 8: 185-207
8.1 Conclusions 185
References 191-202
International/national Conferences and Presentations 205
Workshop Participation 205
List of Figures
Chapter 1: Introduction
Figure 1.1: The transition of electronic energy states of a semiconductor from discrete
molecules to Quantum Dots (QDs) and bulk crystals.
Figure 1.2: Basic representation of AMX3 and A2MX4 type structures, where A is the organic
moiety with NH3 termination, M is metal (Pb2+, Sn2+…) and X is halogen (I-, Br-
, Cl-…)
Figure 1.3: (a) Schematic representation of 2D alternative stacking of organic and inorganic
layers and corresponding multiple quantum wells structures based on the
inorganic organic bandgap energy levels (b,c) represent the schematic of exciton
formation and recombination processes in these IO hybrid semiconductors
Figure 1.4: Schematic representation of TEM00 Gaussian laser beam and the beam waist (ω0),
Rayleigh width and lengths after a lens
Figure 1.5: Systematic representation of various laser matter interaction phenomena occurring
at different intensity and time scales
Figure 1.6: Schematic energy level for linear absorption and recombination and various
nonlinear absorption processes such as two-photon absorption, excited state
absorption, exciton-exciton annihilation, free carrier absorption, Auger processes
in semiconductors
Figure 1.7: Schematic overview of ultrafast pump-probe experiment where a stronger pump
pulse (blue color) excites the sample and a weaker delayed probe pulse (red color)
monitors the optical absorption changes
Figure 1.8: (a) Schematic energy level diagram depicting pump probe process clearly
demonstrating ground state bleaching (GSB), stimulated emission (SE) and
excited state absorption (ESA) processes and corresponding transient absorption
spectra is shown in (b)
Figure 1.9: Mechanism of time resolved photoluminescence process when excited by a
Gaussian pulse (blue color). Emission pulses are detected at gate open interval
and PL decay is shown as thick solid line with circles representing the exponential
function
xi
Chapter 2: Fabrication and Characterization Techniques
Figure 2.1: (a) High intensity Ti: Sapphire femtosecond lasers in our lab (b) beam path is
shown in the figure which consist of three laser sources (i) 690-1040 nm, 120 fs,
84 MHz, 3 W (ii) 800 nm, 120 fs, 1 KHz, 4 W and (iii) 240-2700 nm, 120 fs, 1
KHz, 30-600 mW
Figure 2.2: Absorption and emission spectra of Ti: Sapphire crystal exhibiting broad
absorption and emission band region
Figure 2.3: Principle of chirped pulse amplification process for the generation of high intensity
ultrashort laser pulse
Figure 2.4: (a-d) various nonlinear processes for the generation of different output pulses
inside optical parametric amplifier
Figure 2.5: Electronic parts used in fs laser: (a) output pulse on the oscilloscope confirm the
regenerative amplification process (b) is the temperature controller unit and time
delay generator (c) Empower controller or power supply (d) is the temperature
sensor used to maintain the lab temperature around 21°C (e and f) a power meter
showing the power level of 800 nm, 1 KHz, 120 fs pulses from amplifier @
Ultrafast Optics Lab, IIT Delhi
Figure 2.6: (a) Autocorrelation process for measuring pulse duration and (b,c) photograph of
autocorrelator
Figure 2.7: Various experiments carried out using different femtosecond laser source @
Ultrafast Optics Lab, IIT Delhi
Figure 2.8: One-stop measurements of optical images, spectra, and spatial mappings (line
scans and intensity scans) for both PL, reflection and transmission of samples
using extensively modified optical microscope. (a) Photograph of modified
upright optical microscope (b) Schematic representation of modified PL
microscope equipped with different laser sources and attached with spectrometer
(c) contains bright field (BF), dark field (DF), photoluminescence (PL) spectra at
a given point. The intense green color PL images are shown under 365 nm and
400 nm excitations along with PL spatial mapping monitored at 515 nm for one
of the IO hybrid single crystal platelets (more details in Chapter 3 & 4).
Figure 2.9: Experimental setup for one-photon, two-photon and multi-photon induced
photoluminescence (MPA-PL) utilizing various laser sources (1) MaiTai (690-
1040 nm, 84 MHz, 120 fs, 3 W, fs1), (2) Spitfire (800 nm, 1 KHz, 120 fs, 4 W,
fs2) and (3) TOPAS (240-2700 nm, 1 KHz, 120 fs, 30 mW to 600 mW), (4) CW
laser 400 nm and (5) 400 nm from 800 nm of laser source fs1 (with BBO crystal).
