Visible luminescence characteristics of Dy3+-doped LBTAF glasses

Journal of Alloys and Compounds 474 (2009) 382–387

Contents lists available at ScienceDirect

Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom

Visible luminescence characteristics of Dy3+ -doped LBTAF glasses B.C. Jamalaiah a , J. Suresh Kumar a , T. Suhasini a , Kiwan Jang b , Ho Sueb Lee b , Hyukjoon Choi c , L. Rama Moorthy a,∗ a

Department of Physics, Sri Venkateswara University, Tirupati 517502, India Department of Physics, Changwon National University, Changwon, 641-773, Republic of Korea c Korea Institute of Curriculum & Evaluation (KICE), Seoul, 110-230, Republic of Korea b

a r t i c l e

i n f o

Article history: Received 10 April 2008 Received in revised form 16 June 2008 Accepted 24 June 2008 Available online 3 August 2008 Keywords: Amorphous materials Rare earth alloys and compounds Rapid solidification Quenching Optical properties Luminescence

a b s t r a c t The visible luminescence of Dy3+ -doped lead borate titanate aluminium fluoride (LBTAF) glasses has been investigated. The observed energy levels of 1.0 mol% Dy2 O3 -doped LBTAF glass have been fitted to the well-known free-ion Hamiltonian (HFI ) model. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters ˝t (t = 2, 4 and 6) were evaluated using least square fit. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetime and branching ratios were calculated for 4 F9/2 excited level. Room temperature fluorescence spectra for different concentrations of Dy3+ -doped LBTAF glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy3+ emission spectra increases with increasing concentration of 0.1, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measured branching ratios are reasonably high for transitions 4 F9/2 → 6 H15/2 and 6 H13/2 suggesting that the emissions at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. © 2008 Elsevier B.V. All rights reserved.

1. Introduction The development of new optical glasses has revolutionized the electronics and the telecommunication industries. Spectroscopic investigation of rare-earth ions in glassy matrices exhibit characteristic properties for potential applications as laser materials. Rare-earth-doped glasses provide better opportunities for tuning and Q-switching because of their wide emission cross-sections than crystal lasers [1]. In the visible region, Dy3+ exhibit bright blue and yellow emissions corresponding to 4 F9/2 → 6 H15/2 and 6 H13/2 transitions respectively along with feeble red emission corresponding to 4 F9/2 → 6 H11/2 transition. The lasing action in the visible region finds wide technological applications in commercial display sensors [2]. Basically lead oxide glasses possess high chemical stability, refractive indices and spontaneous emission probabilities [3]. In general, borate glasses have lower thermal expansion coefficients and higher densities than other oxide glasses. Hence, there exists stronger bonding and denser packing in borate glasses [4]. The addition of AlF3 improves the optical quality [5] with a tendency to devitrify during cooling because of the strong ionic bonding. Addition of fluoride content also decreases the phonon energy and

increases the moisture resistance and transparency in visible region [6]. Host materials having low phonon energies are highly useful for obtaining high efficiency lasers and fiber amplifiers [7]. Titanium is a common constituent of ceramics and glasses which acts as a glass former at low concentrations [8]. Due to high mechanical resistance and stability in several corrosive environments, TiO2 can be used as a novel host material for rare-earth ions [9]. Recently, titanium-doped silica played a crucial role in the development of optical fibers [10]. The present work reports the spectroscopic investigation of visible luminescence of Dy3+ -doped lead borate titanate aluminium fluoride (LBTAF) glasses to ascertain their utility for solid-state laser devices. 2. Experimental details 2.1. Glass preparation The glass samples were prepared with chemical composition of (50 − x) PbO + 30 H3 BO3 + 10 TiO2 + 10 AlF3 + x Dy2 O3 (where x = 0.1, 0.5, 1.0 and 2.0 mol%). Homogeneous mixture of reagent grade PbO, H3 BO3 , TiO2 , AlF3 and Dy2 O3 were melted in an electric furnace at 1050 ◦ C in porcelain crucible for about 1 h. The melt was poured into pre-heated brass moulds and annealed at 360 ◦ C for 8 h to remove thermal strains. The glass samples were slowly cooled to the room temperature, cut into square shape and polished for optical studies. 2.2. Physical properties

