Third order nonlinear optical properties of bismuth zinc borate glassesB. Shanmugavelu, V. V. Ravi Kanth Kumar, R. Kuladeep, and D. Narayana Rao

Citation: Journal of Applied Physics 114, 243103 (2013); doi: 10.1063/1.4858422 View online: http://dx.doi.org/10.1063/1.4858422 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/114/24?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Optical properties of Dy3+ doped bismuth zinc borate glass and glass ceramics AIP Conf. Proc. 1447, 579 (2012); 10.1063/1.4710136 Optical Properties of Alkaline Earth Ions Doped Bismuth Borate Glasses AIP Conf. Proc. 1349, 545 (2011); 10.1063/1.3605974 Effect of SnO addition on optical absorption of bismuth borate glass and photocatalytic property of thecrystallized glass Appl. Phys. Lett. 92, 141902 (2008); 10.1063/1.2903151 Third-order nonlinear optical properties of bismuth-borate glasses measured by conventional and thermallymanaged eclipse Z scan J. Appl. Phys. 101, 033115 (2007); 10.1063/1.2434940 Third-order nonlinear optical properties of chalcogenide glasses Appl. Phys. Lett. 70, 925 (1997); 10.1063/1.118443

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54

Third order nonlinear optical properties of bismuth zinc borate glasses

B. Shanmugavelu,1 V. V. Ravi Kanth Kumar,1,a) R. Kuladeep,2 and D. Narayana Rao2

1Department of Physics, Pondicherry University, Puducherry 605 014, India2School of Physics, University of Hyderabad, Hyderabad 500046, Andhra Pradesh, India

(Received 8 October 2013; accepted 10 December 2013; published online 30 December 2013)

Third order nonlinear optical characterization of bismuth zinc borate glasses are reported here

using different laser pulse durations. Bismuth zinc borate glasses with compositions

xBi2O3-30ZnO-(70-x) B2O3 (where x¼ 30, 35, 40, and 45 mol. %) have been prepared by melt

quenching method. These glasses were characterized by Raman, UV-Vis absorption, and Z scan

measurements. Raman and UV-Vis spectroscopic results indicate that non-bridging oxygens

increase with increase of bismuth content in the glass. Nonlinear absorption and refraction

behavior in the nanosecond (ns), picosecond (ps), and femtosecond (fs) time domains were studied

in detail. Strong reverse saturable absorption due to dominant two-photon absorption (TPA) was

observed with both ps and fs excitations. In the case of ns pulse excitations, TPA and free-carrier

absorption processes contribute for the nonlinear absorption. Two-photon absorption coefficient (b)

and the absorption cross section due to free carriers (re) are estimated by theoretical fit of the open

aperture Z-scan measurements and found to be dependent on the amount of bismuth oxide in the

glass composition. In both ns and fs regimes the sign and magnitude of the third order nonlinearity

are evaluated, and the optical limiting characteristics are also reported. VC 2013 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4858422]

I. INTRODUCTION

Materials that possess good nonlinear optical (NLO)

properties have received much attention because of their

potential applications in various photonic devices.1 A wide

range of materials such as crystals, nanomaterials, quantum

dots, thin films, glasses, glass ceramics, and polymers have

been investigated for their nonlinear optical properties.2–13

Among several interesting candidates for photonic applica-

tions, glasses are receiving special attention because of their

good chemical and mechanical stability and their ease in fabri-

cating waveguides and fibers. Owing to the excellent adjust-

ability of compositions, glasses can be prepared and explored

to tune the desired property for a specific application. Glasses

having large nonlinear refractive index, fast response time,

and nonlinear absorption coefficient are promising materials

for nonlinear optical devices such as ultrafast optical switches

and optical power limiters. Therefore much effort is also gone

in the development of heavy metal oxide based glasses for

photonic applications.14–16 The presence of heavy-metal

oxides such as Bi2O3, PbO, and WO3 in the glasses increase

the nonlinear refractive index of a medium. The nonlinear op-

tical properties can be tailored by choosing the appropriate

oxides with large hyperpolarizabilities and large transmit-

tance. In particular glasses containing bismuth oxide attracts

much attention because of their high refractive indices and

large transmission window in the visible and near infrared.

