Upconversion luminescence in bismuth-germanate oxide glasses co-doped with lanthanide ions

In this article, bismuth-germanate oxide glasses doped and co-doped with rare earth ions have been synthesized. Fabricated glass is characterized by good thermal stability (ΔT = 127°C) which are necessary for further forming them into photonic waveguides and low phonon-energy (ħω = 724 cm^-1), much important in upconversion processes. Besides, presented glasses have a low absorption coefficient (<0.5 cm^-1) in examined visible wavelength range. Upconversion luminescence spectra under 980 nm laser diode excitation have been observed in glasses doped with Er³⁺ and co-doped with Er³⁺/Eu³⁺, Er³⁺/Ho³⁺, Er³⁺/Pr³⁺ and Er³⁺/Nd³⁺ ions. According to emission parameters analysis, higher luminescence intensity in co-doped samples resulting from energy transfer phenomenon between active ions was observed. This demonstrates that bismuth-germanate oxide glass co-doped with proper rare earth elements system is an attractive material for applications working in visible range.