Chromium(III)-Doped Fluoride Phosphors with Broadband Infrared Emission for Light-Emitting Diodes

Two types of infrared fluoride phosphors, Cr³⁺-doped K₃AlF₆ and K₃GaF₆, were developed in this research. The K₃Al_1-F₆:xCr³⁺ and K₃Ga_1-F₆:yCr³⁺ fluoride phosphors were proven to be pure phase via X-ray diffraction refinement, which demonstrated that the procedure can be applied to large-scale production. Electron paramagnetic resonance measurements indicated that Cr³⁺ ions in cubic with respect to noncubic are coupled better with K₃GaF₆ than with K₃AlF₆. The main differences between these two phosphors, the site symmetry and pressure behavior of the spectra, were obtained in temperature- and pressure-dependent spectra. According to the calculation results, Cr³⁺ in fluorine coordination at ambient pressure indicates an intermediate crystal field. For the phosphor-converted light-emitting diodes (LEDs) fabricated from these two phosphors, the spectral range is from 650 to 1000 nm, which resulted in a radiant flux of 7-8 mW with an input power of 1.05 W. The research reveals detailed luminous properties, which will lead to a new way of studying Cr³⁺-doped fluoride phosphors and their application in LEDs.