They are also very stable and moisture resistant. The presence

of bismuth oxide in borate, phosphate, germinates, and tellur-

ite glasses has been investigated.17–20 Among the various

glass systems borate glasses are frequently used as good host

matrices for incorporating heavy metal oxides. Recently,

Gomes et al. studied the influence of bismuth oxide in borate

glasses on third order nonlinear optical properties by conven-

tional and thermally managed eclipse Z-scan methods and op-

tical limiting measurements.21,22 They found enhancement of

two-photon absorption cross section and free carrier absorp-

tion cross section with the increase of bismuth oxide content

in the zinc borate glass. The nonlinear optical properties of the

glasses can be enhanced by increasing the amount of bismuth

oxide concentration in the sample. This drives us to optimize

the bismuth oxide content in the glass and develop new

glasses with high optical nonlinearity. Keeping this in view,

zinc borate glasses are prepared for various bismuth oxide

concentrations and reported the thermal and electrical proper-

ties recently.23,24 In the present work, the nonlinear optical

properties of glasses as a function of bismuth oxide concentra-

tion have been investigated.

II. EXPERIMENTAL DETAILS

The glasses with compositions of xBi2O3-30ZnO-(70-x)

B2O3 (where x¼ 30, 35, 40, and 45 mol. %), hereafter

denoted as BZB30, BZB35, BZB40, and BZB45 were pre-

pared by melt quenching technique using analar grade chem-

icals Bi2O3, ZnO, and H3BO3. Each batch of the chemicals

in an appropriate composition were mixed and melted in a

platinum crucible in the temperature range 900–1000 �C for

1 h. The melt was swirled frequently to ensure homogeneity.

The melt was then quickly quenched by pouring and pressing

between two stainless steel plates. The prepared glasses were

annealed to remove the thermal stress. The glasses were then

ground and finally polished to a thickness of 1 mm to make

them suitable for optical measurements. The Raman spectra

have been recorded in the range of 50–2000 cm�1 using

a)Author to whom correspondence should be addressed. Electronic mail:

ravi.phy@pondiuni.edu.in. Tel.: þ91 413 2654406. Fax: þ91 413 2655368.

0021-8979/2013/114(24)/243103/6/$30.00 VC 2013 AIP Publishing LLC114, 243103-1

JOURNAL OF APPLIED PHYSICS 114, 243103 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54

Renishaw inVia Raman microscope with 488 nm argon ion

laser. UV-visible absorption spectra were recorded using

Carry 5000 UV-Vis-NIR spectrophotometer. The nonlinear

absorption and refraction properties of the glasses are studied

using 800 nm femtosecond (fs), 532 nm picosecond (ps), and

nanosecond (ns) pulses through the standard single beam

Z-scan technique.25 The ns laser source was a frequency

doubled Nd:YAG laser (INDI-40, Spectra-Physics) with a

6 ns pulse duration and a repetition rate of 10 Hz at a 532 nm

wavelength, ps laser source was a frequency doubled,

Q-switched Nd:YAG (EKSPLA-2143a) delivering 30 ps

laser pulses at 532 nm at a repetition rate of 10 Hz and fs

laser was a Spectra-Physics Ti-sapphire regenerative ampli-

fier with �110 fs pulse duration, operated at 1 kHz repetition

rate and 800 nm wavelength. Z-scan studies were carried out

by focusing the input beam on to the sample using a lens of

120 mm focal length forming 27 lm and 40 lm spot sizes at

the focus with 532 nm and 800 nm, respectively. Similar

peak intensities were maintained in the scans to ensure iden-

tical experimental conditions for all the glass samples.

Closed aperture scans were performed at lower intensities to

avoid contribution from the higher order nonlinear effects.

The experiments were repeated more than once and the best

data were used for obtaining the nonlinear optical coeffi-

cients from the best fits.

