Line-narrowed fluorescence spectra and site-dependent transition probabilities ofNd3+in oxide and fluoride glasses

Abstract

The fluorescence spectra, branching ratios, and decay of the $^{4}F_{\frac{3}{2}}$ state of ${\mathrm{Nd}}^{3+}$ in glass were measured under excitation by tunable pulsed laser radiation. The following glass types were studied: silicate, phosphate, borate, fluoroberyllate, and fluorophosphate. Measurements were made at liquid-helium temperatures by exciting into the $^{2}P_{\frac{1}{2}}$ state, and line-narrowed fluorescence spectra were obtained as a function of excitation wavelength. Large variations in Stark splitting of the $^{4}I_{\frac{9}{2}}$ and $^{4}I_{\frac{11}{2}}$ states have been observed and attributed to site-to-site differences in the local crystal field. The probabilities for radiative decay and for nonradiative decay by multiphonon emission also exhibit variations with excitation wavelength. Although similarities exist, each different glass type shows its own distinctive patterns of variation in crystal-field splitting and relative quantum efficiency. In the fluorophosphate glass, which contains large numbers of both fluorine and oxygen anions, comparison of the laser-excited fluorescence spectra and lifetime of ${\mathrm{Nd}}^{3+}$ with the corresponding results from pure oxide and fluoride glasses demonstrates the presence of ${\mathrm{Nd}}^{3+}$ sites having both fluorine and oxygen nearest-neighbor coordination.