Ba ₃ LaNb ₃ O ₁₂ :Sm ³⁺ /g‐C ₃ N ₄ mixed phosphors for dual‐mode optical thermometry

Abstract There is a tremendous demand for noncontact temperature sensing technologies due to their fast response and accurate testing. In this work, Ba 3 LaNb 3 O 12 :Sm 3+ /g‐C 3 N 4 mixed phosphors with various compositional ratios were synthesized via a high‐temperature solid‐state reaction. Over the temperature range of 313–573 K, the luminescent intensity of g‐C 3 N 4 exhibited a decreasing trend. In contrast, the luminescent intensity of Ba 3 LaNb 3 O 12 :Sm 3+ demonstrates an antithermal quenching phenomenon due to the high structural rigidity of Ba 3 LaNb 3 O 12 . To achieve high temperature sensitivity, Ba 3 LaNb 3 O 12 :0.08Sm 3+ and g‐C 3 N 4 were mixed at an optimal 15:1 ratio, leveraging their contrasting thermal responses. The composite exhibits tunable emission, with its color shifting from cyan to orange as the temperature rises. This property enables a dual‐mode temperature sensing based on fluorescence intensity ratio (FIR) and Commission Internationale de l'Éclairage (CIE) chromaticity coordinates, achieving maximum relative sensitivities of 1.63% K −1 at 313 K and 0.34% K −1 at 573 K, respectively. Besides, the repeatability of the optimal mixed phosphors reaches 98% across variable temperature cycles. These results indicate that the Ba 3 LaNb 3 O 12 :Sm 3+ /g‐C 3 N 4 mixed phosphor exhibits high sensitivity and exceptional repeatability, demonstrating its potential for application in self‐calibrated optical thermometry.