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Development of Ln 3+-doped glasses and nano -glass ceramics for photonic and
optical sensor applications
Prof. C. K. JAYASANKARDepartment of Physics, Sri Venkateswara University,
Tirupati – 517 502, INDIA ,Email: [email protected]
Indo-French Workshop on Glasses and Glass-ceramics, 6-8 June 2012, Lille, France
2
ACTIVITIES OF OUR RESEARCH GROUP AT SVU
Basic research on Ln 3+: glasses and glass-ceramics(QUANTIFICATION OF OPTICAL PROPERTIES)
Development of Laser Quality Glasses
NanocrystallineLn3+:garnets,niobates andNano-glass-ceramics
Ultrashort pulse laserwaveguide inscriptionin glasses (Photonicchips)
Luminescence propertiesof lanthanide Ions dopedglasses under pressure
OUR RESEARCHACTIVITIES
3
OBJECTIVES To select and prepare various optical quality glasses and
glass-ceramics undoped (Passive) and doped (Active)with Ln 3+ ions.
To characterize and optimize these glasses and glass-ceramics and active ion concentrations by conventionalspectroscopic techniques (absorption, emission, decay,etc., measurements) and to provide quantitative opticalproperties.
To supply consistent quality glasses glass-ceramics forthe development of photonic devices.
To write waveguides and to create the modifications ofelemental distribution in the glasses using high energyultrafast laser pulses.
4
IMPORTANCE OF Ln3+ IONS
Applications
Solid state lasers
Phosphors
Optical fiber amplifiers
Optical storage materials
Light converters
Sensors
Acousto -optic modifiers
Planar waveguides, etc.
Science4fn - electrons shielded by 5s 2
and 5p 6 electrons and so:
Similar patterns in any ligandenvironment (all materials)
Several excited states, suitable for optical pumping.
Emit narrow line, monochromatic light and have long decay lifetimes.
Luminescence in all spectral ranges
5
Cr3+ : 1s2 2s22p6 3s2 3p6 3d3
Nd3+ : 1s2 2s22p6 3s2 3p6 3d10 4s2 4p6 4d10 4f3 5s25p6
Ytterbium
Lutetium
CeriumPraseodymium
Neodymium
Promethium
SamariumThulium
DysprosiumHolmium
Erbium
LANTHANIDES
Condensed Matter
Physics
LANTHANIDES
AtomicPhysics
Material Science
Communication
Industrial Applications
Imaging
MedicalScienceBiology
Plasma Physics
Astrophysics
Particle Physics
Rare Earth Centric Applications
8
Interactions seen by 4f n-electrons
• Coulomb f-f
• Spin-orbit interaction
• Crystal-field interaction with environment
4fn-electrons shielded by 5s 2 and 5p 6 electrons so:
• Sharp lines
• Long lifetimes
• Many ions to choose from 4f-series
• Similar patterns in all materials
So ideal for laser, photonic and phosphorapplications
4fn ENERGY LEVELS
9
SL
MJ
4f
COLOUMB SPIN-ORBIT CRYSTAL-FIELD
The measured shifts of each level as well as their splitting c anprovide the data necessary for probing the Coulomb, spin-or bit andcrystal-field interactions which are prerequisite for the design of anyoptical devices.
4fn ENERGY LEVELS : LIFTING OF DEGENRACY/ INTERACTIONS
10
VARIATION WITH BOND NATURE
Energy (cm -1)
Intensi
ty
∆∆∆∆νννν ββββR
)'',(28
4
)'',(
sec
JJA
effcn
PJJ
tioncrossemissionStimulated
ΨΨ∆
=ΨΨ
−
λπ
λσ
Ligand atomLn3+
νννν
∆ν∆ν∆ν∆ν = FWHM
ββββR = Branching ratio
11Energy (cm -1)
Stark SplittingIntensity
In order to improve emissioncross-section and lifetimes,the addition of variousnetwork formers and thevariation of chemicalcompositions are to beperformed, which couldchange the asymmetry of Ln 3+
and the covalence betweenLn3+ and ligand.