The representative photograph of 1PA- and 2PA-PL spectra for one of the IO
hybrid thin film.
xii
Figure 2.10: Schematic ray diagram showing the experimental setup for transient pump-probe
spectroscopy and transient absorption spectra for one of the IO hybrid thin film
is shown as an example. λex: 350 nm, 120 fs, 1 KHz and probe: white light from
CaF2
Figure 2.11: Schematic diagram showing the experimental setup for time resolved
photoluminescence spectroscopy
Figure 2.12: Photograph of time resolved photoluminescence setup. (a) Decay kinetics in time
correlated single photon counting (TCSPC) mode and (b) upconversion mode
Figure 2.12.1: Principle of Time correlated single photon counting (TCSPC)
Figure 2.12.2: Schematic of up-conversion method: the infrared pulse at 800 nm (1) generates
SH pulse at 400 nm using a nonlinear BBO crystal. 800 nm gate pulse is delayed
by the optical delay line, whereas 400 nm is used to excite the sample. The
generated emission (ω2) is collected by a lens and focused into a nonlinear BBO
crystal together with the delayed gate pulse (ω1). The sum frequency signal
(ωupconversion = ω3 = ω1 + ω2) generated by mixing in the BBO crystal is coupled to
the monochromator and is recorded by the CCD detector.
Figure 2.13: Schematic of in-situ photoluminescence (PL) and transmission measurement
setup. Example data of (a) typical Image plot real time PL evolution monitoring,
(b) extracted spectra at different time and (c) Peak PL intensity plot with time
Figure 2.14: (a) The absorption/transmission/reflection spectrometer and the schematic ray
diagram along with a representative absorption spectrum is shown. (b) The
excitation and emission spectroflurometer and schematic diagram along with a
representative excitation and emission spectra are shown.
Figure 2.15: Flow chart describing inorganic-organic hybrid synthesis procedure
Figure 2.16: Flow chart describing the synthesis of inorganic-organic mixed halide colloidal
nanoparticles
Figure 2.17: Flow chart describing the intercalation process
Figure 2.18: (a) Photograph of Vacuum Technique (Model-12'' coating unit) from Hind High
Vacc. Thermal vapor deposition system (b) Schematic representation showing
inside view of the evacuated main chamber (c) schematic of spin coating process
for obtaining uniform thin film (d) photograph of a spin coater and (e) IO hybrid
thin films
xiii
Chapter 3: Synthesis, structural and optical properties of two-dimensional layered and
structurally diverse IO hybrid materials
Figure 3.1: Various chemical structures based on the different organic moieties group forming
different dimensionalities
Figure 3.2: Cyclic, alkyl-chain and substitution based cyclic organic moieties utilized in this
chapter
Figure 3.3: (a) & (b) Schematic crystal packing of MPEPI and CEPI showing layer separation
and Pb-I-Pb bond angle respectively. (Hydrogens are omitted for clarity) (From
Cambridge Crystallographic Data Centre (CCDC) CIF Nos. 916338 and 932654
for CEPI and MPEPI respectively)
Figure 3.4: (a) & (b) Schematic diagram showing terminal halide and right angled triangle
bonding configuration in both MPEPI and CEPI respectively
Figure 3.5: Schematic crystal packing of CHPI showing two-dimensional layered structures
with layer separation ~8.71 Å. (b) N…H-I terminal halide bonding configuration
of CHPI
Figure 3.6: (a) & (b) Schematic crystal packing of both phases of C12PI showing layer
separation and Pb-I-Pb bond angles. (Hydrogens are omitted for clarity)
Figure 3.7: Thin film Glancing angle XRD (GAXRD) of different organic moieties based
two-dimensional inorganic-organic hybrid structures such as MPEPI (brown),
CEPI (black), CHPI (red) and C12PI (blue). The planes are oriented along (00l)
and (2l 00) (l=1,2,3…) planes respectively
Figure 3.8: (a) Room-temperature optical absorption spectra of typical 2D IO hybrid
structures; CEPI (black) and MPEPI (red) and schematic energy level diagram
(top) depicting different peaks in the absorption spectra eg. charge transfer (CT),
band edge and excitons. (b) Photoluminescence spectra of CEPI and MPEPI
under 400 nm CW laser excitation (Power~5 mW)
Figure 3.9: Linear absorption and photoluminescence spectra of one of the two-dimensional
inorganic-organic hybrid CHPI thin film
Figure 3.10: Exciton absorption and PL spectra of phase-I and phase-II of the C12PI thin film.