III. RESULTS AND DISCUSSION

A. Absorption and Raman studies

The linear optical absorption spectra of the glasses are

shown in Fig. 1. The absorption edge of these glasses shifts

to longer wavelengths with increase of Bi2O3 content. The

optical band gap value of the samples were determined from

Tauc plots,26 shown in Fig. 2, and found to be 2.71 eV

(BZB30), 2.59 eV (BZB35), 2.47 eV (BZB40), and 2.13 eV

(BZB45). The optical bandgap decreases with increase of

Bi2O3 content. This indicates that increase of bismuth oxide

content increases the non-bridging oxygens (NBOs) in the

glass matrix. NBOs are oxygen atoms bonded to only one

network cation and negatively charged, which is important

for nonlinear optical materials.11

The Raman spectra of the glasses are shown in Fig. 3.

The spectra exhibit bands at 73, 136, 360, 600, 935, and

1300 cm�1. The low frequency band observed at 73 cm�1 is

the characteristic boson peak of glasses.27 The band located

at 136 cm�1 is assigned to the heavy metal ion vibrations.28

The band at 360 cm�1 is attributed to bridging anion modes

of Bi–O–Bi vibrations in the distorted BiO6 octahedra.28 The

band located at around 600 cm�1 is assigned to the Bi–O�

stretching vibration (i.e., vibration of bismuth associated

with non-bridging oxygen) of the BiO6 octahedral units.28

The band centered around 935 cm�1 is ascribed to the ortho-

borate groups.29 The band at 1300 cm�1 is due to the stretch-

ing of the terminal B–O� bonds of the pyroborate groups.29

The intensity of the band centered at around 600 cm�1

increase with the increase of Bi2O3 content, which indicates

that BiO6 groups containing NBOs increases. The band pres-

ent at 1300 cm�1 shifts to lower wavenumber side with

FIG. 1. UV-Vis absorption spectra of BZB glasses with different Bi2O3

concentrations.

FIG. 2. Tauc’s plots of BZB glasses with different Bi2O3 concentrations.

FIG. 3. Raman spectra of BZB glasses with different Bi2O3 concentrations.

243103-2 Shanmugavelu et al. J. Appl. Phys. 114, 243103 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54

decrease in intensity as the Bi2O3 content increases showing

the enhancement of asymmetric vibration.30

B. Z scan measurements

The nonlinear absorption and refraction measurements

were carried out using Ti:sapphire femtosecond laser. Figure 4

shows representative open aperture Z-scan curves of the glasses

with different Bi2O3 concentration recorded with 800 nm using

�110 fs pulses at a peak irradiance of 220 GW cm�2. A strong

reverse saturable absorption (RSA) kind of behavior is

observed for all the glass samples. The magnitude of the non-

linear absorption coefficient was determined for each sample

by analyzing the light attenuation through the sample given by

dIðzÞdz¼ �a0IðzÞ � bI2ðzÞ � cI3ðzÞ; (1)

where

Iðz; tÞ ¼ I00

x20

x2 zð Þ

!:exp

�2r2

x2 zð Þ

!:exp

�t2

s2p

!;

xðzÞ ¼ x0 1þ�

z

z0

�2" #1

2

;

z0 ¼px2

0

k:

a0 is the linear absorption coefficient, b is the two photon

absorption coefficient (TPA), c is the three photon absorption

coefficient (3PA), z0 is the Rayleigh range, x0 is the beam

waist at focus, I is the intensity as a function of r, t, and z, I00

is peak intensity at the focus of the Gaussian beam, and sp is

the input pulse width used. The differential equations are

solved numerically using Runge-Kutta fourth order method.

The differential equations are first de-coupled and then inte-

grated over time, length, and along the radial direction.

Assuming the input beam to be a Gaussian, the limits of inte-

gration for r, t, and z are varied from 0 to1, �1 to1, and

0 to L (length of the sample), respectively. Typical number

of slices used for r, t, and z are 30, 20, and 5, respectively.

The two-photon absorption coefficient b and three-photon

absorption coefficient c are then estimated through least

square fit of the experimental data. The Z-scan curves

recorded at 60 and 220 GW/cm�2 are found to be best fitted

with TPA alone and the 3PA (c) contribution is negligible.

However it is observed that c makes a small contribution at

higher intensities. The estimated value of c at 705 GW/cm�2

is found to be 0.42� 10�24 cm3 W�2 which is very low.