VARIATION WITH LIGAND ENVIRONMENT
12
Partial energy level structure of Ln3+ ions
13
ADVANTAGES OF GLASSES
Glass composition over a wide range
Disordered environment
Ease of fabrication and less expensive
Excellent homogenous and low birefringence
Good coupling to broad band sources such as flash lamps
High energy storage density
Prepare different shapes and sizes including fibers
Possibility of producing large active laser media with good
optical quality
14
EXPERIMENTAL TECHNIQUES
Glasses:
Phosphates
Silicates
Tellurites Oxyfluorides
Method: Melt quenching technique
Temperature: 1050-1500 oC
Annealing : 350 - 500 oC
Physical properties:
Density: Archimede’s principle
Refractive index: Abbe refractometer
Light source: Sodium vapour lamp (589.3nm)
1510 20 30 40 50 60 70 80
Powder X-ray difraction patern of typical glass
Glass
Inte
nsi
ty (
arb.
uni
ts)
2θ
GLASS PREPARATION
Melting at 850 – 1400 ºC
Annealing at ~350 ºC
Weight ~ 8 to 50 g
16
Ln3+-doped glasses
40 mm x 50 mm x 10 mm
150 mm long and 10 mm dia
Shadow images
Nd3+:Phosphate laser glass(prepared at SVU) Reference glass
Laser tomography is a way to observe micron or sub-micron size features byusing a laser beam to scan the substance. The laser beam is not only verystrong but also narrow, feeble scattering images can be detected using aphotographic camera, even if they cannot be seen with an opticalmicroscope.
MICRO DEFECT MEASUREMENT OF THE Nd3+:PHOSPHATE GLASS BY USING LASER TOMOGRAPHY.
Nd3+:Phosphate laser glass(prepared at SVU) Reference glass
Birefringence of the other Nd3+:glass with inclusions and damages
Birefringence of our Nd3+:phospahte glasses with minimum inclusions and damages
Birefringence , or double refraction , is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials.
20
PROPERTIES THAT ARE TO BE OPTIMIZED
Optical
Refractive Index
Non-linear refractive Index
Abbe number
Temp-coeff. Refract. Index
Temp-coeff. Optical path
Laser
Emission cross-section (IR)
Saturation fluence
Radiative lifetime (micro sec.)
Judd-Ofelt radiative lifetime
Judd-Ofelt parameters
Emission band width
Conc. quenching factor
Fluorescence peak
Thermal
Thermal conductivity
Thermal diffusivity
Specific heat
Coeff. Thermal expansion
Glass transition temperature
Mechanical
Density
Poisson’s ratio
Fracture toughness
Hardness
Young’s modulus
210
5
10
15
20
25
30
Ene
rgy
(103 c
m-1)
4I9/2
4I11/2
4I13/2
4I15/2
4F3/2
4F5/2
2H9/2
4F7/2
4S3/2
4F9/2
2H11/2
4G5/2
2G7/2
4G7/2
2G9/2
4G9/2,11/2
2P1/2
2D5/2
4D3/2
4D5/2
2I11/2
4D1/2
2D3/2
2P3/2
Nd3+-doped phosphate laser glasses
7000 8000 9000 10000 11000
0.0
0.5
1.0
1.5
2.0
2.0
1.0
0.1
PKMAN
Wavenumber (cm -1)
Nor
mal
ised
Inte
nsity
(arb
. uni
ts) λλλλexc=355 nm
4I9/2
4I11/2
4I13/2
4F3/2
(a) PKMAFN, (b) PKSAFN and (c) PKBAFN
P2O5K2O
Al 2O3BaO
x Nd 2O3
0 5 0 0 1 0 0 0 1 5 0 0
0 .0 1
0 .1
1
P K B A N
(c )
(b )
(a )N
orm
aliz
ed In
tens
ity
T im e ( µµµµ s )
(a ) = 0 .1 m o l%(b ) = 1 .0 m o l%(c ) = 2 .0 m o l%
NR
22
Decay curves with IH model fit
−−−−−−−−
====3/StQ
τ
t
eI(0)I(t)
0 1000 2000 3000 4000 5000
0.01
0.1
1
S=10
S=8
S=6
Nor
mal
ised
inte
nsity
(ar
b. u
nit)
Time (µµµµsec)
dipole-dipole
dipole-q.pole
q. pole-q.pole
Q = energy transfer parameter
CA = Acceptor concentration
CDA = Donar- Acceptor interaction parameter
[ ] SSDAA C
SCQ
3)(3
13
4
−Γ= π
ENERGY TRANSFER:NON-EXPONENTIAL DECAY ANALYSIS
S=6, dipole-dipole
S=8, dipole-q.pole
S=10, q. pole-q.pole
