Absorption and photoluminescence spectra of some rare earth doped B2O3TeO2BaOR2O (R = Li, Na, Li + Na) glasses

HI:

soo22-3@7(97)00210-2

J. Phys. C&m Solids VoI 59, No. 3, pp. 337-346, 1998 1997 Elsevier Science hd. All rights -ad Printed in Great Britain $19.00 + 0.00 0022-3697198

8

ABSORPTION AND PHOTOLUMINESCENCE SPECTRA OF SOME RARE EARTH DOPED 8203-Te02-BaO-R20 (R = Li, Na, Li + Na) GLASSES C. V. REDDY’**, Y. N. AHAMMEDb, R. R. REDDY b and T. V. R. RAOb aDepartment of Physics, S.K.U.P.G. Centre, Kumool5 18 001, India bDepartment of Physics, SK. University, Anantapur 5 15003, India (Received 13 May 1997; accepted 26 August 1997) Abstract---This paper reports the preparation and optical characterisation of certain rare earth (Sm’+, Dy3+. Eu3+) doped bcrotelhuite glasses of the following composition: B203 - TeOs - BaO - RsO - REF3 where R = Li, Na and Li + Na; RE = Sm3+.Dy3+ and &I’+ . From the measured spectra, absorption baud intensity parametrisation and luminescence characteristic parameters have been evaluated for tbe glasses investigated. Under a UV source, it was observed that Sm3+ doped glasses have beenluminescing in greenish-yellow, Dy’+ glasses in yellowish-blue and E~~~glasses in red coloun. These optical glasses are.found to be IR-transmitting (up to 4.5 pm) with good transparency and sufficient hardness. 0 1997 Elsevier Science Ltd. All rights reserved. Keywords: absorption spectroscopy,photoluminescence spectroscopy, rare earth metals, doping

Gli%SS

1. INTRODUCTION

type Over the past decade,

a great deal of work has been

carried out in the production

and detailed

analysis

of

kinds of glasses which were based on oxides, phosphates, borates, oxyphosphates, halides and oxyhalides [l-4]. Parallel to this work, some attention has been focused on the preparation and physical different

properties

of certain chalcogenide

and semiconducting

it has been stated that addition of TeOz into the glass matrices will enhance glass quality with an improvement in transparency, refractive index, density, durability towards moisture and enhancement in the IR transmission. In view of these improvements with the tellurite based glasses we have undertaken the present work, in order to understand both absorption and fluorescence spectral properties of borotellurite glasses containing three different rare earth ions (Sm3+, Dy’+, Eu3+) with content (R20) as the glass network modifier ions. glasses

[5-71. According to the literature,

2.1. Glass preparation

glasses

uv IR Transmission Transmission

350 nm Glass A 65BsOr + 2Te02 + lOBa -+-22Liz0 + tREF3 Glass B 65BsOr + 2Te02 + 360 nm lOBa + 22Na10 + 1REFl 360 nm Glass C 65BsOr -I- 2TeOr + lOBa + llLia0 + 1INas + 1REP+ (RE = Sm3+, Dy-+ and Et?+)

4.5 pm

4.3 pm

4.4 pm

These glasses were prepared by adopting the quenching technique [8]. Each of the above batch chemicals were melt at 950°C for half an hour in an electric furnace, The elements that were used were all spectrally pbre (H3B03, TeOz, BaC03, Li$Oj, NaC03, SmF3, DyF3 and EuF3). These glasses are found to be moisture resistant with an excellent transparency, possessing good IR transmission. The determination of refractive indices (fld) at 589.3 nm and densities of these glasses, was carried out and the results are given Mow: Glass type

2. EXPERIMENTAL

The following are the nine borotellurite prepared for their spectral analysis.

Composition (mol%)

Glass A Glass B Glass C

nd

d

(x589.3 nm)

(g cm-j)

1.5567 1.5485 1.5215

2.103 2.197 2.150

The above table clearly describes the dependence *Corresponding author.

refractive 337

of the

index and density values both on the changes

338

C.