Observed open aperture Z-scan experimental data were

fitted with the Eq. (1) and obtained best fit parameters are

listed in Table I. Solid lines in figure represent theoretical fit

obtained by using Eq. (1). Estimated two photon absorption

coefficient values of the glasses for various Bi2O3 concentra-

tions are given in Table I. The two photon absorption coeffi-

cient increases with increase of Bi2O3 content; this can be

attributed to the increase in the NBOs content. Since NBOs

are less stable and weakly bound to the boron or bismuth

atoms, its valence electrons are easily deformable by the

laser electromagnetic field, resulting in larger nonlinear-

ities.11 The Raman and absorption studies also indicate that

NBOs increase with increase of bismuth oxide concentration

in the glasses. Figure 5 illustrates the typical closed aperture

Z-scan curve obtained for BZB45 glass sample with a peak

intensity of 9.4 GW cm2. Closed aperture Z-scan experiments

on the glass samples confirm that they exhibit positive nonli-

nearity. It may be noted that the experiments were carried

out with 1 KHz rep rate and if thermal nonlinearity was to

play a role, then negative nonlinearity might have been

observed. To eliminate the contribution of nonlinear

absorption the closed aperture data was obtained at a lower

FIG. 4. Open aperture Z-scan curves of the BZB glass samples of different

Bi2O3 concentrations with 800 nm, 110 fs pulses. Solid curves are the theo-

retical fit to the experimental data.

TABLE I. Measured values of two photon absorption coefficients (b), free carrier absorption cross section (re), and optical limiting threshold values of bis-

muth zinc borate glasses under fs, ps, and ns regimes.

k ¼ 800 nm, sp¼ 110 fs k¼ 532 nm, sp¼ 30 ps k¼ 532 nm, sp¼ 6 ns

Sample b (cm/GW) Optical limiting threshold (GW/cm2) b (cm/GW) re (�10�19 cm2) Optical limiting threshold (GW/cm2)

BZB30 0.18 61.2 7.2 58.0 0.347

BZB35 0.47 49.6 12.5 83.0 0.304

BZB40 0.78 37.4 17.8 126.0 0.225

BZB45 1.04 27.8 24.6 157.0 0.190

BZH221,22 <0.01 … 5.5 6 0.2 6.7 …

243103-3 Shanmugavelu et al. J. Appl. Phys. 114, 243103 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54

intensities and the data has been divided with the open aper-

ture data. The normalized curve is shown in Fig. 5.

The closed aperture data were fitted with the Eqs. (2)

and (3) (Ref. 25)

TCA ¼ 1� 4D/0ðz=z0Þ½1þ ðz=z0Þ2�½9þ ðz=z0Þ2�

; (2)

where D/0 is the phase change of the laser beam due to non-

linear refraction. D/0 value is estimated by fitting the experi-

mental data

n2ðcm2W�1Þ ¼ jD/0jk2pI00Lef f

: (3)

The magnitude of the nonlinear refractive index n2 evaluated

is found to be þ0.98 � 10�15 cm2 W�1 and þ1.5 � 10�15

cm2 W�1 for BZB30 and BZB45 glass samples, respectively.

It indicates that the nonlinear refractive index increases with

increase of bismuth oxide content in the glass.

Z scan measurements were also performed at 532 nm in

both ps and ns regimes. Figure 6 shows the respective open

aperture scan data of glasses with different Bi2O3 concentra-

tion obtained with 532 nm, 30 ps pulses. The reverse satura-

ble absorption is observed for all the glass samples at

4.28 GW cm�2. For the ps and ns data, the contribution due

to 3PA (c) is neglected. Observed open aperture Z-scan ex-

perimental data were fitted with the Eq. (1) (solid line in Fig.

6), and obtained best fit parameters are listed in Table I. In

this case also estimated two photon absorption coefficient

values of the glasses were found to be dependent on the

amount of bismuth oxide in the glass composition and attrib-

uted to more NBOs.

Z-scan measurements were also performed at 532 nm, 6 ns

pulses. Figure 7 shows representative open aperture Z-scan

curves of the glasses with different Bi2O3 concentration

recorded with 532 nm, 6 ns pulses at a peak irradiance of

1.18 GW cm�2. The open aperture Z-scan studies revealed

RSA behavior of the glasses with different Bi2O3 concentration.

