Upconversion from fluorophosphate glasses prepared with NaYF₄:Er³⁺,Yb³⁺ nanocrystals

The direct doping method was applied to fabricate upconverter fluorophosphate glasses in the system (90NaPO₃-(10-x)Na₂O-xNaF) (mol%) by adding NaYF₄:Er³⁺,Yb³⁺ nanocrystals. An increase in the network connectivity, a red shift of the optical band gap and a decrease in the thermal properties occur when Na₂O is progressively replaced by NaF. To ensure the survival and the dispersion of the nanocrystals in the glasses with x = 0 and 10, three doping temperatures (T _doping) (525, 550 and 575 °C) at which the nanocrystals were added in the glass melt after melting and 2 dwell times (3 and 5 minutes) before quenching the glasses were tested. Using 5 wt% of the NaYF₄:Er³⁺,Yb³⁺ nanocrystals, green emission from the NaYF₄:Er³⁺,Yb³⁺ nanocrystals-containing glasses was observed using a 980 nm pumping, the intensity of which depends on the glass composition and on the direct doping parameters (T _doping and dwell time). The strongest upconversion was obtained from the glass with x = 10 prepared using a T _doping of 550 °C and a 3 min dwell time. Finally, we showed that the upconversion, the emission at 1.5 μm and of the transmittance spectra of the nanocrystals-containing glasses could be measured to verify if decomposition of the nanocrystals occurred in glass melts during the preparation of the glasses.