V. REDDYet al.

Table 1.Electric dipole linestrengths (S,, X 10zo cm*), experimental oscillator strengths(fc,+x IO”), theoretical oscillator smqths (f,.~ X 106)and Judd-Ofelt intensity parameters(tl, X 102’cm*) for the Sm3+ doped glasses

Absorption

Glass A

Glass B f CLI

transition

s cd

fw

‘H 5i7-

0.6793 3.9600 3.0647

3.0923 3.0596 21.3062 21.5414 19.1543 19.2498 3333.260 18.199 171.293

4Gsn

- 4F,a - 4I,A/z 02 a4 n6

Sd

F w

0.6159 3.6388 2.7691

2.8033 19.4254 17.093 3022.438 16.443 157.434

made in the alkali content and also on the rare earth dopant ions present in the glass systems examined. 2.2. Spectral measurements

f cd

&i

fw

2.7585 19.6827 17.295

0.2806 3.6963 2.7793

1.2737 1.2602 19.8308 20.050 17.365 17.4083 1345.408 16.504 159.950

Absorption spectral profiles of the glasses are shown in Fig. l(a)-(c) for Sm3+, Fig. 2(a)-(c) for Dy3+ and Fig. 3(a)-(c) for Eu3+. From the spectra, the following are the absorption bands identified. Fig. l(a)-(c) (Sm’+ glasses)

Fig. 2(a)-(c) (Dy.‘+ glasses)

Fig. 3(a)-(c) (Eu3+ glasses)

6Hsn - 4GSn - 4Fjn - 41w2

6H IS/Z- +sn z p2

‘F,+ 5D, + 5D2 --t 5D3 + ?.,6

9f2

Absorption intensities have been evaluated for these measured bands. The intensity of a band is measured in terms of a quantity known as the oscillator strength (f). The experimental value of oscillator strength (f) is expressed in terms of molar extinction coefficient (e) and the energy of transition in wavenumber (v) by the following expression f =4.32 X 1O-9 E(Y)dv I

(2)

where c is the concentration of the system in mol l-‘, 1is the glass thickness and A is the absorptivity or optical density. In the present work c = 1 mol%, 1 = 0.3 cm and, hence, e = 3.33A 3.1. Spectral intensities

3. RESULTS AND DISCUSSION

4H~~n

f Cal

where dv is the band width at half height. The molar extinction coefficient (e) at a given energy (v) is computed from the Beer-Lambert Law. E= Alcl

Absorption spectra of these glasses were measured on a Perkin-Elmer 55 1 Spectrophotometer. Both excitation and emission spectra were carried out on a Hitachi F-3010 Spectrofluorimeter. We had access to this facility at Central Instrumentation Laboratory, University of Hyderabad, India.

-

Glass c

(1)

Theoretical estimates for the observed bands were made following the method of the Judd-Ofelt approach by considering only the electric dipole line strengths (S,&, as has been done by several other authors [9, lo]. 3.2. Judd-Ofelt method Judd [ 1l] and Ofelt [ 121 have independently derived expressions for the oscillator strengths of an induced electric dipole transition within the f * configuration. Since their results are similar and were published simultaneously, the basic theory has become known as the Judd-Ofelt theory. According to this theory

where Y(cm-‘) is the energy of the transition +J;I- $‘J’, lJx is a unit tensor operator of rank X, the sum running over three values X = 2, 4 and 6 and Th are three phenomenological parameters which are evaluated from the experimental data, and the values off,,rrffdc are given in Tables 1,2 and 3,

Table 2. Electric dipole linestrengths (&d X lo*’ cm*), experimental oscillator strengths (fcXpX 106),theoretical oscillator strengths (f,l X 10’) and Judd-Ofelt intensity parameters @‘I,+ X 10”’ cm ) for the Dy’+ doped gltises Absorption transition

9.1,sn

Q2

l-h 06

-

4F5n

-

+m 4F9/2 ‘+H15r2

Glass A

Glass B

SCd

f ew

f CA

&A

F w

11.9663 2.1145 2.1519 3.4485

14.228 1.8324 4.336 7.268 151.971 240.293 34.665

14.016 2.632 4.287 7.243

11.2615 1.990 6.0906 7.3701

12.334 4.597 11.738 15.344 672.506 1091.120 32.623

Glass C

f EBI

L

fw

f CA

13.117 2.463 12.065 15.393

8.1642 1.4427 1.7309 3.3604

9.704 0.926 3.398 7.023 1 239.414 219.844 23.651

9.536 1.790 3.438 7.038

Absorption and photoluminescence spectra of rare earth glasses (b)

.m 2

J

339

3.0

%2

2 8% 0.1

(c) too-

90

.

80'

70.

60. p

4s ‘%

3 E

50 .

$ .g

40.

E g

30.

I

8

45/

2

20.

10.

393

450

510

5

Fig. 1. (a)Absorption spectra of Sm”+ doped Glass A. (b) Absorption spectra of Sm-‘+ doped Glass B. (c)Absorption spectra of Sm’+ doped Glass C.

C. V. REDDY ef al.

340

(a)

(b)

3.0

35

6

I

!

