Upconversion luminescence of Ba3La(PO4)3:Yb3+-Er3+/Tm3+ phosphors for optimal temperature sensing.

Abstract

To explore new upconversion (UC) luminescent materials for optical temperature sensing, a series of Ba3La1-x(PO4)3:0.1Yb3+,xEr3+ (abbreviated as BLP:0.1Yb3+, xEr3+, 0.01≤x≤0.03) and Ba3La1-y(PO4)3:0.1Yb3+,yTm3+ (abbreviated as BLP:0.1Yb3+, yTm3+, 0.005≤y≤0.015) phosphors was designed. For Yb3+-Er3+ codoped BLP, the UC emission spectra exhibit a gradual enhancement with increasing pump power, and two-photon process for the green and red emissions of Er3+ has been confirmed by studying the dependence of UC emission intensities on excitation power. When the temperature rises, the fluorescence intensity ratio (FIR) for the H11/22-4I15/2 and S3/24-4I15/2 emissions of Er3+ increases gradually due to the thermalization of populations at the H11/22 and S3/24 levels. With the temperature increased, the absolute sensitivity (SA) shows a continuous increase and reaches about 4.38×10-3 K-1 at 498K, but the relative sensitivity (SR) decreases gradually. For Yb3+-Tm3+ codoped BLP, the emission intensity of Tm3+ shows a gradual decrease with increasing Tm3+ concentration. By studying the temperature dependence of FIR for the (F23,F33)-H63 and H43-3H6 emissions, it has been found the sample exhibits a higher SR value but a lower SA value relative to the Yb3+-Er3+ codoped BLP.