∗ Corresponding author. Tel.: +91 877 2249666x272; fax: +91 877 2225211. E-mail address: [email protected] (L. Rama Moorthy). 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.06.094

For concentration determination, density measurements were made by the Archimedes’s method using xylene as the immersion liquid. Refractive index (1.595)

B.C. Jamalaiah et al. / Journal of Alloys and Compounds 474 (2009) 382–387 was measured with an Abbe’s refractometer (Model: GE-138) with sodium vapour lamp using 1-bromonapthalene as contact liquid. From the measured values of sample thickness (0.276 cm) and density (5.60 g/cm3 ), the rare-earth ion concentration (0.733 mol/l) was estimated for 1.0 mol% of Dy2 O3 -doped LBTAF glass.

383

and J is the total angular momentum of the initial state. The electric dipole transition line strength is given by



Sed [(S, L)J; (S 1 , L1 )J 1 ] =



2

˝t < (S, L)J||U t ||(S 1 , L1 )J 1 >

(6)

t=2,4,6

2.3. Optical studies Room temperature optical absorption spectra were recorded using Varian Cary 5E UV-VIS-NIR spectrophotometer in the wavelength range 600–2000 nm. The excitation and visible luminescence spectra were recorded using Fluorolog (JOBIN YVON 21) spectrofluorometer with xenon flash lamp as source.

where ˝t (t = 2, 4, 6) represent the J–O intensity parameters of rareearth ion in a particular given glass matrix and ||Ut || are the doubly reduced matrix elements of rank ‘t’. The magnetic dipole transition linestrength is given by [12,13]:

3. Theory

Smd [(S, L)J; (S 1 , L1 )J 1 ] =

3.1. Energy level analysis

< (S, L)J||(L + 2S)||(S 1 , L1 )J 1 > |2

The following free ion Hamiltonian (HFI ) model has been used to study the energy level structure of Dy3+ ion [11]: HFI = EAVG +

+





F k fk + so Aso + ˛L(L + 1) + ˇG(G2 ) + G(R7 )

k

T i ti +



i

P k pk +



k

M j mj

(1)

j

where k = 2, 4, 6; i = 2, 3, 4, 6, 7, 8 and j = 0, 2, 4. The free-ion Hamiltonian includes central field parameter (EAVG ), two body electrostatic interactions (Fk ), spin-orbit interaction ( so ), two body configuration interactions (˛, ˇ, ), three body configuration interactions (Ti ), electrostatically correlated spin–orbit interaction (Pk ) and spin–other orbit interaction (Mj ). The fitting procedure between experimental and calculated energy level values was carried out using the standard least-square method. The quality of the fit was given by the root mean square deviation  as follows:



rms =

(Ei

exp

)

(2)

The radiative transition probability (AR ), radiative lifetime ( R ) and branching ratio (ˇR ) which predict the fluorescence intensity of the lasing transition were calculated using the J–O intensity parameters (˝t ). The radiative transition probability (AR ) for emission from an initial state (S, L)J to a final state (S1 , L1 )J1 is given by 644 e2 AR [(S, L)J; (S , L )J ] = 3h(2J + 1)3 1

3.2. Oscillator strengths and J–O parameters

AT [(S, L)J] =



fexp = 4.32 × 10−9

2

∈ () d

(3)

1

where ∈() is the molar absorption coefficient corresponding to the energy ( cm−1 ) and d is the half-bandwidth of the absorption band. From the Beer–Lambert law the molar absorption coefficient at a given energy  is expressed as ∈ () =

1 log Cl

I  0

(4)

