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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: ckjaya@yahoo.com

Indo-French Workshop on Glasses and Glass-ceramics, 6-8 June 2012, Lille, France

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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

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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.

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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

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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

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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

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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

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Partial energy level structure of Ln3+ ions

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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

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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

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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.

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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

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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

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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

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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)

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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

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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.

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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

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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)

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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.

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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.

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www.tirumala.org

www.svuniversity.inEstablished in 195458 Dept.71 PG courses450 Faculty1400 Non-teaching6000 students

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