23
Our Results Versus Commercial Laser Glasses
S.No. Parameter Range(Our results)
LHG-80 LHG-8 LG-770 LG-750
1 Ω2 4.24 - 9.23 3.6 4.4 4.3 4.6
2 Ω4 2.86 - 8.28 5.0 5.1 5.0 4.8
3 Ω6 4.06 - 8.74 5.5 5.6 5.6 5.6
4 Ω4/Ω6 0.59 - 1.08 0.91 0.91 0.89 0.86
5 τ 491 - 211 327 351 349 367
6 λλλλp 1051.4 - 1054.8 1054 1053 1053 1053.5
7 ∆λλλλeff 23.5 - 30.7 23.9 26.5 25.4 25.3
8 σ(λp) 2.45 - 6.48 4.2 3.6 3.9 3.7
9 R0 6.8 - 11.7 6.52 6.38 4.1
24
Our Results Versus Commercial Laser Glasses
0
5
10
15
20
25
30
35
40
∆λeff, nm
σ(λp), x10-20 cm2
LG-750LG-770LHG-8LHG-80PKSAN10PKMAN10PKBAN10
Par
amet
ers
PK
MA
N
PK
MA
FN
PK
MA
BF
N
PK
MF
AN
PK
FM
AN
LHG
-80
LHG
-8
LG-7
70
LH-7
50
0
50
100
150
200
250
300
350
400
450
500
550
Rad
iativ
e Li
fetim
e (µ
s)
25
COMPARISON OF σ , n2 and σ/n2 for Nd 3+:LASER GASSES
Parameter Silicate Q88 Kigre
Phosphate LHG-8 Hoya
Fluoro-phosphate PKFSAN10 India
σ x10-20
cm 2 2.90 4.20 4.76
n2 x 10-16
cm 2/W3.74 3.10 1.17
σ/n2
(W)0.78 1.35 4.07
The measured value of n2 is smaller than that of phosphate glass (LHG-8)and silicate glass (Q-88). This may be because glasses with compositionshaving low atomic number cations and anions have small opticalpolarizability leading to low refractive index and hence smaller n2 values.
The most interesting out come from the value of σ/n2 is that it is quite large(3 to 4 times) than those found in commercial glasses
26
All the laser spectra show similar features: The emission spectra are centered around 1047 nm. The spectral widths show nosignificant changes as a function of pump power exception made of the expected
broadening.
Wavelength (nm)0 20 40 60 80 100 120 140 160
0
5
10
15
20
25
30
Lase
r ou
t put
(m
j/pul
se)
Optical input (mj/pulse)
Nd: Glass out put (Commercial)Nd: BeL out put Nd: YAG out put Our Nd:Ph glass
Slope efficiency is around 20%
LASER ACTION RESULTS
Room temperature steady-state emission spectra of the4F3/2 →
4I9/2,11/2 transitions for different Nd 2O3 concentrations
The shape of the emission for the laser transition does not changesignificantly when increasing concentration. The 4F3/2→
4I9/2 emissionshows a different spectral profile as concentration increases due toreabsorption and the emission is inhomogeneously broadened due to site-to-site variations in the local ligand field.
Optics Express, vol. 19 (2011) 19444
860 nm1054
850
1330
(a) Excitation spectra of the 4I9/2→4F3/2 transition obtained by monitoring
at different emission wavelengths along the 4F3/2 →4I11/2 transition
for the sample doped with 0.5 mol% of Nd 2O3.(b) Emission spectra in the excitation range of 871-881 nm .
The emission peak shows a tunability of around 15 nm .Optics Express, vol. 19 (2011) 19444
a b
Dy3+-doped transparent oxyfluoride glassesand nanocrystalline glass -ceramics
Composition (in mol %)30SiO2–15Al 2O3–29CdF2–22PbF2–(4–x)YF3–xDyF3, where x = 0.01, 0.1 and 1.0 mol %
XRD Pattern
Partial energy level diagram of Dy 3+ ions
Visible and NIR emission spectra and CIE 1931 Chrom aticity diagram for Dy 3+-doped glass and glass-ceramics
Chromaticity color coordinates ofvisible emissions have beencalculated and are found to be in thewhite light zone.
IR emission spectra of the glassand GCs contain the 1.33 and1.67 µm emission bands usefulfor optical amplification intelecommunications.
31
Ultra-short laser pulses focused inside a transparent material can create localizedstructural changes.