I . LM

L80

540

1.

600

720

660

BO

uo

-b=d

wawte@h) (‘3

3.1 3-

2.L-

a ‘5

1.6.

% I

=r,

2 .r" E

.2 -

1' 8 ? tI.6.

360

&?I

160

640

600

660

720

mo

6&o

900

Fig. 2. (a) Absorption spectra of Dy.‘+ doped Glass A. (b) Absorption spectra of Dy’‘+ doped Glass B. (c) Absorption spectra of Dy ‘+ doped Glass C.

Optid

&cmity (orbitrary

units) z

units)

units)

Optical density (orbitnry

Opticu density brbitrilry

C. V. REDDYet al.

342

(fexP X 106), theoretical oscillator strengths Table 3. Electric dipole linestrengths (Sd X 10” cm2),experimental oscillator strenp (f,,, X 106) and Judd-Ofelt intensity parameters (& X IOU’cm ) for the Eu’+ doped glasses Absorption s ed

transition

‘F02 -

‘D,

-

‘D2 ‘D, 5L6

Glass B

Glass A

0.0633 0.0194 0.0745 0.5578

n2

04 a6

f ev

f CA

1.0818 3.3250 2.7544 21.7878 24.3585 54.0038 35.993 1

1.0818 0.6358 2.7544 21.7877

&d 0.0577 0.0177 0.0240 0.5629

In the intermediate coupling scheme, the states of the f N electronic configuration were taken as the linear combination

where C(crSL) are the numerical coefficients resulting from the simultaneous diagonalisation of the electrostatic and spin-orbit matrices. The matrix elements of eqn (3) were calculated on the LS basis using the equation (1IJllU”ll~‘J’) = (- l)s+L’+J+Q2J+

l)(U’ + l)]‘”

Glass C

F ev

f Cal

&d

f =P

f Cal

1.643 6.333 8.8432 21.6375 22.2160 193.1745 36.3183

1.617 0.572 8.6739 21.413

0.0315 0.0097 0.3406 0.5715

0.8931 4.6909 12.3307 21.8629 12.1338 279.7858 36.8754

0.8857 0.3137 12.3087 21.8028

3.3. Method of electric (SJ dipole linestrengths Theoretical spectral intensityfcan relation

be evaluated by the

where rtd is the refractive index of the medium, Sd the electric dipole linestrength, m the mass of an electron, c the velocity of light, h Plan&s constant, e the energy of an electron (in C), Ythe energy of the band (in cm-‘) and J is the value of the initial level of J. The values of the electric (S& dipole linestrengths were evaluated using the formula S, = e*

x

C2,(~JklXII~fJ’)2

(7)

X=2,4,6

(5) The matrix elements on the right-hand side of eqn (5) were taken from the table of Nielson and Koster [ 131.The matrix elements of eqn (5) were then transformed by the LS basis states to the physical coupling scheme, prior to being squared and substituted into eqn (3). The values of the six J symbols on the right-hand side of eqn (5) were taken from the tables of Rotenberg et al. [14]. The squared values of the reduced matrix elements CIAwere thus calculated. Using feXp for fed, the values of Th parameters were evaluated by the least-squares methods and were converted into Llhas has been explained in eqn

where n= A

(&,, X 102’), transition

Emission transition

x = (ai + 2)* 9nd

and Q,=[1.085

‘4%n -

97iz

-

6F~/z

-

%n

-

6H~v2

-

6H~~n

5.371 I 0.0442 20.6917 3.3332 0.2398 0.3902 32.4379

1.2466

A

1493 18 10,748 1983 210 465 50,390 2768

x lO”.x]-‘(u+1)~-~

(8)

where

fhr*rnc

-=

3h

1.085 X 10”

probabilities (A s-l), branching ratios @a%), relaxation rates (AT SC’) and relative lifetimes (TR)for Sm” doped glasses

Glass A &d

-’

where

(8). Table 4. Linestrengths

3hx1 w+l)Th 8**mc

[

Glass B PR%

2 16 3 1 74 4 -

&i

4.8706 0.0408 18.7621 3.0224 0.2204 0.3537 29.4148 1.3090

A

Glass C ORa

1334 16 1771 190 420 45,007 2989 -

2 16 3 1 73 5

&ai

2.1879 0.0407 8.3646 1.3454 0.2239 13.3205 1.3283 -

A

I%% 604

16 4312 794 195 428 20,537 773

2 16 3 I 1 74 3 rlA

AT Tr (as)