I

where C is the concentration of rare-earth ion in mol/l, l is the optical path length and log (I0 /I) is the optical density. The theoretically calculated oscillator strengths (fcal ) of transitions between an initial J manifold (S, L) J and a final J1 manifold (S1 , L1 ) J1 were estimated using the Judd–Ofelt (J–O) expression [12,13]: fexp = fcal [(S, L)J; (S 1 , L1 )J 1 ] =

82 mc 3h(2J + 1)



2

(n2 + 2) Sed + nSmd 9n



(5) where m is the mass of the electron, h is the Planck’s constant, n is the refractive index,  is the mean energy of the transition in cm−1

1



n(n2 + 2) Sed + n3 Smd 9



(8)



AR [(S, L)J; (S 1 , L1 )J 1 ]

(9)

(S 1 ,L1 )J 1

The radiative lifetime  R of the emission state (S, L)J is given by R =

1 AT [(S, L)J]

(10)

The fluorescence branching ratio ˇR can be written as ˇR =

The experimentally determined oscillator strengths (fexp ) are calculated using the relation:

1

where [n(n2 + 2)2 /9] is the Lorentz local field correction factor for electric dipole transition [14]. The total radiative emission probability AT [(S, L)J] of an excited state is the sum of the AR [(S, L)J; (S1 , L1 )J1 ] terms calculated overall final states (S1 L1 )J1 and is given by [15]:

exp

where Ei and Eical are the experimental and calculated energies for level i and N represent the total number of levels included in the energy level fit.

(7)

3.3. Radiative properties

cal 2

− Ei N

h2 | 162 m2 c 2

AR [(S, L)J; (S 1 , L1 )J 1 ] AT [(S, L)J]

(11)

The stimulated emission cross-section between the (S, L)J and (S1 , L1 )J1 emission levels is given as e [(S, L)J; (S 1 , L1 )J 1 ] =

4p 8cn2 eff

AR [(S, L)J; (S 1 , L1 )J 1 ]

(12)

where p is the peak fluorescence wavelength and eff is the effective linewidth, which can be calculated by integrating the intensity of the luminescence lineshape and dividing it by the intensity at the peak wavelength (p ) using the relation [14]:



eff =

I d Ip

(13)

4. Results and discussion 4.1. Absorption spectra and free-ion parameters Room temperature NIR absorption spectrum of 1.0 mol% Dy3+ : LBTAF glass shown in Fig. 1 is similar to other Dy3+ ion-doped glasses [15]. The spectra consists of six peaks at 1684, 1277, 1095, 900, 798 and 753 nm corresponding to 6 H15/2 → 6 H11/2 ; (6 F11/2 + 6 H9/2 ); (6 F9/2 + 6 H7/2 ); 6 F7/2 ; 6 F5/2 and 6 F3/2 transitions respectively. The identification and assignment of energy levels

384

B.C. Jamalaiah et al. / Journal of Alloys and Compounds 474 (2009) 382–387 Table 2 Experimental and calculated oscillator strengths for 1.0 mol% Dy2 O3 -doped LBTAF glass Transition

H15/2 → 6 H11/2 6 F11/2 + 6 H9/2 6 F9/2 + 6 H7/2 6 F7/2 6 F5/2 6 F3/2 6

Oscillator strength (×10−6 ) fexp

fcal

1.09 6.13 1.93 1.61 0.97 0.18

1.11 6.13 1.92 1.66 0.81 0.15  rms = ±0.072

Fig. 1. Room temperature NIR absorption spectrum of 1.0 mol% Dy3+ ion-doped LBTAF glass.