Exciton absorption peak associated with phase-I (red) and phase-II (black) are
observed at 490 nm and 505 nm respectively. Linear absorption induced
photoluminescence are shown by downshifting along the y axis scale.
xiv
Figure 3.11: Optical images of CEPI single crystal platelet. (i) bright field (BF) image (ii) dark
field (DF) image and (iii-iv) photoluminescence (PL) images under 400 nm CW
and 400 nm femtosecond laser (84 MHz, 120 fs) excitations respectively
Figure 3.12: (A-i) Shows PL spectra of CEPI crystal when excited by 400 nm CW laser. The
spectra are deconvoluted into free-exciton (PLFE) at 512 nm, crumpled exciton
(PLCE) at 541 nm and defect induced emission (PLdef) at 585 nm. (ii-iv) PL crystal
spatial mapping of CEPI crystal under 400 nm CW excitation (at power < 1 mW),
where in each figure (ii-iv) correspond to free-exciton, crumpled-exciton and
defect-induced emission respectively, similarly (B) shows PL spectra and crystal
spatial mapping of CEPI under 400 nm fs1 laser excitation at P = 400 μW, I = 0.1
GW/cm2.
Figure 3.13: (i) CEPI PL image, (ii) PL spatial mapping at free-exciton (~ 512 nm) and (iii)
respective spectral horizontal line spectral domain scan at the middle of the
platelet. (iv) Normalized PL spectra extracted at various points on the platelet.
Being a single crystal platelet, the PL spectra to various positions of crystal
represent the thickness dependent PL which clearly indicate that different position
spectra show no exciton PL peak shift
Figure 3.14: Optical images of MPEPI single crystal platelet. (i) bright field (BF) image (ii)
dark field (DF) image and (iii-iv) photoluminescence (PL) images under 400 nm
CW and 400 nm fs1 laser (84 MHz, 120 fs) excitations respectively
Figure 3.15: (A-i) Shows PL spectra of MPEPI crystal when excited by 400 nm CW laser. The
spectra are deconvoluted into free-exciton (PLFE) at 503 nm, crumpled exciton
(PLCE) at 531 nm and defect induced emission (PLdef) at 560 nm. (ii-iv) PL crystal
spatial mapping of MPEPI crystal under 400 nm CW excitation (at power < 1
mW), where in each figure (ii-iv) correspond to free-exciton, crumpled-exciton
and defect-induced emission respectively, similarly (B) shows PL spectra and
crystal spatial mapping of MPEPI under 400 nm fs1 laser excitation at P = 400
μW, I = 0.1 GW/cm2
Figure 3.16: (i) MPEPI PL spatial mapping at free-exciton (~ 503 nm), (ii) respective spectral
horizontal line spectral domain scan at the middle of the platelet, (iii) Normalized
PL spectra extracted at various points on the platelet. (iv) Corresponding PL
image. Being a single crystal platelet, the PL spectra at two different positions of
crystal represent the thickness dependent two distinctly different excitons (Figure
3.16 (v)).
xv
Chapter 4: Linear and nonlinear optical probing of various excitons and their PL
dynamics in 2D IO hybrid materials
Figure 4.1: (a) Schematic crystal structural packing of 2D IO hybrid ((R-NH3)2PbI4 type),
where infinitely extended 2D monolayers of [PbI6] 4- octahedra are separated by
inter-digitized organic moiety layers and (b) represents schematic energy level
diagram showing various possible excitation and de-excitation mechanisms,
namely, linear absorption, one-photon (1PA) and two-photon (2PA) absorption
induced photoluminescence (PL) processes within inorganic conduction and
valance bands
Figure 4.2: Linear absorption and conventional photoluminescence (1PA-PL) spectra of CHPI
thin film (inset shows bright field (left) and PL images (right) of single crystal
platelets). Ex: 410 nm CW laser
Figure 4.3: (a) Intensity dependent photoluminescence spectra of CHPI thin film (b) is laser
excitation intensity dependent 1PA-PL peak intensity plot, λex=410 nm CW laser
Figure 4.4: (a) Bright field (BF) and (b) dark field (DF) images of CHPI crystal platelets using
optical microscope BX-51. (c,d) PL crystal images were recorded by exciting
with 365 nm and 480 nm Hg sources
Figure 4.5: shows PL spectral spatial mapping (at λmax=515 nm) and PL line scans in both X
and Y directions. Corresponding PL spectra is also shown. λex= 365 nm (from Hg
source).