The free carrier absorption (FCA) cross section was determined

for each sample by analyzing the light attenuation through the

samples, that is described by

dIðzÞdz¼ �a0IðzÞ � bI2ðzÞ � reNIðzÞ; (4)

where re is the free carrier absorption cross section and N

being the photogenerated free-carrier density governed by

the equation

dN

dt¼ a0IðzÞ

�hxþ bI2ðzÞ

2�hx: (5)

For a Gaussian laser pulse represented by Iðz; tÞ ¼ IðzÞexpð�t2=s2

pÞ, where sp is the laser duration, one obtains

N ¼ ½ða0spffiffiffipp

=�hxÞIðzÞ� þ ½ffiffiffiffiffiffiffiffip=2

pðbsp=2�hxÞI2ðzÞ�. After

substituting in Eq. (4), this leads to

FIG. 5. Closed aperture Z-scan curve of the BZB45 glass sample at 800 nm,

110 fs pulses. Solid line is the theoretical fit with Eq. (2).

FIG. 6. Open aperture Z-scan curves of the BZB glass samples of different

Bi2O3 concentrations with 532 nm, 30 ps pulses. Solid curves are the theo-

retical fit to the experimental data.

FIG. 7. Open aperture Z-scan curves of the BZB glass samples of different

Bi2O3 concentrations with 532 nm, 6 ns pulses. Solid curves are the theoreti-

cal fit to the experimental data.

243103-4 Shanmugavelu et al. J. Appl. Phys. 114, 243103 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54

dIðzÞdz¼ �½a0 þ bþ ðrea0sp

ffiffiffipp

=�hx� �

IðzÞ

þ ðrespbffiffiffiffiffiffiffiffip=2

p=2�hxÞI2ðzÞ�IðzÞ: (6)

The above differential equation is solved numerically using

Runge-Kutta fourth order method. Equation (6) has two pa-

rameters b and re, the values of b at 532 nm, which were

measured in the picosecond regime, were used to estimate re

through least square fit of the experimental data. Solid lines

in Figure represent a theoretical fit using Eq. (6).

The data obtained with ns pulses was fitted using Eq. (6),

and the obtained best fit parameters are listed in Table I. From

Table I one can see that the free carrier absorption cross sec-

tion increases with increase of bismuth oxide content in the

glass. The observed values of two photon absorption coeffi-

cient and free carrier absorption cross section for 532 nm

wavelength in the present work are found to be higher than

that of the previous results obtained by Gomes et al. for bis-

muth zinc borate glass with 25 mol. % of bismuth oxide.21,22

This increase is due to the presence of higher amount of bis-

muth content in the present studied glasses. Figure 8 shows

the typical closed aperture Z-scan curve obtained for BZB45

glass sample with a peak intensity of 87 MW cm�2, nearly

symmetric profile of peak followed by a valley, indicative of

negative nonlinearity. Observation of negative nonlinearity on

excitation with ns pulses is common and is attributed to the

thermal effects in the glass generated by high fluence of ns

laser pulses. The closed aperture data was fitted with the Eq.

(2). The magnitude of the nonlinear refractive index n2 eval-

uated is found to be�6.9 � 10�12 cm2 W�1. Since the magni-

tude of the electronic nonlinearity as measured through fs

laser experiment is nearly three orders of magnitude weaker,

the measured nonlinearity in the case of ns pulses can be

mainly attributed to the thermal nonlinearity.

From the application point view, the glasses having high

nonlinear index and small two photon absorption coefficient

can be considered as a good candidate for ultra fast optical

switch in an optical fiber communications system. The

suitability of the optical switching characteristics of the

materials can be determined by its figures of merit

F ¼ 2bkn2

: (7)

The value of F must be less than 1 for a good optical switch.

The value of F for the BZB45 glass is greater than 1 at 800

and 532 nm. This is due to the presence of high two photon

absorption, which affects the optical switching performance

of the glass. Since the present glasses exhibited relatively

strong two photon absorption, they are unsuitable for optical

switching but can be used in the devices like optical limiters.

