Energy transfer and upconversion processes in Nd^3+-doped GeO_2–PbO–Nb_2O_5 glass

The optical properties of Nd3+-doped lead germanate glass of composition (in mol. %) 60GeO2–25PbO–15Nb2O5 have been investigated for several Nd3+ concentrations at various temperatures by steady-state and time-resolved laser spectroscopy. Judd–Ofelt parameters were derived from the absorption spectrum and used to calculate the 4F3/2→4I11/2 stimulated-emission cross section and the 4F3/2 radiative lifetime. The spectral features of the time-resolved fluorescence line narrowing 4F3/2→4I9/2 emission spectra obtained under resonant excitation reveal the existence of spectral migration of excitation among the Nd3+ ions. Analysis of the time evolution of the 4F3/2→4I9/2 narrowed emission showed that the electronic mechanism responsible for the ion–ion interaction can be identified as a dipole–dipole energy-transfer process. Green, orange, and red emissions were observed in this glass under continuous-wave infrared laser excitation and are attributed to transitions from the 4G7/2 level.