Figure 4.6: (a,b) Intensity dependent photoluminescence spectra of CHPI thin film when
excited with 400 nm fs1 and fs2 lasers, corresponding to the intensities 0.08 to
2.5 GW/cm2 and 0.5 to 7.3 TW/cm2 respectively
Figure 4.7: (a,b): The peak PL intensity vs excitation intensity plots of one-photon excited
photoluminescence (1PA-PL) when excited with 400 nm fs1 and fs2 lasers
respectively
Figure 4.8: (a) Laser excitation intensity dependent time-resolved 1PA-PL dynamics for CHPI
thin film. Inset of (a) shows upconversion mode data at higher excitation intensity
(I=2.29 GW/cm2). (b) Exemplify the 1PA-PL life time fittings (black dark lines)
longer time scales (from Time Correlated Single Photon Counting (TCSPC),
range ~ 0-10 ns, resolution ~80 ps) and (c) short time scales (Up-conversion mode
detection, range 300 ps, resolution ~1 ps). This representative data is for the
excitation intensity I=2.29 GW/cm2 at 400 nm fs1 laser and monitored at 515 nm
Figure 4.9: Laser excitation intensity dependent time-resolved 1PA-PL dynamic fitting decay
constants (τ1, τ2 and τ3) vs excitation intensity (from Figure 4.8).
xvi
Figure 4.10: 1PA-PL spectra of CHPI thin film excited by 400 nm fs1 and fs2 lasers and 2PA-
PL spectra excited by 800 nm fs1 and fs2 lasers.
Figure 4.11: (a) NIR Excitation wavelength dependent 2PA-PL spectra from 780-1000 nm at
fixed excitation intensity 4 GW/cm2 from fs1 laser. Inset shows the plot of 2PA-
PL peak position shift with the tuning of excitation wavelength (PLE). (b) 2PA-
PL spectra (in frequency doubled scale). The conventional excitation spectra
(1PA-PLE) and 1PA- and 2PA-PL spectra are also shown in shaded colors for
comparison.
Figure 4.12: Estimated two-photon absorption (2PA) cross sections (η2σ2) for different NIR
excitation wavelengths. The data was monitored at 2PA-PL peak, 532 nm.
Figure 4.13: (a) shows the excitation intensity dependent 2PA-PL spectra, excited with 800
nm fs1 laser. The inset shows the plot of 2PA-PL peak shift with the incident laser
intensity. (b) plot of 2PA-PL peak intensity against incident laser intensity. λex:
800 nm, fs1 laser
Figure 4.14: Low intensity (~0.9 to 22x1012 W/cm2) excitation (a) shows the lower excitation
intensity dependent 2PA-PL spectra, excited with 800 nm fs2 laser. (b) Plot of
2PA-PL peak intensity against incident laser intensity. Similarly, (c) and (d) are
for high excitation intensities ~30 to 614x1012 W/cm2. Figure (c) inset contains
the peak shift (from 532 nm @ 1012 W/cm2) with respect to incident intensity.
Shaded region in Figure (d) is same as in Figure b. λex: 800 nm, fs2 laser
Figure 4.15: Open aperture Z-scan experimental setup. Open aperture Z-scan data for CHPI
thin film, the sample was excited by using 800 nm (>75 fs, 1 KHz) at excitation
intensity 1.6x1012 W/cm2 (@ experiments performed at School of Physics,
University of Hyderabad).
Figure 4.16: (a) Excitation intensity dependent time-resolved 2PA-PL dynamics for CHPI
film. Inset shows extracted lifetimes vs incident laser intensities. (b) shows the
excitation wavelength dependent time-resolved 2PA-PL dynamics. Inset shows
extracted lifetimes vs excitation wavelength. Excitation intensity was fixed at 3
GW/cm2 from fs1 laser
Figure 4.17: (a) 1PA-PL and (b) 2PA-PL spectra of CHPI single crystal platelet. The spectra
are deconvoluted into free-exciton (PLFE), crumpled exciton (PLCE) and defect
induced emission (PLdef). The respective peak maxima intensity spatial mappings
of crystals are shown. Respective PL images are shown as inset of (a) and (b)
respectively. The excitation wavelengths for 1PA-PL and 2PA-PL are 400 and
800 nm from fs1 laser respectively.
xvii
Figure 4.18: (A) 1PA-PL (400 nm, fs1) and 2PA-PL (800 nm, fs1) spatial PL peak intensity
mappings of CHPI single crystal platelet. (B) Spectral resolved horizontal line
scan at the middle of the crystal. (C) Normalized 1PA and 2PA-PL spectra
extracted at various points on the single crystal platelet (from Figure B). Having
irregular crystal surfaces, the PL spectra at various positions can be visualized as
the PL collection from varied depths/thickness. The observed peak shift in both
kinds of PL with respect to varied thickness/depth is only about 2-3 nm, while the
peak difference between 1PA and 2PA-PL is as large as ~17 nm.