When the laser intensity in the focal volume is high enough multiphoton absorption,avalanche ionization, optical breakdown and microplasma formation take place,leading to refractive index change at the focal region.
Since the absorption region is buried within the substrate matrix, the ablation ofmaterial is not possible. However, the heated material is expanding, creating astrain distribution around it.
The exact dynamics of the expansion is determined by the laser characteristics(intensity, pulse duration, focusing conditions, repetition rate, etc.) and theproperties of the matrix itself.
The strain left in the material can result in a very complex distribution of therefractive index around the irradiated region.
When a continuous line is written with appropriate laser parameters, a refractive-index profile inside the transparent material can be generated that acts as awaveguide.
FABRICATION OF WAVEGUIDES
32
corecladdingNo light lost-claddingallows complete internal reflection
LightWithout cladding, lightgradually leaks
out
Incidence
Optical fibers
Writing set up for optical waveguide devices
Ultrashort laser pulses are tightly focussedinto the bulk material
At the focus, the material is modified
3-dimensional structures can be directlyinscribed by translating the samplethrough the focus in three dimensions
(a) Optical microscope facet image of the optimal waveguide in SBZEu10 glass
(b) 635 nm near-field mode image of the fabricated waveguide
(c) Image of the standard end facet of the corning SM 600
(b)
MFD for waveguide : ∼ 5.74 µmMFD for SM600 : 4.3 µm
(a)
(c)
33
Eu3+- DOPED FLUOROSILICATE GLASS- WAVEGUIDE CHARACTERIZATION
Fig. Confocal micro fluorescence spectrum (a), spatial map ofthe peak intensity (b), frequency shift (c) and inducedbroadening (d) of the 615 nm fluorescence line of Eu3+ ionsin SBZEu10 glass with respect to the bulk over the laser-modified region.
MICRO FLUORESCENCE MEASUREMENTS
2 mm/s 1 mm/s 0.5 mm/s 0.25 mm/s
Waveguide image
(283mW and 0.25 mm/s)
(b)
Insertion loss (I.L) : 2.82 dB, Propagation loss (P.L): 1.81 dB/cm Best among all the Waveguides
Fiber image (SM600)
(a)
(c)
Waveguides fabricated with Yb3+-doped cavity dumped laser at 1047 nm wavelength with 1.0 MHz repetition rate produces 360 fs pulses
(a) Channel waveguides fabricated at 283 mW power with different scan speeds
(b) Best waveguide fabricated at 283 mW power with 0.25 mm/s scan speed
(c) Comparison of MFD for the waveguide fabricated and Standard SM600 fiber
CHANNEL WAVEGUIDES INSCRIBED IN Tb3+:SiNbKZn GLASS
Micro-Raman spectra of exposed tracks asa function of exposure energy. Traces aredisplaced vertically for comparison. Thehighest trace is for unmodified point (bulk);traces for exposures of 330, 314, 289 and269 nJ are also shown. The writing speedwas 0.25 mm/s.
Unpolarized micro-Raman spectrarecorded at A (modified) and B(unmodified) positions (shown in theinset) for the optimal waveguide withpulse energy of 283 nJ and scan speedof 0.25 mm/s written in Tb3+:SiNbKZnglass.
500 1000 1500 2000 2500 3000
Ram
an in
tesn
ity
(a. u
.)
Raman shift (cm-1)
Un-exposed Exposed
500 1000 1500 2000 2500 3000 3500 4000
(e)(d)(c)
(b)
Ram
an in
tens
ity
(a. u
.)Raman shift (cm-1)
(a)
(a) Bulk(b) 330 nJ(c) 314 nJ(d) 289 nJ(e) 269 nJ
Fig. 3D rending of the monolithic opticalstretcher fabricated by femtosecond lasermicromaching. The cells flowing in themicrochannel are trapped and stretched incorrespondence of the dual beam trap created bythe optical waveguides.
APPLICATIONS FS LASER IRRADIATION
optical waveguides,
photonic crystals
amplifiers inside
glasses
Raman waveguide
amplifiers
silicon semiconductors
etc.
