Study of the spectroscopic properties and infrared-to-visible up-conversion fluorescence of Er3+-doped germanate glasses

Raman scattering, optical absorption and photoluminescence studies have been performed on Er3+-doped Na2O-Nb2O5-GeO2 germanate-based glasses. The main bands in the Raman spectra involve vibrational modes associated with the germanium oxide network. Judd-Ofelt intensity parameters were determined and then used to calculate the radiative transition rates and excited-state radiative lifetimes. Green and red up-conversion luminescence was observed at room temperature under 800 nm laser line excitation. The emission intensities have a quadratic dependence on the excitation pump power, indicating a two-step upconversion mechanism. The intensity of the 660 nm red band shows an increase relative to the 554 nm green band with increasing Er3+ content. Combined with the time-resolved luminescence data of the emitting states, we suggest from these results that the up-conversion process is attributed to a competitive situation of excited-state absorption and energy transfer between excited ions accompanied by multiphonon relaxation. (C) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.