have been done according to our earlier report [16]. The observed energy levels are fitted to the free-ion Hamiltonian model by diagonalizing the energy matrices of 4f9 electronic configuration. The fitting procedure has been done by varying the well-optimized initial parameters Fk ,  so , ˛, ˇ and  of Dy3+ : LaCl3 [17]. In all the fits Ti (i = 2, 3, 4, 6, 7, 8); Mj (j = 0, 2, 4) and Pk (k = 2, 4, 6) parameters were fixed to the values of Dy3+ : LaCl3 by constraining the parameters M2 = 0.56 M0 , M4 = 0.38 M0 , P4 = 0.75 P2 and P6 = 0.50 P2 , respectively. Experimentally determined and theoretically calculated energies along with various spectroscopic parameters derived from least square fit calculations of Dy3+ ions in LBTAF glass are given in Table 1. The root mean square deviation ( rms ) ± 57 cm−1 , calculated by using Eq. (2) shows a good fit between the observed and calculated energy levels and is comparable with other Dy3+ ion-doped glass systems [16,18–20]. The parameter EAVG is the uniform energy shift of the entire configuration, which represents the spherically symmetric electron contribution. The values of hydrogenic ratios F2 /F4 and F2 /F6 indicate that the radial integral parts of the f-orbital of Dy3+ ions remain unchanged due to the shielding of the 4f shells by 5s2 and 5p6 orbitals. 4.2. Oscillator strengths—intensity parameters The intensity of an absorption band is expressed in terms of its oscillator strength [15]. The experimentally determined oscilTable 1 Experimental and calculated energies along with the free-ion parameter values for 1.0 mol% Dy3+ ion-doped LBTAF glass Energy level

6

H15/2 6 H13/2 6 H11/2 6 H9/2 6 F11/2 6 F9/2 6 H7/2 6 H5/2 6 F7/2 6 F5/2 6 F3/2

Energy (cm−1 )

Free-ion parameters (cm−1 )

Eexp

Ecal

Parameter

Value

0 – 5,937 – 7,833 – 9,133 – 11,118 12,531 13,282

18 3,564 5,881 7,743 7,846 9,088 9,166 10,215 11,082 12,526 13,307

EAVG F2 F4 F6 ˛ ˇ   k F F2 /F4 F2 /F6

55375 93120 65505 41822 7.46 −608 1774 1945 200447 1.42 2.22

 rms = ±58

lator strengths (fexp ) have been evaluated by measuring the areas under the absorption bands using Eq. (3). Theoretically calculated oscillator strength (fcal ) of electric dipole transition between an initial manifold (S, L)J and final manifold (S1 , L1 )J1 within the 4f9 configuration can determined using J–O intensity parameters, which are the characteristic of a given rare-earth ion in a given matrix. The best set of J–O intensity parameters, ˝2 = 7.05 × 10−20 ; ˝4 = 1.22 × 10−20 and ˝6 = 1.91 × 10−20 cm2 are evaluated by least square fit method using the experimental oscillator strengths (fexp ), theoretical oscillator strength (fcal ) (Eq. (5)) and the doubly reduced matrix elements ||Ut ||2 . Measured and theoretically calculated oscillator strengths are presented in Table 2 for 1 mol%. Dy3+ iondoped glass. The small  rms value of ±0.072 × 10−6 indicates a good fit between calculated and measured oscillator strengths and the best set of intensity parameters. In general, J–O parameters provide an insight into the local structure and bonding in the neighborhood of RE3+ ions. The magnitude of structure/environment parameter, ˝2 depends on covalency of metal ligand bond and also explains the asymmetry of ion sites in the vicinity of rare-earth ions. In the present case the higher magnitude of ˝2 results the decrease of covalent bonding and suggests that the rare-earth ion site has lower asymmetry in LBTAF glass host. The ˝6 is inversely related to the rigidity of the host and also vibronic dependent [21]. The magnitude of ˝6 = 1.91 × 10−20 cm2 indicates the higher rigidity of present LBTAF glass host than other reported systems [22–25]. Certain absorption transitions of each rare-earth ion are very sensitive to the host environment and ion concentration due to the inhomogeneity of the ligand environment [26]. Such transitions are known as hypersensitive transitions obeying the selection rules S = 0, | L| ≤ 2 and | J| ≤ 2 [27]. The hypersensitive transitions are associated with the large values of oscillator strengths as well as reduced matrix element ||U2 ||2 . As seen from Table 2, for Dy3+ , the hypersensitive transition is 6 H15/2 → (6 F11/2 + 6 H9/2 ) possessing maximum value of oscillator strength (fexp ) which is solely dependent on the ˝2 value and also sensitive to the local symmetry of ligand field or covalent bond of Dy3+ ion in the host [27]. The spectroscopic quality factor X = ˝4 /˝6 , is one of the important lasing characteristic parameter for predicting the stimulated emission in any active medium. Dy3+ ion-doped glass hosts having the range of spectroscopic quality factors 0.42–1.92 are the good candidates for laser active media [28]. The reasonably high value of spectroscopic quality factor X = 0.64, predicts efficient stimulated emission in the present host. Table 3 presents the comparison of J–O intensity parameters, their trend and spectroscopic quality factors of Dy3+ ions in LBTAF glass with different hosts. 4.3. Fluorescence spectra Fig. 2 presents the emission spectra of 0.1, 0.5, 1.0 and 2.0 mol% of Dy3+ -doped LBTAF glasses obtained with the excitation wave-