C. Optical limiting

One of the applications of reverse saturable absorbing

materials in devices is based on optical limiters. Optical lim-

iters are the materials that allow light to pass through them at

low input intensities, but limit the transmittance to a thresh-

old value at higher intensities. Optical limiters are used to

protect human eyes or optical sensors from high fluence irra-

diation. In order to check whether Bismuth Zinc Borate

FIG. 8. Closed aperture Z-scan curve of the BZB45 glass sample at 532 nm,

6 ns pulses. Solid line is the theoretical fit with Eq. (2).

FIG. 9. Optical limiting response of BZB glass samples (a) at 800 nm wave-

length with pulse duration of 110 fs pulses and (b) at 532 nm wavelength

with pulse duration of 6 ns.

243103-5 Shanmugavelu et al. J. Appl. Phys. 114, 243103 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54

glasses behave as optical limiters, the nonlinear transmission

of the glasses were studied as a function of the input fluence.

The optical limiting curves of the glass samples in both fs

and ns regimes are shown in Fig. 9. Bismuth zinc borate

glasses showing good limiting threshold behavior in both ns

and fs pulse regimes and at two different wavelengths sug-

gests that these glasses can act as a broad band optical

limiter.

In summary, Z-scan studies were carried out to find the

third order nonlinearities of bismuth zinc borate glasses. At

800 nm in the fs regime, TPA is dominant mechanism at

lower intensities, whereas at higher intensities a small contri-

bution of three photon absorption is found. Both the TPA

coefficient b and nonlinear refractive index n2 values are

found to increase with the increase in Bi2O3 amount in glass

composition. With 532 nm excitation, TPA still dominates in

the ps regime while TPA and free carrier absorption are

found to be responsible for light attenuation in the ns pulse

regime. Under 532 nm excitation also it was found that TPA

coefficient b (in ps regime) and free carrier absorption coeffi-

cient re values increase with increase of bismuth oxide con-

tent in the glass composition. The enhancement in the

nonlinear optical parameters at 800 nm (fs), 532 nm (ps and

ns) with the increase of Bi2O3 concentration in bismuth zinc

borate glasses of present studies can be attributed to the

increase of the NBOs in glasses.

IV. CONCLUSIONS

Raman and linear absorption spectra results indicate that

NBOs increases with increase of bismuth oxide in the

glasses. From Z scan measurements, electronic and thermal

nonlinearity contributions through fs and ns excitations are

obtained. Experiments with fs pulse duration reveals that the

material show positive nonlinearity while the sign is negative

in ns regime. With both the ps and fs excitations the two pho-

ton absorption coefficient was found to increase with

increase of Bi2O3 content and this can be attributed to the

increase in the NBOs content. In the ns regime, the free car-

rier absorption cross section increases with increase of bis-

muth oxide content in the glass. The present studied bismuth

zinc borate glasses also exhibit good optical limiting

properties.

ACKNOWLEDGMENTS

The authors thank Central Instrumentation Facility,

Pondicherry University (India) for providing UV-Vis and

Raman characterization facilities. NLO characterization of the

glass samples was done at University of Hyderabad (India).

R. Kuladeep acknowledges University Grants Commission

(UGC), India, for providing fellowship. This work was

supported by University Grants Commission, New Delhi, India

under Major research project (No. 39-472/2010).

1R. L. Sutherland, in Handbook of Nonlinear Optics, 2nd ed., edited by

D. G. McLean and S. Kirkpatrick (Dekker, New York, 2003).2J. N. B. Reddy, V. B. Naik, S. Elizabeth, H. L. Bhat, N. Venkatram, and

D. N. Rao, J. Appl. Phys. 104, 053108 (2008).3L. Polavarapu, N. Venkatram, W. Ji, and Q.-H. Xu, ACS Appl. Mater.

Interfaces 1, 2298 (2009).4J. Olesiak-Banska, M. Gordel, R. Kolkowski, K. Matczyszyn, and M.

Samoc, J. Phys. Chem. C 116, 13731 (2012).5C. S. Yelleswarapu, G. Gu, E. Abdullayev, Y. Lvov, and D. V. G. L. N.