68,075 14.6

61,325 16.3

27.660 36.1

Absorption

Table 5. Linestrengths

(Sd X 10zo),

and photoluminescence

spectra of rare earth glasses

343

transition probabilities (A s-l), branching ratios @a%), relaxation rates (ATs-‘) and relative lifetimes (Ta) for Dy3+ doped glasses

Emission

Glass A

transition

Glass B

&d

A

bR%

scd

A

bR%

&d

A

OR%

I.1483 I.1642 0.8791 2.2521 I.4418 1.3384 I .0067 I .9602 13.2766 2.1 I75

II6 I84 I74 588 382 483 367 1054 10,921 2980 17,249 57.9

I I I 3 3 3 2 6 63 I7

5.0054 4.9209 3.8548 9.3764 6.4849 5.7219 4.1353 8.3259 52.625 I 5.9717

504 766 753 2410 1691 2034 1485 4409 42,634 8278 64,964 15.3

I I I 4 2 3 2 7 66 I3

I .6697 I.0618 0.7954 2.0867 I .3862 I .52635 I.10613 2.7003 16.6257 I.7018

I68 167 I57 540 364 547 400 I441 13,572 2377 19,733 50.6

I 1 1 3 2 3 2 7 68 12

A computerised least-squares fitting analysis from the measured absorption band intensities determines the best fit phenomenological parameters (Cl,, CL,and &,). These parameters are popularly known as Judd-Ofelt intensity parameters which characterise absorption band intensities of the glass under report. On examining the results concerning Judd-Ofelt intensity (Q,) parameters, the trends shown in Tables l-3 could be observed.

3.4. Optical transition probabilities

3.42. Property(ii). The fluorescence branching ratio (/3,~) for transition from an initial manifold (SW) to (S’L’J’) lower levels

Fig. 5(a)-(c) (for Dy3+ glasses)

Fig. 6(a)-(c) (for Eu’+ glasses)

4GV2 + -

6H5n

4F912 -

‘D, + ‘Fr

6H7f2

-

f3-l IJR

-

‘F:,

‘Do + ‘Fr

6H9iz

3.4.1. Property (i). The spontaneous emission probability from an initial manifold (SW) to a final manifold (S’L’J’) 647r4e2v3

AWW; WL’J’)I = 3htu + 1)nd

Table 6. Linestrengths

where the sum is over all possible terminal manifolds. 3.4.3. Property (iii). The radiative lifetime is given

(14

AT Tr (PS)

‘F6 ‘FS ‘Fe ‘F, ‘Fr ‘F,

+

2)2

A(SLJ); (S’L’J’)

S’L’J’

0.7198 3.2403 12.9613 16.679 I.7051 5.6024

=A;’

(11)

The values of spontaneous probabilities A (s-l), total transition probabilities AT (s-l) and radiative lifetime kW.r tmXitiOnS (T,), electric dipole linestrengths (s,d) and branching ratios (PRO/o)are presented in Tables 4, 5 and 6. 3.4.4. Property(iv). The induced emission cross-section up has been measured for the different emission bands using the following expression

h4 @p, = PA 87rcn;Ax

(9)

Glass B

AT

‘D, + --t -

(ni 7

1 -I

x

Glass A

0.7198 IO.801 I 6.8203

(10)

(S’L’J’)

probabilities (A s-l), branching ratios (@a%), relaxation lifetimes (TR)for Eu.” doped glasses

transition

T,

A[(SLJ); (S’L’J’)]

(Sd X 10za), transition

Emission

‘Do - ‘F6 - ‘F., --t ‘Fr

1

by

Fig. 4(a)-(c) (for Sm’+ glasses)

6H13R

A[(SZ.J); (S’L’J’)]

Pu =

The following fluorescence bands were observed for the three types of rare earth doped glasses.

-

Glass c

(12)

rates (Ar s-‘) and relative

Glass C

A

L&t%

hd

A

OR%

&d

A

PR%

33 789 708 1530 635.5 48 269 1319 2027 204 880 4783 209

2 52 46

0.7263 38.6349 6.2205

I 81 18

0.7375 55.9517 3.3975

I .0895 11.5904 46.3618 38.239 I .5552 5.1097

1 8 41 41 2 7

1.1062 16.787 I 67.1486 48.7699 0.8493 2.7978

34 4057 350 4441 224.6 24 461 2261 1961 40 145 4892 204.4

I 91 8

I 6 28 42 5 I8

33 2780 363 3449 289.9 24 316 1549 1526 72 264 3750 266.6

I 9 46 40 I 3

C. V. REDDY et al.

1 I

‘t$

lb) ‘G -

%

2

:

