Energy transfer and frequency upconversion in Er3+-Yb3+ codoped oxy-fluoro-tungstosilicate glasses

Er3+-Yb3+ codoped oxy-fluoro-tungstosilicate glasses with infrared-to-visible frequency upconversion luminescence were prepared by melting quenching in air. The effects of Er3+ doping on the optical properties of the samples were measured by means of techniques such as optical absorption spectra and photoluminescence spectra. The results showed that intense green and red signals centered at 546 and 665 nm, corresponding to the 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ by a multiphoton stepwise phonon-assisted excited-state absorption process, respectively, were simultaneously observed by exciting the samples with a diode laser operating at 980 nm at room temperature. The upconversion process was found very sensitive to Er3+ content at a constant Yb2O3 content of 5 mol.%. With the increase of Er3+ content from 0.5% to 1.5%, the upconversion intensity increased gradually. Further increasing of Er3+ content to 3.0% resulted in a significant fluorescence quenching. Moreover, the possible upconversion mechanisms were discussed based on the energy-matching conditions and the quadratic dependence on excitation power.