Near-infrared (NIR) II region (1000–1700 nm) lighting sources possess special potential for temperature sensing and quantitative composition analysis. However, it is a challenge to tune the luminescence toward such long wavelength NIR-II emission. Herein, Cr 4+ ions occupation is designed and verified in olivine-type CaYGaO 4 as [CrO 4 ] tetrahedron by site occupancy confinement. Under 620 nm red light excitation, the phosphors display broadband NIR-II emission centered at 1330 nm with a full width at half maximum (FWHM) of 233 nm, resulting from spin-allowed 3 T 2 to 3 A 2 transition of Cr 4+ ions in T d symmetry. The optical thermometry application is demonstrated by decoding the spectral shift and decay times varying with temperature, and the maximum relative sensitivities are 5.82% and 0.78% K −1 , respectively. Furthermore, a flexible film containing CaYGaO 4 :Cr 4+ is fabricated to implement the non-invasive detections of fillet temperature and NH 3 concentration in ammonia. This work represents a step toward developing next-generation NIR-II luminescence materials and widens non-invasive detection applications.
Tao Hu,Zelong Jiang,Bo Wang,Ting Yu,Dawei Wen,Qinguang Zeng,Yan Gao
Fine control of the photon emission of Eu2+ activated luminescent materials is essential for advanced optoelectronic applications. However, it remains difficult to design blue light excitable Eu2+ doped oxide red phosphors due to the ionicity of the oxide ions. Herein, we have mechanistically demonstrated that an Eu2+ incorporated CaYGaO4 phosphor exhibits efficient red emission at 650 nm, as a result of the Eu2+ 4f65d1 electronic state experiencing strong crystal field splitting. DFT calculations reveal that the Eu2+ ion is energetically favored in the octahedral Ca2+ site, which is responsible for the fascinating optical properties. We have also demonstrated a strategy of post thermal annealing for improving both the emission efficiency and thermal emission quenching properties of this newly developed red phosphor. By employing the as-fabricated phosphor as a red color convertor, a warm white lighting device with a high color render index of 89.7 and low corrected color temperature of 3780 K was constructed. Our findings not only provide a promising red phosphor candidate for lighting of excellent quality, but also help to stimulate new routes for designing and improving the photon emission of rare-earth luminescent materials.
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