B.C. Jamalaiah et al. / Journal of Alloys and Compounds 474 (2009) 382–387

385

Table 3 Comparison of J–O parameters, their trends and spectroscopic quality factors of Dy3+ ions in LBTAF glass with different hosts Glass system

LBTAF [This work] ZBLA [22] ZBLALi [23] 20Na2 O + 80TeO3 [24] 35ZnO + 65TeO3 [24] 15BaO + 85TeO3 [24] Fluorohafnate [25]

J–O parameters (×10−20 cm2 ) ˝2

˝4

˝6

7.05 3.22 2.70 3.70 4.30 3.20 3.12

1.22 1.35 1.80 1.15 1.32 1.35 2.07

1.91 2.38 2.00 2.22 2.53 2.47 2.48

Trend

Spectroscopic quality factor X = ˝4 /˝6

˝2 > ˝4 > ˝6 ˝2 > ˝4 > ˝6 ˝2 > ˝4 > ˝6 ˝2 > ˝4 > ˝6 ˝2 > ˝4 > ˝6 ˝2 > ˝4 > ˝6 ˝2 > ˝4 > ˝6

0.64 0.56 0.90 0.52 0.52 0.55 0.83

Fig. 2. Room temperature fluorescence spectra for different concentrations of Dy3+ ion-doped LBTAF glasses (inset figure represents the excitation spectra for 1.0 mol%).

length of 386 nm. The spectra show three emission peaks at 484, 576 and 664 nm corresponding to 4 F9/2 → 6 H15/2 ; 6 H13/2 and 6 H11/2 transitions, respectively. The excitation spectra of 1.0 mol% of Dy3+ doped LBTAF glass can also be seen in the inset of Fig. 2 with an intense peak at 386 nm corresponding to 6 H15/2 → 4 I13/2 transition. The red emission at 664 nm is very feeble, while the blue and yellow emissions at 484 and 576 nm are more intense. The peak emission intensities of Dy3+ in LBTAF glasses increase with concentration from 0.1 to 1.0 mol% and beyond that decreases. This clearly indicates the effect of concentration quenching on luminescence in this host. It is also observed that the luminescence spectra obtained with the excitation wavelength of 386 nm are similar to the spectra obtained, when excited with 450 nm corresponding to the 6 H15/2 → 4 I15/2 transition. The fluorescence intensity of 4F 6 4 6 9/2 → H15/2 transition is slightly higher than F9/2 → H13/2 and this may be due to the addition of AlF3 , that improves the optical quality and also decrease the phonon energy of the host [5,6]. The energy level diagram of Dy3+ shown in Fig. 3 indicates that the excitation with 386 nm populates excited manifold state 4 F9/2 by non-radiative transitions from upper states and decays radiatively to 6 H15/2 , 6 H13/2 and 6 H11/2 , respectively. From the emission spec-

