Dual-modal optical thermometry based on near-infrared emission of Cr3+ with high relative sensitivities over a wide temperature range

Broad band near-infrared (NIR) emitting phosphors activated with Cr 3+ ions hold great potential for diverse applications. Microcrystalline barium gallate powders activated with Cr 3+ were synthesized, and their phase structure, photoluminescence properties as well as their potential uses in luminescence thermometry and plant cultivation, are investigated. It is revealed that Ba 1.3 Ga 12 O 19.3 : Cr 3+ exhibits high efficiency NIR emission in the 650–950 nm range upon blue excitation. At 80 K, the emission is dominated by narrow-peaks resulting from 2 E→ 4 A 2 transition. However, as the temperature rises, thermal coupling between the 2 E and 4 T 2 states leading to increased population of 4 T 2 state, the emission transforms into broad-band. At the same time, a significant decrease in lifetime is observed. This is attributed to the substantial difference in the transition probabilities of 2 E and 4 T 2 states, as well as the initiation of the nonradiative process, specifically the crossover from the 4 T 2 to the 4 A 2 state. Luminescence thermometers based on both luminescence intensity ratio (LIR) and lifetime of Ba 1.3 Ga 12 O 19.3 : 0.45 % Cr 3+ are proposed. High relative sensitivities of 6.78 %·K −1 at 113 K, and above 1 %·K −1 until 293 K is achieved from the LIR-based thermometer, and high values (ca. 1 % K −1 ) over a wide temperature range of 173–573 K are achieved from the lifetime readout.