Figure 4.19: (a) 2PA-PL spectral mapping of CEPI single crystal platelet. The spectral
intensity mapping at free-exciton (PLFE~512 nm), crumpled exciton (PLCE~541
nm) and defect induced emission (PLdef~585 nm) is demonstrated. (b) 2PA-PL
spectral mapping of MPEPI single crystal platelet. The spectral intensity mapping
at free-exciton (PLFE~503 nm), crumpled exciton (PLCE~531 nm) and defect
induced emission (PLdef~560 nm) is demonstrated. The excitation wavelength is
800 from fs1 laser
Figure 4.20: (a-e) Two-photon excited time scan spectra of CHPI thin film at different laser
power 60, 70, 80, 90 and 100 mW (~ I= 4.6 to 7.7 GW/cm2) to check the stability
of the sample degradation. Ex: 800 nm fs1 laser. (f) Plot of PL intensity with time
monitored at PL wavelength ~532 nm.
Chapter 5: Laser-based hybrid fabrication of silicon microstructures
Figure 5.1: Schematic energy level diagram for (a) phase-I and (c) phase-II showing various
optical processes: linear absorption, one-photon (1PA) and two-photon (2PA)
absorption induced photoluminescence (PL) processes within lowest inorganic
(PbI4 2- network) bandgap. (b) Schematic crystal packing of (C12H25NH3)2PbI4
(C12PI) phases, wherein the Pb-I-Pb extended network Pb-I-Pb bond angle
variations are projected
Figure 5.2: Exciton absorption and photoluminescence (PL) spectra of phase-I and phase-II of
C12PI thin film. The linear (one-photon induced PL, 1PA-PL) and nonlinear
(two-photon induced PL, 2PA-PL) excited PL are shown by downshifting along
y-axis scale. The Phase-II (red) and Phase-I (blue) contributions are indicated
with dotted lines and double headed arrows
Figure 5.3: Laser-induced one-photon excited PL (1PA-PL) dynamic changes of C12PI: (a1,
b1, c1) show the time vs PL spectral mapping and phase switching behaviour
when excited with 400 nm CW, fs1 and fs2 lasers. Corresponding spectra are
depicted in Figures (a2-c2). Phase-II and phase-I PL at 517 nm and 496 nm are
marked with dotted lines as II and I.
xviii
Figure 5.4: Laser-induced two-photon excited PL (2PA-PL) dynamic changes of C12PI. (a1
and b1) shows the time vs PL spectral mappings when excited with 800 nm fs1
and fs2 lasers respectively. Phase-II and phase-I PL peaks are marked as II and I.
Corresponding spectra are shown in Figures (a2 and b2).
Figure 5.5: (a,b) laser excitation intensity dependent time-resolved 1PA-PL and 2PA-PL
dynamics for C12PI thin film. For 1PA-PL, λex= 400 nm (fs1 laser) and monitored
at 517 nm and for 2PA-PL, λex= 800 nm (fs1 laser) and monitored at 525 nm
Figure.5.6: (a) Laser intensity-dependent 1PA-PL exciton lifetimes of C12PI thin film
monitored at 517 nm (Phase-II) (λex=400 nm, fs1 laser). (b) Laser intensity
dependent 2PA-PL exciton lifetimes of C12PI thin film monitored at 525 nm
(Phase-II) (λex=800 nm, fs1 laser).
Figure 5.7: One-photon induced phase flip: (a, b, c) initial and final time PL spectra when
excited by 400 nm CW, fs1 and fs2 lasers. (d, e, f) represents PL peak intensities
plotted along with laser exposure time. Dotted line curves are obtained from the
JMAK model fits using Eq. (5.1).
Figure5.8: Two-photon induced phase flip: (a, b) initial and final time PL spectra when excited
by 800 nm fs1 and fs2 lasers. (c, d) represents PL peak intensities plotted along
with laser exposure time. Dotted line curves are obtained from the JMAK model
fits using Eq. (5.1).
Chapter 6: Laser induced phase stabilities in mixed halide CH3NH3Pb(BrxI1-x)3 colloidal
nanoparticles
Figure 6.1: (A) Ambient (Bright field) and photoluminescence (PL) camera images of C1PBr,
C1PBr0.5I0.5 and C1PI nanoparticle colloidal solutions along with respective PL
spectra (λex= 405 nm). (B) Schematic energy level representation of C1PI
(CH3NH3PbI3) and C1PBr (CH3NH3PbBr3).