Fig. 3. Partial energy level diagram of Dy3+ ion in LBTAF glass.

tra of different concentrations of Dy3+ ion in LBTAF glasses (Fig. 2), the peak wavelengths (p ), effective linewidths ( eff ), peak emission cross-sections ( e ) and measured branching ratios (ˇmes ) are determined for 4 F9/2 → 6 H15/2 (484 nm) and 4 F9/2 → 6 H13/2 (576 nm) transitions and are presented in Table 4. Normally the most potential laser transitions possess large stimulated emission ( e ) cross-section [29]. The peak emission cross-section of 26.13 × 10−22 cm2 for 4 F9/2 → 6 H13/2 transition is quite high and found comparable with the other reported systems [30]. Theoretically, the radiative process in Dy3+ : LBTAF glasses has been explained by the J–O model in which only electric dipole transitions are taken into consideration [31], since the magnetic dipole contribution is negligibly small. The calculated J–O parameters of 1.0 mol% Dy2 O3 -doped glass have been are used to estimate the radiative transition rates (AR ), fluorescence branching ratios (ˇR )

Table 4 Comparison of measured values of effective linewidths ( eff ), peak emission cross-sections ( e ) and branching ratios (ˇmes ) for 4 F9/2 → 6 H15/2 (484 nm) and 4 F9/2 → 6 H13/2 (576 nm) transitions in different concentrations of Dy3+ ion in LBTAF glasses Rare-earth ion concentration (mol%)

0.1 0.5 1.0 2.0

4

F9/2 → 6 H15/2

4

F9/2 → 6 H13/2

eff (nm)

 e (×10−22 ) (cm2 )

ˇmes

eff (nm)

 e (×10−22 ) (cm2 )

ˇmes

18.12 18.03 17.60 18.02

2.56 2.56 2.62 2.56

0.54 0.55 0.55 0.55

16.63 15.89 15.69 15.86

24.65 25.80 26.13 25.85

0.45 0.44 0.44 0.44

386

B.C. Jamalaiah et al. / Journal of Alloys and Compounds 474 (2009) 382–387

Table 5 Radiative transition probabilities (AR ), branching ratios (ˇ) and radiative lifetimes ( R ) estimated for selected states of 1.0 mol% of Dy3+ ion in LBTAF glass Transition

AR (s−1 )

F9/2 → 6 F3/2 6 F5/2 6 F7/2 6 F9/2 + 6 H7/2 6 F11/2 + 6 H9/2 6 H11/2 6 H13/2 6 H15/2

0 8 9 12 19 84 714 161

4

AT =



AR = 1007

 e (×10−22 cm2 )

