Photoluminescence and mixed-valence tuning of Eu in Sr2(Al,Ga)2SiO7 phosphors for sensitive thermometric applications

The regulation on chemical components is a valid way to develop rare earth doped phosphors of well-luminescent performances. In this work, the photoluminescence and mixed valences of Eu2+/3+ in Sr2(Al, Ga)2SiO7 can be tuned by Ga3+ regulation. The site-dependent luminescence of Eu2+ in Sr2(Al, Ga)2SiO7 are discussed on the basis of VUV-UV–vis spectra. With the gradual replacement of Ga3+ ions, both the ratio of Eu3+ contents and the proportion of Eu3+ emission increase with respect to that of Eu2+. Ab initio calculation and simulation of X-ray photoelectron spectra (XPS) are adopted to get deep insight. It was found that the increase ratio of Eu3+ to Eu2+ is mainly due to the decrease of band gap and fermi level. As results, emission color of Sr2(Al, Ga)2SiO7: Eu2+/3+ is tunable with different replaced Ga3+ contents, wavelengths and temperatures. Series of temperature-dependent measurements indicate that the Eu2+/ Eu3+ ratiometric emission can sensitively denote the variation of temperature under excitation at 300 nm. After the fine-modification by Ga3+, Sr1.9Eu0.1Al1.9Ga0.1SiO7 phosphor shows sensitive temperature readout.