Upconversion luminescence color modulation and temperature sensing of Na <sub>0.5</sub> Bi <sub>2.5</sub> Nb <sub>2−</sub> <i> <sub>x</sub> </i> Ta <i> <sub>x</sub> </i> O <sub>9</sub> :Er <sup>3+</sup> /Yb <sup>3+</sup> phosphors
Lei Li, Yongze Cao, Hongqiang Cui, Yuhang Zhang, Guojian Li, Yichao Wang, Xiangping Li, Sai Xu, Baojiu Chen
Abstract
Abstract A series of Na 0.5 Bi 2.5 Nb 2− x Ta x O 9 (NBN 2− x T x ):Er 3+ /Yb 3+ upconversion luminescence (UL) phosphors were prepared by a solid‐state sintering method, and the lattice structure of the prepared samples was studied by X‐ray diffraction. Under 980‐nm laser excitation, the UL properties were investigated by a spectrophotometer from room temperature to 723 K, and the optimal concentration of co‐doping Er 3+ /Yb 3+ is 0.14 and 0.26 by replacing Bi 3+ sites in NBN 2− x T x host, respectively. With the increase of Ta 5+ concentration, the color of UL gradually changes from green to yellow corresponding color coordinates from (0.301, 0.682) to (0.441, 0.549) under 980‐nm laser excitation. This color change is attributed to the decrease of lattice unit volume leading to the increase of cross relaxation of Er 3+ to Er 3+ and energy back transfer from Er 3+ to Yb 3+ . Using the luminescence intensity ratio technique, the maximum absolute sensitivities ( S A ) are obtained as 0.00674 K −1 at 538 K and 0.00603 K −1 at 573 K, and relative sensitivities ( S R ) are obtained as 0.01174 K −1 at 303 K and 0.01244 K −1 at 303 K based on 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 energy level transitions of Er 3+ in NBN 2 :0.14Er 3+ /0.26Yb 3+ phosphors under 980‐ and 1550‐nm laser excitations, respectively. The results suggest that the NBN 2− x T x :Er 3+ /Yb 3+ phosphors are promising candidates for temperature sensing with different UL colors.