Laser spectroscopy of Nd3+ ions in GeO2-PbO-Bi2O3 glasses

The optical properties of Nd3+ ions in six different compositions of glasses based on GeO2, PbO, and Bi2O3 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 F-4(3/2)-->I-4(11/2) Stimulated emission cross section and the F-4(3/2), radiative lifetime. Site-selective spectroscopy and time resolved fluorescence line narrowing experiments were performed in the F-4(3/2)-->I-4(9/2), I-4(11/2) transitions. For all samples studied a line narrowing of the F-4(3/2)-->I-4(1/2) emission has been observed when exciting at the long wave side of the I-4(9/2)-->F-4(3/2) transition. The lifetimes of the F-4(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 Nd3+ ions has been studied from the time evolution of the F-4(3/2)-->I-4(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.