Poster

PowerPoint Presentation: 

International Conference on Recent Trends in Advanced Materials (ICRAM – 2012), VIT University, Vellore, 20-22 February 2012 C. Madhukar Reddy 1 , B. Sudhakar Reddy 2 , B. Deva Prasad Raju 3, * 1 Department of Physics, Sri Venkateswara University, Tirupati – 517 502, India 2 Department of Physics, Sri Venkateswara Degree College, Kadapa – 516 003, India 3 Department of Future Studies, Sri Venkateswara University, Tirupati – 517 502, India Structural and Luminescence studies of Tb 3+ ions Activated Lead containing Sodium Fluoroborate Glasses *Corresponding Author Details Dr . B. Deva Prasad Raju Associate Professor in Physics Department of Future Studies, Sri Venkateswara University, Tirupati - 517 502, India . Email: drdevaprasadraju@gmail.com ABSTRACT : Lead containing sodium fluoroborate glasses ( PbSFB ) with molar composition of 20PbO + 5CaO + 5ZnO + 10NaF + (60-x ) B 2 O 3 + xTb 2 O 3 , (x = 0.1, 0.5, 1.0, 1.5 and 2.0 mol%) were prepared and investigated by the FT-Raman optical absorption and fluorescence studies. The FT-Raman profile has revealed that the glass has both BO 3 and BO 4 units. The absorption transitions in the NIR region were assigned to different transitions from the 7 F 6 ground state to various excited states ( 7 F 1, 7 F 2 and 7 F 3 ). From the fluorescence spectra the observed transitions are 5 D 4 → 7 F 6 , 7 F 5, 7 F 4 and 7 F 3 . The transion 5 D 4 → 7 F 5 in the green wavelength region (547 nm) is more intense and has the applications in green light emitting phosphors, LEDs and lasers. EXPERIMENTAL Composition ( in mol %) 20PbO+5CaO+5ZnO+10NaF+(60-x)B 2 O 3 +xTb 2 O 3 ( x = 0.1, 0.5, 1.0, 1.5 and 2.0 mol% ) Method : Melt quenching Melting temperature : 950 O C, 1 hour Annealing temperature : 360 O C , 8 hours FT-Raman measurements : Bruker RFS 27 Raman Spectrometer Optical measurements : Perkin Elmer Lambda 950, Fluorolog-3 FT-RAMAN EXCITATION ENERGY LEVEL DIAGRAM LUMINESCENCE CONCLUSIONS Among the rare earth ions, the terbium (Tb 3+ ) ion is quite interesting due to nits blue and green emissions. Therefore these ar more useful in certain applications such as green phosphor or trichromatic fluorescent lamps, color television tubes. The FT-Raman data indicate the presence of trigonal BO 3 and tetrahedral BO 4 structural units in the glasses, the network structure being mainly built by: di -, tri-, tetra-, penta -, and ortho -, borate groups. Three absorption transitions( 7 F 6 → 7 F 1, 7 F 2 and 7 F 3 ) were observed at 5280, 5120, 4533 cm -1 in the NIR region. All the absorption transitions are due to electric dipole interaction following the selection rules, ΔS=0, | ΔL| ≤ 6, | ΔJ|≤ 6. Absorption cross-section is a measure for the probability of an absorption process, and is used to quantify the probability of a certain particle-particle interaction. The value of absorption cross section of 1.0 mol % Tb 3+ ion in PbSFB glass at 1895 nm is 3.84 Χ 10 -20 cm 2 , at 1950 nm is 3.81 Χ 10 -20 cm 2 , and at 2210 nm is 3.70 Χ 10 -20 cm 2 . The photoluminescence spectra of the Tb 3+ : PbSFB glasses show that the concentration of Tb 3+ ions increases the intensities of emission peaks originating from 5 D 4 state also increase. It is suggested that the Tb 3+ ions doped PbSFB glasses may be used as luminescent novel optical material for the development of lasers and photonic devices to emit green intense fluorescence at 547 nm corresponding to 5 D 4 → 7 F 5 transition. ABSORPTION The Raman band at 89 cm -1 is associated to the BO 3 -PbO 4 bridged local collective vibrations. The 475 cm -1 ­ band is assigned to a ring angle bending (B-O-B), which is observed at 470 cm -1 for pure B 2 O 3 . The bands located at 635 and 720 cm -1 are related to the chain and ring type meta borate groups. The occurrence of band at around 903 cm -1 is an indication of the presence of pentaborate groups in the borate glasses. The band centered at 1269 cm -1 is assigned to pyroborate groups. The bands in the region 1300-1600 cm -1 is similar to that in the Raman spectra of large number of modifier borate glasses. These bands have been assigned to the stretching of B-O - stretching in metaborate rings and chains.