Simultaneous modulation of multicolor upconversion emission and thermal‐sensing performance of Ba₅Zn₄Y₈O₂₁ phosphors

In this study, we report the modulation of the emission color and optical temperature‐sensing properties of Er 3+ in Ba 5 Zn 4 Y 8 O 21 crystals. Er 3+ single‐doped Ba 5 Zn 4 Y 8 O 21 phosphors showed green emission under 980 nm excitation. When codoping with Yb 3+ ions, the red emission component from the Er 3+ ions increased significantly, and the sample emission turned orange. Yb 3+ –Er 3+ codoped Ba 5 Zn 4 Y 8 O 21 samples exhibited bright red emission with a maximum I R / I G value of 89.30 when excited with a longer wavelength, 1550 nm. A broad range of emission colors could be modulated by adjusting the dopant concentration. The possible modulation mechanisms and upconversion processes were analyzed based on the luminescence decay curves and power‐dependent emission intensities. Furthermore, the optical temperature‐sensing properties of Ba 5 Zn 4 Y 8 O 21 :Er 3+ and Ba 5 Zn 4 Y 8 O 21 :Er 3+ , Yb 3+ phosphors with thermal coupled energy levels (TCELs) and nonthermal coupled energy levels (N‐TCELs) of Er 3+ ions were investigated using fluorescence intensity ratio technique. Based on the TCELs ( 2 H 11/2 / 4 S 3/2 ), the Er 3+ single‐doped and Yb 3+ –Er 3+ codoped Ba 5 Zn 4 Y 8 O 21 phosphors present the similar optical thermometry behaviors under 980 and 1550 nm excitation. The highest absolute ( S a ) and relative sensitivity ( S r ) are 3.95 × 10 −3 K −1 at 573 K and 1.31% K −1 at 303 K, respectively. Based on N‐TCELs ( 4 F 9/2 / 2 H 11/2 ), the temperature‐sensing performance depends on the Yb 3+ dopant and excitation wavelength. The highest values for S a and S r reached 5.46 K −1 at 303 K and 1.38% K −1 at 573 K for the Ba 5 Zn 4 Y 8 O 21 :Er 3+ , Yb 3+ phosphor under 1550 nm excitation, respectively. In addition, the present phosphor exhibited high stability and repeatability over a wide temperature range. These results indicate that the multicolor modulation upconversion Ba 5 Zn 4 Y 8 O 21 ‐based phosphor can be considered a potential reusable optical thermometer for noncontact temperature detection.