Ultra-broadband cyan-to-orange emitting Ba1+xSr1−xGa4O8:Bi3+ phosphors: luminescence control and optical temperature sensing

Abstract

Herein, we report a new series of Ba_1+xSr_1−xGa₄O₈:Bi³⁺ (x = 0–0.7) phosphors that exhibit extremely broadband emission, covering almost the entire visible region and extending to the deep-red region, when excited by ultraviolet light. BaSrGa₄O₈:Bi³⁺ exhibits two emission bands located at 470 and 570 nm originating from different emission centers. With the gradual substitution of Ba for Sr, both of the emission bands show a red-shift, from 470 to 510 nm and from 570 to 630 nm, respectively. The corresponding full width at half maximum (FWHM) increases from 192 to 283 nm, which is attributed to a superposition of multiple emission centers via crystal field regulation. As a result, the emission can be tuned from cyan to orange across the warm white light region in Ba_1+xSr_1−xGa₄O₈:Bi³⁺ (x = 0–0.7) systems. Simultaneously, this series of phosphors presents good thermal stability (97% intensity at 150 °C for the Ba_1.5Sr_0.5Ga₄O₈:Bi³⁺ sample) and the thermal quenching will decrease with the formation of a solid solution due to the increasing rigidity of the lattice structure. Interestingly, the two emission bands in the representative Ba_1+xSr_1−xGa₄O₈:Bi³⁺ (x = 0–0.7) sample exhibit different thermal responses to increasing temperature, thus an optical thermometer with color discrimination and good sensitivity is designed. The maximum relative sensitivity (S_r) is 1.295% K⁻¹ in the temperature range of 7–400 K. The corresponding emission color can be tuned from blue-cyan to orange, including white light. This work presents a rational design strategy for controllable ultra-broadband emission tuning across the white light region and to further explore potential optical sensor applications.