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

Abstract 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 up‐conversion 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. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)