Composition and concentration dependence of spectroscopic properties of Nd 3+-doped tellurite and metaborate glasses

• Published in: Optical materials 2011-04, Vol.33 (6), p.928-936
• Main Authors: Jyothi, L., Venkatramu, V., Babu, P., Jayasankar, C.K., Bettinelli, M., Mariotto, G., Speghini, A.
• Format: Article
• Language: English
• Subjects: Concentration (composition); Decay; Emission analysis; Energy transfer; Germanates; Glass; Judd–Ofelt analysis; Lithium; Metaborate glasses; Neodymium; Optical properties; Phosphates; Spectroscopy; Tellurite glasses
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2010.11.015

► The optical properties of different concentrations of Nd 3+-doped tellurite (modified with Nb 2O 5/K 2O/Li 2O) and 1.0 mol% Nd 3+-doped borate (modified with Nb 2O 5) glasses have been investigated. ► The higher value of the Ω 2 parameter for 1.0 mol% Nd 3+-doped tellurite glass indicates its stronger Nd 3+-ligand covalent bond and/or higher asymmetry around Nd 3+ ions. ► The 1.0 mol% Nd 3+-doped tellurite glass possess a smaller spectroscopic quality factor which indicates that the 4F 3/2 → 4I 11/2 laser transition is relatively stronger in this glass than the 1.0 mol% Nd 3+-doped borate glass. ► In the present tellurite glasses, the cross-relaxation energy transfer between Nd 3+ ions is of dipole–dipole nature and the energy transfer through diffusion also plays a prominent role, both the energy transfer processes increase with increase in Nd 3+ ions concentration. The spectroscopic properties of tellurite glasses of composition (in mol%) TNKNd: (70 − x)TeO 2–15Nb 2O 5–15K 2O– xNd 2O 3 ( x = 0.1, 1.0, 1.5, 2.0 and 2.5) and TNLNd10: 69TeO 2–15Nb 2O 5–15Li 2O–1.0Nd 2O 3 and lithium metaborate glass of composition LBNNd10: 89LiBO 2–10Nb 2O 5–1.0Nd 2O 3 have been investigated using absorption and emission spectra and decay curve analysis. An energy level analysis has been carried out considering the experimental energy positions of the absorption and emission bands, using the free-ion Hamiltonian model. The spectral intensities have been calculated by using the Judd–Ofelt theory and in turn the radiative properties such as radiative transition probabilities, emission cross-sections, branching ratios and radiative lifetimes have been estimated. The decay curves at the lower concentrations are exponential while they show a non-exponential behavior at higher concentrations (⩾1.0 mol%) due to energy transfer processes. The effective lifetimes for the 4F 3/2 level are found to decrease with increase in Nd 2O 3 concentration for all the glasses under investigation. The non-exponential decay curves have been well-fitted to the Yokota–Tanimoto model with S = 6, indicating that the nature of energy transfer is of dipole–dipole type and energy migration also plays an important role. The results obtained have been compared with Nd 3+-doped phosphate, fluorophosphate, lead borate, tellurite, germanate and silicate glasses and Nd 3+-doped YAG ceramic and Ca 2Nb 2O 7 crystals.