Upconversion luminescence color modulation and temperature sensing of Na0.5Bi2.5Nb2−xTaxO9:Er3+/Yb3+ phosphors.

A series of Na0.5Bi2.5Nb2−xTaxO9 (NBN2−xTx):Er3+/Yb3+ 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 Er3+/Yb3+ is 0.14 and 0.26 by replacing Bi3+ sites in NBN2−xTx host, respectively. With the increase of Ta5+ 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 Er3+ to Er3+ and energy back transfer from Er3+ to Yb3+. Using the luminescence intensity ratio technique, the maximum absolute sensitivities (SA) are obtained as 0.00674 K−1 at 538 K and 0.00603 K−1 at 573 K, and relative sensitivities (SR) are obtained as 0.01174 K−1 at 303 K and 0.01244 K−1 at 303 K based on 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 energy level transitions of Er3+ in NBN2:0.14Er3+/0.26Yb3+ phosphors under 980‐ and 1550‐nm laser excitations, respectively. The results suggest that the NBN2−xTx:Er3+/Yb3+ phosphors are promising candidates for temperature sensing with different UL colors. [ABSTRACT FROM AUTHOR]