Evaluation of spectral parameters of Nd3+ ion in borate glasses. Part 2. Judd-Ofelt parameters

Optical absorption spectra of Nd3+ doped alkali borate glasses have been an alysed using the Judd-Ofelt (J-O) theory of crystal field induced electric dipole transitions. Analysis yielded some of the important spectroscopic pa rameters, namely radiative transition probabilities, radiative lifetimes, f luorescence branching ratios and optical gain of the principal fluorescence transitions originating from the F-4(3/2) metastable level. Variations of these parameters with glass compositions and their implications for tailori ng spectroscopic properties by compositional changes are discussed. To unde rstand the laser efficiency of the material, the value of the spectroscopic quality factor (Q) is measured as a function of the fluorescence branching ratio and the quantum efficiency of the F-4(3/2)-->I-4(11/2) emission comp onent is obtained from the measured and calculated lifetimes. Also the stim ulated emission cross section corresponding to this transition is obtained from the respective emission lineshapes. Values of stimulated emission cros s section are comparable with those of other glassy hosts used in solid sta te laser applications The quantum efficiency of the F-4(3/2)-->I-4(11/2) tr ansition is found to be low in comparison with other glassy matrices and is attributed to high nonradiative multiphonon relaxation rates in the borate matrix. In addition to this the intensity parameters are used to evaluate the linestrengths for excited state absorption from the metastable F-4(3/2) manifold. Significant linestrengths are predicted at wavelengths near 1.04 4 and 1.326 mu m suggesting the possibility of radiative depumping of the F -4(3/2) upper laser level via the stimulated emission field.