Realizing Antithermal Quenching Red Emission in Mn⁴⁺-Activated Rb₂NaVF₆ for Optical Thermometry Sensor Application

Currently, the development of red Mn⁴⁺-activated fluoride luminescent materials attracts a lot of attention in optical thermometry sensors, solid lighting, display, and plant growth areas. Nevertheless, the thermal stability of Mn⁴⁺-activated fluoride luminescent materials is still a crucial issue. Herein, a new red Rb₂NaVF₆:Mn⁴⁺ luminescent material with outstanding thermal stability was successfully synthesized through the facial coprecipitation method. Mn⁴⁺ ions prefer to occupy VF₆ octahedra based on the accurate Rietveld refinement results. Accordingly, the as-prepared Rb₂NaVF₆:Mn⁴⁺ exhibits a broad absorption region from 300 to 500 nm with a maximum of 468 nm, matching well with the near-ultraviolet and blue InGaN chip. Upon 468 nm excitation, Rb₂NaVF₆:Mn⁴⁺ can emit narrow-band red light at 632 nm. Notably, Rb₂NaVF₆:Mn⁴⁺ shows superior antithermal quenching properties, of which the integrated intensities at 175°C can realize as high as 140% than that at 25°C. Owing to the diverse thermal quenching behavior between anti-Stokes and Stokes emission, Rb₂NaVF₆:Mn⁴⁺ displays promising candidates in optical thermometry sensors with a relative sensitivity S_r of 0.49%. This study offers new insight into developing antithermal quenching red Mn⁴⁺-activated fluoride luminescent materials.