Branching ratios ˇcal

ˇmes

0.000 0.007 0.008 0.011 0.017 0.076 0.647 0.146

– – – – – 0.007 0.439 0.554

– – – – – 9.98 26.13 2.62

 R = 993 ␮s

and the stimulated emission cross-sections ( e ) from the excited manifold 4 F9/2 to the lower lying manifolds and are presented in Table 5. It can be seen from Table 5, the predicted branching ratios from an upper to lower manifolds suggest that there exists one value of the branching ratios significantly higher than the rest. However, for 4 F9/2 → 6 H15/2 and 6 H13/2 transitions the predicted branching ratios are found to be 15% and 65%, whereas the measured branching ratios are 55 and 44%, respectively. The variation between the predicted and measured branching ratios may be due to the presence of fluoride content that decreases the phonon energy [7] in the present glasses. The host materials with low phonon energies have been used for obtaining high efficiency lasers and fiber amplifiers [1]. The evaluated radiative emission parameters namely the transition rates (AR ), branching ratios (ˇR ) and stimulated emission cross-sections ( e ) suggest that 1.0 mol% Dy2 O3 -doped glasses may be used for two emission channels in blue (484 nm) and yellow (576 nm) regions. 4.4. Radiative lifetimes The 4 F9/2 → 6 H13/2 (576 nm) decay curves for different concentrations of Dy3+ -doped LBTAF glasses excited by 386 nm wavelength are shown in Fig. 4. It has been observed that for all the concentrations, the decay profiles are nearly single exponential. The radiative lifetime calculated from the J–O analysis is 993 ␮s. The measured lifetimes are found to be 246, 302, 395 and 166 ␮s for 0.1, 0.5, 1.0 and 2.0 mol% concentrations, respectively. The measured lifetimes increases with increasing concentration showing maximum for 1 mol% and beyond 1 mol% the lifetimes decreases due to

concentration quenching. The difference between the experimental and calculated lifetimes may be due to multiphonon relaxation and cross relaxation [32]. The estimated multiphonon relaxation rate, using the following equation [33] is 1.53 × 103 s−1 . WMP =

1 1 − meas R

(14)

where  mes and the  R are the measured and calculated lifetimes(s), respectively. The presence of fluoride content reduces the phonon energy of the host and hence increases the lifetime of the fluorescent level by decreasing the non-radiative decay due to multiphonon relaxation [34]. The quantum efficiency , which is one of the important laser parameters can be evaluated using the equation [35]:

=

mes emitted light power = R absorbed radiation power

(15)

The quantum efficiency of 0.40 evaluated for 4 F9/2 → 6 H13/2 transition in 1.0 mol% of Dy3+ -doped LBTAF glass is approximately half of the other Dy3+ ion-doped glass hosts [16,31]. 5. Conclusions The visible luminescence characteristics of Dy3+ ion in LBTAF glasses have been analyzed. J–O analysis explains the evidence of relatively high values of the ˝2 and ˝4 parameters as a consequence of the high oscillator strength of the hypersensitive transition 6 H15/2 → (6 F11/2 + 6 H9/2 ). The magnitude of spectroscopic quality factor X = 0.64 predicts large stimulated emission cross-section in the present host. The large stimulated emission cross-section of 26.13 × 10−22 cm2 for 4 F9/2 → 6 H13/2 transition corresponding to 576 nm supports that the present glass host is a good candidate for laser active material. The decay profiles of the visible luminescence are found to be single exponential for different concentrations of Dy3+ ion. Acknowledgements This research work was partially supported by the Korea Research Foundation Grant KRF-J00902. One of the authors Prof. L. Rama Moorthy greatly acknowledges the financial support from DRDO (No. ERIP/ERJ0603593/M/Ol/984), Government of India, New Delhi for the sanction of major research project to carry out the present work. References

Fig. 4. The 4 F9/2 → 6 H13/2 (576 nm) decay curves for different concentrations of Dy3+ doped LBTAF glasses.

