Photoluminescence of partially reduced Eu2+/Eu3+ active centers in a NaF–Al2O3–P2O5 glassy matrix with tunable smooth spectra

摘要： In this work, a series of photoluminescent materials have been synthesized based on optically transparent and chemically stable glasses of the nominal composition Na3Al2(PO4)2F3 (NaF–Al2O3–P2O5 system) doped with 1 wt % of europium. It has been shown that the synthesis conditions (mainly the temperature and duration of the melting stage under reducing conditions) strongly affected the photoluminescence spectra of the material. This effect has been ascribed to varying proportions between Eu3+ and Eu2+ ions concentrations, imposed by the synthesis conditions, which was confirmed by XPS, absorption and decay times measurements. As both Eu3+ and Eu2+ centers exhibit photoluminescence in different ranges of the visible spectra (Eu3+ – red, and Eu2+ – mainly blue) the possibility, shown by us, to control relative proportions of the oxidation states of europium and consequently to control the photoluminescence spectra, may be advantageous from the viewpoint of potential applications of such materials as novel phosphors for white LEDs with the emission spectra resembling natural light.