Laser spectroscopy of ${\mathrm{Nd}}^{3+}$ ions in ${\mathrm{GeO}}_2{-\mathrm{P}\mathrm{b}\mathrm{O}-\mathrm{B}\mathrm{i}}_2{\mathrm{O}}_3$ glasses

The optical properties of ${\mathrm{Nd}}^{3+}$ ions in six different compositions of glasses based on ${\mathrm{GeO}}_2,$ PbO, and ${\mathrm{Bi}}_2{\mathrm{O}}_3$ have been investigated by using steady-state and time-resolved laser spectroscopy. Judd-Ofelt parameters were derived from the absorption spectra and used to calculate the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{11/2}$ stimulated emission cross section and the ${}^4{F}_{3/2}$ radiative lifetime. Site-selective spectroscopy and time resolved fluorescence line narrowing experiments were performed in the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{9/2}{,}^4{I}_{11/2}$ transitions. For all samples studied a line narrowing of the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{11/2}$ emission has been observed when exciting at the long wave side of the ${}^4{\overrightarrow{I_{9/2}}}^4{F}_{3/2}$ transition. The lifetimes of the ${}^4{F}_{3/2}$ state do not show a monotonic variation with the excitation wavelength indicating large site-to-site variations in the local crystal field. Spectral migration of excitation among the ${\mathrm{Nd}}^{3+}$ ions has been studied from the time evolution of the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{9/2}$ spectra under resonant excitation. The results can be interpreted in terms of a dipole-dipole energy transfer mechanism. Visible upconversion has been observed in these glasses under infrared laser excitation.