Effects of Yb3+ concentration on up-conversion luminescence and temperature sensing characteristics of Tm3+/Yb3+:Y2O3 phosphors

Y2O3:0.5 mol%Tm3+/x mol%Yb3+(x = 3, 5, 7, 10) luminescent materials have been synthesized by the CO2 laser zone melting method. With 980 nm excitation, the up-conversion luminescence (UCL) emission bands corresponding to 1G4→3H6, 1G4→3F4, 3F2,3→3H6, and 3H4→3H6 transitions of Tm3+ ions were obtained in visible and near-infrared spectral regions, among which the luminescence emitted by 1G4→3H6, 3H4→3H6 transitions shows obvious Stark splitting. Besides, the optimal doping concentration of Yb3+ is 5 mol%. The up-conversion luminescence spectra of Y2O3:0.5 mol%Tm3+/5 mol%Yb3+ were recorded from 224 K to 873 K. The temperature sensing properties of 3F2,3 and 3H4, 1G4(a) and 1G4(b) energy levels of Tm3+ ions were investigated by the luminescence intensity ratio (LIR) method in a wide temperature range, and the possibility of using 3H4(a), 3H4(b) thermally coupled levels (TCLs) of Tm3+ ions for temperature sensing was developed. The results show that 1G4(a) and 1G4(b), 3F2,3 and 3H4, 3H4(a) and 3H4(b) of Tm3+ ions are TCLs, and the Stark sub-levels own relatively high absolute sensitivity at low temperature, whereas the 3F2,3 and 3H4 TCLs of Tm3+ ions are more suitable for high temperature measurement. The results show that the Tm3+/Yb3+:Y2O3 luminescent material can be a promising candidate for temperature sensing.