A potential red-emitting phosphor CaSrAl2SiO7:Eu for near-ultraviolet light-emitting diodes

A novel red-emitting phosphor CaSrAl₂SiO₇:Eu³⁺ was firstly synthesized through the high temperature solid state reaction at 1300 °C. The structure, diffuse reflection spectra, photoluminescence spectra, color-coordinate parameters and quantum efficiencies (QE) of phosphors were investigated. The obtained CaSrAl₂SiO₇:Eu³⁺ phosphors have the same structure with that of the Ca₂Al₂SiO₇ and Sr₂Al₂SiO₇ phosphor, which have the melilite structure. Optical properties were studied as a function of Eu³⁺ concentration x, when x>0.14, the intensity of absorption of the f–f transitions of Eu³⁺ at 393 nm is stronger than that of the broad charge transfer transition band (CTB) around 254 nm, and which matches well with the output lights of NUV–LEDs, whereas, the concentration of Eu³⁺x≤0.14, the absorption of 393 nm is weaker than that of CTB. The underlying reason of Eu³⁺ concentration on their luminescent properties was investigated and discussed in detail. As a result, comparing with the commercial red phosphor Y₂O₂S:Eu³⁺, the CaSrAl₂SiO₇:xEu³⁺ (x>0.14) phosphor exhibited excellent color purity and much higher brightness and could be considered as promising red phosphors for NUV–LEDs.