Fluorine losses in Er3+ oxyfluoride phosphate glasses and glass-ceramics

Er3+ doped phosphate glasses with the composition 75NaPO(3-)25CaF(2) (mol%) were prepared at different melting temperatures to demonstrate the importance to quantify the fluorine content when preparing oxyfluoride glasses. Indeed, increasing the melting temperature from 900 to 1000 degrees C leads to a small reduction in the fluorine content from 9.4 at % to 8.8 at % as quantified using EPMA. Whereas this loss of fluorine can be suspected from small changes in the thermal properties of the glass, it increases significantly the glass crystallization tendency in this glass system. This means that a heat treatment of the as-prepared glass should be performed when evaporation of fluorine during the glass melting is suspected. Sample preparation for the characterization of the spectroscopic properties of the glasses is discussed here as well; bulk glasses should be used when measuring the spectroscopic properties of oxyfluoride glasses, which are known to be hygroscopic. It is shown, in this work, that a heat treatment of the glass within the investigated glass system leads to transparent glass-ceramics with volume precipitation of Er3+ doped CaF2 crystals with strong upconversion. (C) 2019 Elsevier B.V. All rights reserved.