Rao, Opt. Commun. 283, 438 (2010).6N. Venkatram, R. S. S. Kumar, and D. N. Rao, J. Appl. Phys. 100, 074309

(2006).7N. Venkatram, D. N. Rao, and M. A. Akundi, Opt. Express 13, 867

(2005).8S. Mathew, A. D. Saran, B. S. Bhardwaj, S. A. Joseph, P. Radhakrishnan,

V. P. N. Nampoori, C. P. G. Vallabhan, and J. R. Bellare, J. Appl. Phys.

111, 074312 (2012).9A. Chen, G. Yang, H. Long, P. Lu, W. Zhang, and H. Wang, Mater. Lett.

91, 319 (2013).10S. Porel, N. Venkatram, D. N. Rao, and T. P. Radhakrishnan, J. Appl.

Phys. 102, 033107 (2007).11J. M. P. Almeida, L. De Boni, A. C. Hernandes, and C. R. Mendonca, Opt.

Express 19, 17220 (2011).12T. R. Oliveira, L. d. S. Menezes, C. B. de Ara�ujo, and A. A. Lipovskii,

Phys. Rev. B 76, 134207 (2007).13B. Karthikeyan, M. Anija, and R. Philip, Appl. Phys. Lett. 88, 053104

(2006).14T. Hasegawa, T. Nagashima, and N. Sugimoto, Opt. Commun. 250, 411

(2005).15E. L. Falc~ao-Filho, C. B. de Ara�ujo, C. A. C. Bosco, G. S. Maciel, L. H.

Acioli, M. Nalin, and Y. Messaddeq, J. Appl. Phys. 97, 013505 (2005).16G. Poirier, C. B. de Araujo, Y. Messaddeq, S. J. L. Ribeiro, and M.

Poulain, J. Appl. Phys. 91, 10221 (2002).17K. Imanishi, Y. Watanabe, T. Watanabe, and T. Tsuchiya, J. Non-Cryst.

Solids 259, 139 (1999).18D. Manzani, C. B. de Ara�ujo, G. Boudebs, Y. Messaddeq, and S. J. L.

Ribeiro, J. Phys. Chem. B 117, 408 (2013).19F. Chen, B. Song, C. Lin, S. Dai, J. Cheng, and J. Heo, Mater. Chem.

Phys. 135, 73 (2012).20T. Fujiwara, T. Hayakawa, M. Nogami, and P. Thomas, J. Am. Ceram.

Soc. 94, 1434 (2011).21A. S. L. Gomes, E. L. Falc~ao-Filho, C. B. de Araujo, D. Rativa, R. E. de

Araujo, K. Sakaguchi, F. P. Mezzapesa, I. C. S. Carvalho, and P. G.

Kazansky, J. Appl. Phys. 101, 033115 (2007).22T. R. Oliveira, L. de S. Menezes, E. L. Falc~ao-Filho, A. S. L. Gomes,

C. B. de Ara�ujo, K. Sakaguchi, F. P. Mezzapesa, I. C. S. Carvalho, and

P. G. Kazansky, Appl. Phys. Lett. 89, 211912 (2006).23B. Shanmugavelu and V. V. R. K. Kumar, J. Am. Ceram. Soc. 95, 2891

(2012).24B. Shanmugavelu and V. V. R. K. Kumar, Solid State Sci. 20, 59 (2013).25M. Sheik-Bahae, A. A. Said, T.-H. Wei, D. J. Hagan, and E. W. van

Stryland, IEEE J. Quantum Electron. 26, 760 (1990).26J. Tauc, R. Grigorovici, and A. Vancu, Phys. Status Solidi 15, 627 (1966).27E. Duval, A. Boukenter, and T. Achibat, J. Phys.: Condens. Matter 2,

10227 (1990).28A. A. Kharlamov, R. M. Almeida, and J. Heo, J. Non-Cryst. Solids 202,

233 (1996).29W. L. Konijnendijk and J. M. Stevels, J. Non-Cryst. Solids 18, 307 (1975).30G. Gao, L. Hu, H. Fan, G. Wang, K. Li, S. Feng, S. Fan, and H. Chen, Opt.

Mater. 32, 159 (2009).

243103-6 Shanmugavelu et al. J. Appl. Phys. 114, 243103 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

14.139.69.34 On: Wed, 11 Jun 2014 11:09:54