Figure 6.2: Photoluminescence spectra of (a) C1PBr, (b) C1PBr0.5I0.5 and (c) C1PI
nanoparticles colloidal solutions (λex=405 nm, CW laser at power=30 mW). Inset
shows the PL pictures of colloidal solutions when exposed to 405 nm laser light,
(with filter ALP 425 nm). (d) shows the absorption spectra of mentioned colloidal
nanoparticle solutions along with their respective pictures of solutions under
ambient light. (e) Photoluminescence spectra of 2D layered (C8H17NH3)2PbBr4
(C8PBr) (Ex: 320 nm, Xe lamp) and (C8H17NH3)2PbI4 (C8PI) (Ex: 405 nm, Diode
laser).
xix
Figure 6.3: (A) and (B) are representative TEM images and respective particle size distribution
of C1PBr, C1PBr0.5I0.5 and C1PI nanoparticles. (C) XRD patterns of C1PBr and
C1PI nanoparticles, (D) XRD patterns of C1PBr0.5I0.5 mixed halide nanoparticles
of bare and surface functionalized with C8 halide (C8Cl, C8Br and C8I)
Figure 6.4: Energy dispersive X-ray spectroscopy (EDX) analysis of agglomerated mixed
halide C1PBr0.5I0.5 nanoparticles (bare). (a) Mixed EDX elemental mapping and
individual elemental maps of (b) Lead (Pb), (c) Bromine (Br), (d) Iodine (I), and
(e) is the full EDX spectrum.
Figure: 6.5. Real-time evolution of photoluminescence (PL) spectral mapping against laser
exposure times for C1PBr0.5I0.5 nanoparticle colloidal solutions. PL spectra-Time
intensity maps are for (a) bare and functionalized with (b) C8Cl, (b) C8Br and (c)
C8I, C1PBr0.5I0.5 nanoparticles respectively. Right side images are corresponding
PL camera images taken at various intervals of exposure times. The PL spectra of
C1PBr (green color shaded) and C1PI (red color shaded) are also shown for
comparison. The PL spectra and images are recorded with a 405 nm CW laser
(Power= 30 mW).
Figure 6.6: (A) Photoluminescence (PL) spectra of bare and C8Cl, C8Br, C8I ligand
functionalized C1PBr0.5I0.5 nanoparticles recorded at (i) initial and (ii) after 10
min of continuous laser exposure with 405 nm CW laser. PL spectra of C1PBr
and C1PI are also shown in green and red shaded colors for comparison. (B) PL
peak intensities for various emission peaks from the PL spectra (Fig. 6.6A)
against laser exposure time. (C) The mixed-phase PL peak position variation with
exposure time for bare and surface-functionalized nanoparticles.
Figure 6.7: Time scan photoluminescence deconvoluted spectra (a) shows the time spectral
image of C1PBr0.5I0.5 mixed halide nanoparticles functionalized with C8Br when
excited with 405 nm CW laser (power=30 mW). The experiment was performed
for a longer duration of 1070 sec. The graphs b-d show the deconvoluted spectra
at 80 sec, 200 sec and 1070 sec, respectively, which indicate that how the
intermediate peak at 693 nm is getting stabilized with elapse of time.
Figure 6.8: (a) Real-time prolonged (>50 min) laser exposure PL spectral mapping of C8Br
functionalized C1PBr0.5I0.5 nanoparticle colloidal solutions and (b) corresponding
PL peak intensities of Br-rich sites (548 nm), mixed state (693 nm) and I-rich
(753 nm) sites against laser exposure time.
Figure 6.9: PL spectral reversibility of C8Br functionalized C1PBr0.5I0.5 mixed halide
nanoparticles. (a) Laser-induced real-time PL spectral variation mapping of C8Br
functionalized C1PBr0.5I0.5 nanoparticle colloidal solutions, where the laser
exposure was switched-OFF for 30 min during unaltered experimental conditions.
(b) Corresponding PL peak intensities of various PL peak positions against time.
xx
Figure 6.10: Effect of low and high powers of laser exposure on C8Br functionalized
C1PBr0.5I0.5 mixed halide nanoparticles. (a) Time vs. PL spectral mapping and (b)
PL intensities of respective peak positions of C1PBr (548 nm), mixed state (693
nm), and C1PI (753 nm) contributions for continuous exposure of laser. Here the
data is recorded for low and high laser powers, 5 mW and 30 mW, respectively.
It is evident that the phase segregation dynamics are similar in both high and low
laser powers exposure, except the variation in their intensities and relative time
scales for emerging of intermediate peak.
Figure 6.11: Laser-induced real-time PL spectral variation mapping of (a) bare, (b) C8I
functionalized, and (c) C8Br functionalized C1PI nanoparticle colloidal solutions.