SSO

(bl ‘G -

6Hp

%

2

600 Wavden#h

(nm)

(a w N

550

600

650

WafeIergnl hm) Fig. 4. (a) Photoluminescence spectrum of Sm”* doped Glass A. (b) Photoluminescence spectrum of Sm’+ doped Glass B. (c) Photoluminescence spectrum of Sm’+ doped Glass C.

where X, is the peak fluorescence wavelength (nm) of the emission band and AX is the fluorescence band width determined by integrating the fluorescence line shape and dividing by the intensity at X,, c is the velocity of light, nd is the refractive index of glass and A is the transmission probability of the emission level. The measured values of emission wavelengths (X,) and band widths

(Ah) and stimulated emission cross-section (a,) for the glasses studied are summarised in Tables 7,8 and 9. By looking at the absorption and photoluminescence spectra (Figs l-6) it is more clear that Li+ ion containing glasses have shown brighter absorption profiles and stronger emissions compared to those with Na+ ions and the (Lif + Na+) glass system. In all the above

Table 7. Measured emission peak wavelength X, (nm), half band width AX (nm) and stimulated emission cross-section (up X ION cm2) for SmS+ glasses Glass B

Glass A Transition

4Gsi7 -

%n

- 6H,n - %n

A, 563.2 599 645

A,x 8 8 II

Glass C

UP

A,

AX

OP

A,

Ah

00

-

564.2 600.6

IO.5 II

-

563.6 599.8

IO II

0.248

649.6

11.5

19.080

645.6

II

8.859

1.2136 21.604

0.968

Absorption and photoluminescence spectra of rare earth glasses

650

950

500

650

600

Fig. 5. (a) Photoluminescence spectrum of Dy.” doped Glass A. (b) Photoluminescence spectrum of Dy3+ doped Glass B. (c) Photoluminescence spectrum of Dy3+ doped Glass C.

Table 8. Measured emission peak wavelength X, (nm), half band width AX (nm) and stimulated emission cross-section (up X 10zo cm’) for Dy3+ glasses Glass B

Glass A

Glass C

Transition

A,

Ahx

UP

hP

AA

UP

AP

AX

UP

4F 9f2 -

575

16 I8

2.033 0.2463

515 484

I5 I7

8.5068 0.7316

575.4 483

I5 I7

2.7091 0.2078

‘H,3/2

- ‘H ISR

483.4

Table 9. Measured emission peak wavelength A, (nm), half band width Ah (nm) cm*) for Eu3+ glasses Glass

Transition

hP

AX

5D, 4 ‘F2 - ‘F3 ‘Do 4 ‘Fz

579 591.4 612.2

3.5 9.5 IO

and stimulated emission cross-section (a, X 10”

Glass B

A UP

I .465 7.022 1.890

Glass C

XP

Ah

QP

XP

AX

fJP

579.6 591.0 612

3.5 12 IO

1.940 10.922 2.488

579.4 591.2 612.4

4 12 IO

I .22 8.889 I.571

C. V. REDDY et al.

I (Ws

c

f

I f 600

650

700

Wavdrn@(ti

Wauakngm(Iyn)

Fig. 6. (a) Photoluminescence spectrum of Eu3+ doped Glass A. (b) Photoluminescence spectrum of Eu3+ doped Glass B. (c) Photoluminescence spectrum of Eu3+ doped Glass C. three types of glasses, it is significant to note that Li+ containing glasses are uniformly demonstrating better results over the other two; therefore, it is concluded that the optical efficiency of borotelhuite glasses has been improved by the addition of Lif content in the glass matrices used in the present work. Because of the fact that these Li+ containing glasses are showing extended UV (350 nm) and IR transmission (4.5 pm) compared to the other two combinations, they would be developed further in bulk. Thus we have verified the applicability of the JuddOfelt theory in understanding both absorption and emission properties of rare earth doped borotellurite glasses. Acknowledgements-The author is grateful to Mr. K. Rajamohan Reddy, Mr. Sooraj Hussain & Dr. K. Annapuma for their full cooperation and support in this work.

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44A, 1381. 11. Judd, B.R.. Phys. Rev., 1X2,127,750. 12. Ofelt, G.S.,J. Chem. Phys., 1%2.37,511. 13. Nielson, C.W. and Koster, G.F., Spectroscopic Coeficienrs forp”, d” andf’ Conjgurotion, MITPress, Cambridge, MA,

1964. 14. Rotenberg, M., Bivins, R., Metropolis, N. and Wooten, J. R., The 35 and 65 Symbols, MIT Press, Cambridge, MA, 1959.