Effects of Er3+ concentration on upconversion luminescence and temperature sensing properties in Bi4Ge3O12 crystal

Er3+ doped Bi4Ge3O12(BGO) crystals with different Er3+ ion concentration were prepared by Bridgman-Stockbarge (B–S) method and the temperature dependence of its upconversion (UC) luminescence was investigated systematically. The phases and luminescence properties of all the samples were characterized by X-ray diffraction (XRD) and upconversion luminescence (UCL) spectra. The temperature sensing performance of Er3+ doped Bi4Ge3O12 sample was studied via the fluorescence intensity ratio method from two thermally coupled 2H11/2 and 4S3/2 levels. Excited by 980 nm laser, the sensitivity first increased and then decreased with the increase of Er3+ ion concentration, and the maximum sensitivity can be obtained in the 0.3 mol% Er3+ doped sample at 498 K for 50.3 × 10−4 K−1. Meanwhile, the experiment also proved that Er3+ doped BGO as temperature sensing has a high reliability and repeatability. The influence mechanism of concentration on temperature sensing was studied by using the calculation of the Judd-Ofelt (J-O) theory, 0.3 mol% Er3+ doped Bi4Ge3O12 sample had a larger the ratio of the green radiation transition rate at the thermal coupling level. These results indicated that Er3+ doped Bi4Ge3O12(BGO) crystals may be a good candidate material as optical temperature sensor.