PL peak position variation with time are indicated in gray color dots. PL spectra
of C1PBr and C1PI are also shown in green and red shaded colors for comparison.
(d & e) PL peak intensities against laser exposure time for (d) bare and C8I
functionalized C1PI nanoparticles and (e) for C8Br functionalized C1PI
nanoparticles.
Figure 6.12: Laser-induced real-time PL spectral variation mapping of C8Br functionalized
C1PI colloidal nanoparticles, where the laser exposure was switched OFF for 30
min during the unaltered experimental conditions.
Figure 6.13: Effect of low and high power laser exposure on C8Br functionalized C1PI
nanoparticles. Time vs PL spectral mapping for (a) at 5 mW and (b) at 30 mW,
respectively. It is evident that the phase segregation dynamics are similar in both
low and high laser powers exposure, except the variation in their intensities and
relative time scales.
Figure 6.14: PL peak intensity variation during prolonged UV laser exposure time (From
Figures 6.6 and 6.11) along with JMAK fittings from Eq 6.1. (a-c) graphs are for
bare and surface functionalized (with C8I and C8Br) colloidal C1PI nanoparticle
solutions respectively. (d-g) are for bare and functionalized (with C8Cl, C8Br and
C8I) C1PBr0.5I0.5 colloidal nanoparticle solutions. The black lines represent the
theoretical fits of the JMAK expression (Eq 6.1).
Chapter 7: Study of surface and bulk recombination kinetics of 2D IO hybrid
semiconductors under linear and nonlinear femtosecond transient
absorption analysis
Figure 7.1: Typical layout of non-degenerate fs-TAS setup with pump pulses from OPA (300-
2700 nm, 1 KHz, 120 fs). The weak broad band probe (~400-1000 nm) is
generated by focusing µW powers of 800 nm light into CaF2 crystal.
xxi
Figure 7.2: (A) Schematic energy level diagram depicting pump probe process clearly
demonstrating ground state bleaching (GSB), stimulated emission (SE) and
excited state absorption (ESA) and photo-induced absorption (PIA) processes.
(B) Example of difference absorption along with steady-state absorption and
photoluminescence spectra. Blue color pulse is the excitation pulse.
Figure 7.3: (a) One-photon excited transient absorption spectral mapping pumped at 350 nm
with an initial carrier concentration N0=14.26x1017 cm-3 (F=26.89 uJ/cm2) (b)
Transient absorption spectra at different pump-probe time delays 0.1-4.7 ps (c)
Transient decay kinetics of various regions 490 nm (Photo-induced absorption
(PIA1/excited state absorption, ESA), 510 nm (ground state bleaching, GSB) and
522 nm (photo-induced absorption, PIA2) and their fitted lifetimes values are
shown.
Figure 7.4: Fluence dependent transient absorption spectral mapping pumped at 350 nm (1PA)
at different fluence values viz 4.2, 8.4, 16.9, 21.2 and 26.8 uJ/cm2.
Figure 7.5: (a) Fluence dependent zero delay transient absorption spectra (b) plot of bleach
intensity (~510 nm) with fluence shows linear dependency
Figure 7.6: Fluence dependent transient dynamics of (a) PIA1/ESA at 490 nm, (b) GSB at
510 nm and (c) PIA2 at 522 nm in CHPI thin film. Ex: 350 nm, 1 KHz, 120 fs.
Fluences: 4.2, 8.4, 16.9, 21.2 and 26.8 uJ/cm2
Figure 7.7: (a) Normalized transient absorption (TA) spectra of CHPI thin film, pumped at
350 nm, with an initial average carrier density of N0=14.26x1017 cm-3 over the
illuminated area (b) Change in photo-excited carrier temperatures against time
delay for different fluences
Figure 7.8: (a) Normalized negative transient kinetics of the ground state bleaching region at
510 nm with increasing initial carrier density (b) Reciprocal of kinetic traces
shown in (a) which is normalized at the maximum ground state bleach signal
(minimum ΔA−1). Ex: 350 nm, 1 KHz, 120 fs.
Figure 7.9: (a) Two-photon excited transient absorption spectral mapping pumped at 800 nm
with an initial carrier concentration N0=11.4x1018 cm-3 (F=426.4 uJ/cm2) (b)
Transient absorption spectra at different pump-probe time delays 0.1-4.6 ps (c)
Transient decay kinetics of various regions 490 nm (PIA1/ ESA), 513 nm (ground
state bleaching, GSB) and 525 nm (PIA2) and their fitted lifetimes values are
shown.
