C.K. Jayasankar

Optical properties of Sm3+ ions in lithium borate and lithium fluoroborate glasses

Optical absorption, excitation, emission spectra and lifetimes are presented for Sm3+ ions in lithium borate and lithium fluoroborate glasses. Compositional dependence of Judd–Ofelt parameters has been evaluated and these parameters are used to predict radiative lifetimes (τR) and branching ratios (βR) for some excited 4G(4)7/2, 4G(4)5/2, 6F11/2, 6F9/2, 6F1/2, 6H13/2, 6H11/2 and 6H9/2 levels. The radiative properties have also been predicted for these excited levels of Sm3+:borate, oxide, phosphate, fluoride and fluorophosphate glasses and Sm3+:Y3Al5O12 crystal. The values of electric (Aed) and magnetic (Amd) dipole transition probabilities, τR and βRare presented for the above excited levels. The Judd–Ofelt intensity parameters have been used to predict oscillator strengths which are found to be useful to assign the closely spaced multiplets. The predicted values of τR and βR are compared with the experimental values for 4G(4)5/2 level to its lower levels. The stimulated emission cross-sections, σ(λp), were also evaluated for 4G(4)5/2→6HJ transitions. The dependence of the optical properties due to compositional changes of the glasses are discussed and compared with similar results.

Spectroscopic properties of Dy3+ ions in lithium borate and lithium fluoroborate glasses

Abstract Spectral study of Dy3+-doped borate glasses modified with lithium oxide and fluoride are presented. These glasses include lithium borates: (99−x)Li2CO3+xH3BO3+1Dy2O3,x=39.5, 49.5, 59.5 and 69.5 and lithium fluoroborates: xLi2CO3+(49.5−x)LiF+49.5H3BO3+1Dy2O3,x=24.75 and 0. Using Judd–Ofelt (JO) theory, the intensity parameters ( Ω λ , λ=2,4,6 ) have been evaluated for all the six glasses. These intensity parameters are used to predict radiative properties that include electric (Sed) and magnetic (Smd) dipole line strengths, radiative (A) and total radiative (AT) transition probabilities, lifetimes (τR), branching ratios (βR) for the excited ( 4 K (1) 13/2 , 4 F (3) 5/2 , 4 P (2) 3/2 , 4 M 21/2 , 4 G (4) 11/2 , 4 I (3) 15/2 , 4 F (3) 9/2 , 6 F 9/2 and 6 H 9/2 ) levels of these Dy3+-doped lithium borate and lithium fluoroborate glasses along with 11 different systems doped with Dy3+ ions. The predicted values of τR and βR are compared with the experimental values for 4 F (3) 9/2 transition. The stimulated emission cross-sections are also evaluated for 4 F (3) 9/2 → 6 H J (J=7/2,9/2,11/2,13/2 and 15/2) transitions. The dependence of the spectral characteristics of Dy3+ ions due to compositional changes of the glasses are examined.

On the local structure of Eu3+ ions in oxyfluoride glasses. Comparison with fluoride and oxide glasses

Broadband and fluorescence line narrowing optical spectroscopic studies have been used to investigate the local environments of Eu3+ ions in lithium fluoroborate glasses. From the vibronic spectra, different borate groups coupled with the Eu3+ ions have been identified. A pulsed tunable dye laser has been used to selectively excite the 5D0 level of the Eu3+ ion and the subsequent 5D0→7F1 fluorescence spectra have been monitored as a function of the exciting wavelength. From these FLN studies, three 7F1 Stark levels have been identified and a C2v orthorhombic symmetry has been assumed in the subsequent calculation of the crystal-field parameters for the different environments occupied by the Eu3+ ions in the glass. The second rank crystal-field parameters have been systematically analyzed for the Eu3+:lithium fluoroborate glass from the site dependent behavior of the 7F1 level splitting. The importance of the J-mixing in the crystal-field analysis has been emphasized. An appropriate method for comparing th...

Optical spectroscopy, 1.5μm emission, and upconversion properties of Er 3+ -doped metaphosphate laser glasses

Metaphosphate glasses doped with five concentrations of Er3+ ions have been investigated through absorption and emission spectra, decay curves, and upconversion measurements. Judd-Ofelt parameters have been evaluated from absorption spectrum of the 1.0mol.%Er3+-doped glass, which are in turn used to predict radiative properties of some important luminescence levels of Er3+ ions in these glasses. Gain bandwidths of an optical amplifier have been evaluated and are compared with those of reported Er3+:glass systems. Temperature dependence of the 1.5μm emission has been studied for the 2.0mol.%Er3+-doped glass from 13K to room temperature. Lifetimes of the I13/24 level were measured and are found to decrease with concentration of Er3+ ions after 0.1mol.%. Concentration quenching of lifetimes has been analyzed using the theory developed by Auzel [J. Lumin.94-95, 293 (2001); Opt. Mater.24, 103 (2003)]. Infrared to visible upconversion was also measured for three concentrations of Er3+-doped metaphosphate glasses with 794nm excitation. A mechanism, involving excited state absorption and energy transfer upconversion, has been proposed to explain the upconversion process.

White light generation in Dy 3+ -doped oxyfluoride glass and transparent glass-ceramics containing CaF 2 nanocrystals

The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram.