[1] J.A. Savage, Mater. Sci. Rep. 2 (1987) 99–137. [2] D.P. Machewirth, K. Wei, V. Krasteva, R. Datta, E. Snitzer, G.H. Sigel Jr., J. NonCryst. Solids 213 (1997) 295–303. [3] L.C. Courrol, L.R.P. Kassab, V.D.D. Cacho, S.H. Tatumi, N.V. Wetter, J. Lumin. 102 (2003) 101–105. [4] G.A. Kumar, P.R. Biju, N.V. Unnikrishnan, Phys. Chem. Glasses 40 (1999) 219–224. [5] S.J.L. Ribeiro, Ph. Goldner, F. Auzel, J. Non-Cryst. Solids 219 (1997) 176–181. [6] L. Zhang, L. Wen, H. Sun, J. Zhang, L. Hu, J. Alloys Compd. 391 (2005) 156–161. [7] Y.G. Choi, J. Heo, J. Non-Cryst. Solids 217 (1997) 199–207. [8] D.Y. Smith, C.E. Black, C.C. Homes, E. Shiles, Phys. Status Solidi C 4 (2007) 838–842. [9] R. Palomino-Merino, A. Conde-Gallardo, M. Garcia-Rocha, I. HernandezCalderon, V. Castano, R. Rodriguez, J. Thin Solid Films 401 (2001) 118–123. [10] J. Hecht, City of Life, Oxford University Press, London, 1999, pp. 134–146. [11] W.T. Carnall, P.R. Fields, K. Rajak, J. Chem. Phys. 49 (1968) 4424–4442. [12] B.R. Judd, Phys. Rev. B 127 (1962) 750–761. [13] G.S. Ofelt, J. Chem. Phys. 37 (1962) 511–520. [14] G.A. Kumar, A. Martinez, E. De La Rosa, J. Lumin. 99 (2002) 141–148. [15] M.B. Saisudha, J. Ramakrishna, Phys. Rev. B 53 (1996) 6186–6196. [16] M. Jayasimhadri, L.R. Moorthy, K. Kojima, K. Yamamoto Norikowada, J. Phys. D: Appl. Phys. 39 (2006) 635–641. [17] C.K. Jayasankar, F.S. Richardson, M.F. Reid, J. Less Common Met. 148 (1989) 289–296.

B.C. Jamalaiah et al. / Journal of Alloys and Compounds 474 (2009) 382–387 [18] P. Nachimuthu, R. Jagannathan, V. Nirmal Kumar, D. Narayana Rao, J. Non-Cryst. Solids 217 (1997) 215–223. [19] C.K. Jayasankar, E. Rukmini, Physica B 240 (1997) 273–288. [20] S. Tanabe, T. Hanada, M. Watanabe, T. Hayashi, N. Soga, J. Am. Ceram. Soc. 78 (1995) 2917–2922. [21] C.K. Jorgensen, R. Reisfeld, J. Less Common Met. 93 (1983) 107–112. [22] J.L. Adam, A.D. Docq, J. Lucas, J. Solid State Chem. 75 (1988) 403–412. [23] V.M. Orera, P.J. Alonso, R. Cases, R. Alcala, Phys. Chem. Glasses 29 (1988) 59–62. [24] J. Hormadely, R. Reisfeld, J. Non-Cryst. Solids 30 (1979) 337–348. [25] R. Cases, M.A. Chamarro, J. Solid State Chem. 90 (1991) 313–319. [26] C.K. Jorgensen, B.R. Judd, Mol. Phys. 8 (1964) 281–290. [27] S. Tanabe, T. Ohyagi, N. Soga, T. Hanada, Phys. Rev. B 46 (1992) 3305–3310.

387

[28] D.K. Sardar, W.M. Bradley, R.M. Yow, J.B. Gruber, B. Zandi, J. Lumin. 106 (2004) 195–203. [29] B. Karthikeyan, S. Mohan, M.L. Baesso, Physica B 337 (2003) 249–254. [30] P. Babu, C.K. Jayasankar, Opt. Mater. 15 (2000) 65–79. [31] L. Nagli, D. Bunimovich, A. Katzir, O. Gorodetsky, V. Molev, J. Non-Cryst. Solids 217 (1997) 208–214. [32] Y.C. Ratnakaram, D. Thirupathi Naidu, R.P.S. Chakradhar, J. Non-Cryst. Solids 352 (2006) 3914–3922. [33] Y.G. Choi, V.A. Chernov, J. Heo, J. Non-Cryst. Solids 217 (1997) 199–207. [34] C.K. Jayasankar, V. Venkatramu, S. Surendra Babu, P. Babu, J. Alloys Compd. 374 (2004) 22–26. [35] V.K. Rai, S.B. Rai, J. Solid State Commun. 132 (2004) 647–652.