Bellini et.al, Optics Express, Vol. 18, Issue 5, pp. 4679-4688 (2010)
Hydrostatic chamber
500 microns
180 microns
HPDO – “Four Posts”
HIGH PRESSURE TECHNIQUE – DIAMOND ANVIL CELL
Hydrostatic chamber
500 microns
180 microns
Hydrostatic chamber
500 microns
180 microns
Hydrostatic chamber
Hydrostatic chamber
1 GPa = 104 atm
Pressure calibrant : Ruby
Pressure determination from shift of ruby R1, R2fluorescence lines:
dνdp = -7.53 cm-1/GPa
14300 14350 14400 14450
11.9 GPa
5.0 GPa
0.0 GPa
Inte
nsity
(ar
b. u
nits
)
Wavenumber (cm-1)
R1 R2
Pressure transmitting medium:Methanol : ethanol : water (16:3:1 )
HIGH PRESSURE TECHNIQUE – DIAMOND ANVIL CELL
Pressure determination from shift of ruby R1, R2fluorescence lines:
dνdp = -7.53 cm-1/GPa
Pressure determination from shift of ruby R1, R2fluorescence lines:
dνdp = -7.53 cm-1/GPa
Pressure determination from shift of ruby R1, R2fluorescence lines:
dνdp = -7.53 cm-1/GPa
EMISSION SPECTRA OF Sm 3+:PPNSm05 GLASS UNDER PRESSURE
The spectral peaks are assigned to 4G5/2 →6HJ (J = 9/2, 7/2, 5/2) transitions
which correspond to the wavelengths of 644, 597 and 561 nm .
Peak positions - the lower region (red shift) and 4G5/2 →6H5/2, 7/2 multiplets
show the partially lifted degeneracy under increasing pres sure.
Energy Positions
Term Energy shift, (ααααi) (cm-1/GPa)
Increasingpressure
Decreasingpressure
6H5/2 -5.3 3.96H7/2 -4.9 3.86H9/2 -4.3 2.8
Ei (p) = E i (0) + αip
For instance, the shift of themanifolds with respect to eachother is due to variations inelectrostatic interactions, variationof the spin-orbit couplingparameter ( ξ4f) and strength andsymmetry of the crystal-field (CF)about the Sm 3+ ions.
Decay curves of Sm 3+-doped PPNSm05 glass
Non-exponential nature in the entire pressure range studie d.
The decay curves are well fitted to YT model for S = 6 indicatin gthat the energy transfer process is of dipole-dipole type an dmigration also plays an important role.
The lifetime and Q follow the opposite trend with increasing pressure.
The decrease of lifetimes could be explained by the variatio ns in theelectronic transition probabilities.
The lifetime ττττ and relative donor quantum yield decrease by about afactor of 3.5 from ambient condition to 23.6 GPa for PPNSm 05 glass.
44
Lanthanide-doped phosphate, silicate, tellurite and oxyfluoride glasses and glass-ceramicshave been prepared and physical, optical, laser and decay properties were characterizedsystematically and quantitative optical properties have been estimated which are prerequisitefor the design of any optical devices.
Laser action is found in our glasses and efforts are being made to scaling the dimension ofglasses besides to improve the efficiency beyond 22 %.
The glasses and GCs have potential applications such as visible and IR laser, color displaydevices, optical amplifier, etc.
Luminescence properties under pressure strengthens to understand Ln-Ligand-radiationinteraction mechanism as well as can be explored for pressure sensor applications.
Systematic study of the inscription of active waveguides in Tb3+-doped glass andcharacterization of microstructural changes induced at the focal volume by ultrafast laserpulses associated with the bulk properties have been carried out.
Looking forward for your comments/collaboration tostrengthen our research activities for the developmentPHOTONIC DEVICES based on Ln3+:glasses and glass-ceramics.
CONCLUSIONS
FUTURE WORK To carry out laser experiments with Nd 3+, Ho3+, Er3+,Tm3+ and Yb 3+-doped
glasses and glass-ceramics as gain media for the developmen t of efficientlasers.
To optimize the optical properties of Ln 3+-doped glasses at varioustemperatures .
To select, prepare and optimize various optical materials d oped withdifferent Ln 3+ ions to realize efficient solid state lightening and displa yapplications.
To extend the high pressure studies on various Ln 3+ ions to acquireknowledge about the luminescent properties in a single host by acontinuous change in Ln 3+-ligand bonding for sensor applications.
To progress the Ln 3+-doped glasses as an optical gain media whereoptimization of composition and dopant concentration is re quired to writewaveguides for photonic applications.
46
www.tirumala.org
www.svuniversity.inEstablished in 195458 Dept.71 PG courses450 Faculty1400 Non-teaching6000 students
47
THANK YOU