Dy3+-doped zinc fluorophosphate glasses for white luminescence applications

Dysprosium (Dy(3+)) ions doped zinc fluorophosphate (PKAZLFDy: P2O5-K2O-Al2O3-ZnF2-LiF-Dy2O3) glasses have been prepared and investigated their spectroscopic properties using absorption, emission and decay measurements. Judd-Ofelt analysis has been carried out to obtain the intensity parameters and in turn predicted radiative properties for the (4)F9/2 level of 1.0 mol% of Dy2O3 doped glass. Visible luminescence spectra have been obtained due to (4)F9/2→(6)HJ (J=11/2, 13/2, 15/2) transitions of Dy(3+) ions under 385 nm excitation. The yellow-to-blue luminescence intensity ratios and chromaticity coordinates of Dy(3+) ions in these glasses have been analyzed as a function of Dy(3+) ion concentration. The decay profiles for the (4)F9/2 level exhibit perfectly single exponential at lower concentrations (up to 1.0 mol%) and turn into non-exponential for higher concentrations (>1.0 mol%) due to energy transfer between donor (excited state Dy(3+) ion) and acceptor (ground state Dy(3+) ion). The results reveal that these glasses emit bright white light which is suitable for the development of W-LEDs.

Spectral investigations on Dy3+-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the F49/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 μm, useful for optical amplification in fiber amplifiers.

Optical properties of Er3+ ions in lithium borate glasses and comparative energy level analyses of Er3+ ions in various glasses

Abstract The electronic structure of Er 3+ ions are studied in the following lithium borate (LBO) glasses: Li 2 CO 3 + H 3 BO 3 and RCO 3 + Li 2 CO 3 + H 3 BO 3 (R = Mg, Ca, Sr and Ba). The electronic structure of Er 3+ (4f 11 ) in these glasses as well as the data that are available for other systems in the literature are also analyzed in terms of a Hamiltonian model that consists of 20 interaction parameters of atomic nature. The energy level analyses resulted in good correlation between the calculated and experimentally observed energies. The matrix elements for the transitions of Er 3+ :LBO glasses are calculated in the intermediate coupling scheme using the measured energies in these glasses. Using the Judd-Ofelt theory, the intensity parameters are obtained from these matrix elements and experimentally obtained oscillator strengths. Radiative properties for fluorescent levels of Er 3+ ions in LBO glasses are evaluated. The similarities and differences in the radiative characteristics of Er 3− :LBO glasses and other Er 3+ :glasses are discussed.

Correlation-crystal-field analysis of Nd3+(4f3) energy-level structures in various crystal hosts

We have performed an in-depth correlation-crystal-field (CCF) analysis of the energy-level structures in 10 Nd3+(4f3) crystal systems: NdF3, Nd2Te4O11, NdVO4, NdPO4, Nd3+:LiYF4, Nd3+:LaVO4, Nd3+:LaCl3, Nd3+:BaY2F8, Nd3+:YAlO3 and Nd3+:LuA1O3. A model Hamiltonian employing 20 free-ion parameters, appropriate one-electron crystal-field interaction parameters and also selected two-particle CCF interaction parameters was diagonalized within the complete 364 SLJMJ basis set of the 4f3 electronic configuration. Inclusion of the fourth-rank g2(4), g10A(4) and g10B(4) CCF operators in the phenomenological energy-level fits yields an overall improved agreement between calculated and empirical energy levels besides eliminating major discrepancies between calculated and observed crystal-field splittings within the anomalous 2H(2)11/2 multiplet of Nd3+ ion. The fits are also in qualitative agreement with the ab initio calculations of CCF effects for lanthanide ions.

Thermal, structural and optical properties of Eu3+-doped zinc-tellurite glasses

Europium doped zinc-tellurite glasses modified with LiF, Na2 O+L i 2O and Na2 O+L i2 O+N b 2O5 were prepared by the conventional melting procedure and their thermal, structural and optical properties were investigated. Differential thermal analysis curves in the temperature range 30–1200 ◦ Ca t a heating rate of 10 ◦ C min −1 were used to determine the thermal properties such as glass transition, crystallization and melting temperature. FT-IR spectra were used to analyse the glass structure. The spectroscopic properties including absorption and emission spectra and fluorescence lifetime of Eu 3+ ions were measured. A strong red fluorescence is observed from the 5 D0 level of Eu 3+ ions in these glasses. The relative luminescence intensity ratio (R )o f 5 D0→ 7 F2 to 5 D0→ 7 F1 transitions has been evaluated to estimate the local site symmetry around the Eu 3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5 D0→ 7 F1 transition of Eu 3+ ions. Based on the energy level data obtained from the absorption and emission measurements, free-ion energy level analysis has been carried out. Second rank crystal-field parameters have been calculated together with the crystal-field strength parameter by assuming the C2v symmetry for the Eu 3+ ions in these glasses. The crystal-field parameters are found to be higher in binary zinc-tellurite glasses. The trend of variation of crystal-field strength with glass composition is found to be more or less opposite to that of R in the present glasses. The effect of temperature on the luminescence from 5 D1 level is studied. The decay from the 5 D0 level is found to be exponential and the lifetime is shorter than those found in Eu 3+ -doped borate, phosphate and fluoride based glasses.