Figure 7.10: Fluence dependent transient absorption spectral mapping pumped at 800 nm
(2PA) at different fluence values viz 284.3, 348.2, 397.9 and 426.4 uJ/cm2.
Figure 7.11: (a) Fluence dependent zero delay transient absorption spectra (b) plot of bleach
intensity (~513 nm) with fluence. Ex: 800 nm, 1 KHz, 120 fs
xxii
Figure 7.12: Fluence dependent transient dynamics of (a) PIA1 at 490 nm, (b) GSB at 513 nm
and (c) PIA2 at 525 nm in CHPI thin film. Ex: 800 nm, 1 KHz, 120 fs. Fluences:
284.2, 348.2, 397.9 and 426.3 uJ/cm2.
Figure 7.13: (a) Kinetic profiles of 513 nm bleach recovery at various excitation densities.
Traces are normalized to the maximum bleach signal at each excitation energy
density. (b) Reciprocal of kinetic traces shown in (a). Solid lines are linear fits to
the second order rate equation n0/nt-1=kn0t, at various excitation densities where
kn0 is slope, n0 and k are initial carrier density and second order recombination
rate constant. Ex: 800 nm, 1 KHz, 120 fs.
Figure 7.14: (a) Three-photon excited transient absorption spectral mapping pumped at 1020
nm with an initial carrier concentration N0=7.78x1019 cm-3 (F=2264.6 uJ/cm2) (b)
Transient absorption spectra at different pump-probe time delays 0.1-2.4 ps (c)
Transient decay kinetics of various regions 485 nm (PIA1/ ESA), 510 nm (ground
state bleaching, GSB) and 525 nm (photo-induced absorption, PIA2) and their
fitted lifetimes values are shown.
Figure 7.15: Fluence dependent three-photon transient absorption spectral mapping pumped
at 1020 nm (3PA) at different fluence values viz 1415.4, 1840, 2052.3 and 2264.6
uJ/cm2.
Figure 7.16: (a) Fluence dependent zero delay transient absorption spectra (b) plot of bleach
intensity (~510 nm) with fluence. Ex: 1020 nm, 1 KHz, 120 fs
Figure 7.17: Fluence dependent transient dynamics of (a) PIA1/ESA at 485 nm, (b) GSB at
510 nm and (c) PIA2 at 525 nm in CHPI thin film. Ex: 1020 nm, 1 KHz, 120 fs.
Fluences: 1415.4, 1840, 2052.3 and 2264.6 uJ/cm2.
Figure 7.18: (a) The normalized kinetic profiles of 510 nm ground state bleaching region at
various excitation fluences. (b) Reciprocal of kinetic traces shown in (a) Solid
lines are linear fits to the second order rate equation n0/nt-1=kn0t, at various
excitation densities where kn0 is slope, n0 and k are initial carrier density and
second order recombination rate constant. Ex: 1020 nm, 1 KHz, 120 fs
Figure 7.19: (a) Zero delay TA spectra under excitation at 350 nm, 800 nm and 1020 nm (b)
comparative ground state bleaching carrier lifetimes under linear and nonlinear
excitations (c) Normalized transient kinetics recorded at bleach region for three
different excitation wavelengths (d) Lifetimes at different excitations
xxiii
List of Tables
Table 3.1: The empirical names and chemical formula of the synthesized IO-hybrids.
Table 5.1: Fitting parameters of JMAK model, for C12PI Phase-I and Phase-II under linear
one-photon and nonlinear two-photon induced photoluminescence
Table 6.1: JMAK model parameters for (i) C1PI, bare and surface functionalized with C8I and
C8Br colloidal nanoparticle solutions and (ii) for C1PBr0.5I0.5 bare and C8Cl,
C8Br and C8I surface functionalized colloidal nanoparticles.
Table 7.1: Carrier relaxation lifetimes (in ps) of ground state bleach region at 510 nm and
excited state absorption/photo-induced absorption regions at 490 nm and 522 nm
Table 7.2: Carrier relaxation lifetimes (in ps) of ground state bleach region at 513 nm and
photo-induced absorption regions at 490 nm and 525 nm under 800 nm two-
photon excitation
Table 7.3: Carrier relaxation lifetimes (in ps) of ground state bleach region at 510 nm and
photo-induced absorption/excited state absorption regions at 485 nm under 1020
nm three-photon excitation
C1I
BF
OPA
Super continuum generation
Thesis final_Mohammad Adnan.pdf
Linear and nonlinear optical probing of various excitons and their PL dynamics in 2D IO hybrid semiconductors
(i) Papers Published in JCR journals