A new strategy to the phosphors for plant growth LEDs: Far red emission from the Ca9MY0.667 (PO4)7 (M = Li, Na):Eu3+ phosphors due to the Eu3+: 5D0 → 7F4 transition

Abstract The novel red-emitting Ca9MY0.667(PO4)7 (M = Li, Na) (CMYPO):xEu3+ (x = 0.02, 0.04, 0.07, 0.12, 0.16, 0.26, 0.35, and 0.44) phosphors were successfully synthesized by a high-temperature solid-phase reaction. The samples were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectra, ultraviolet–visible diffuse reflectance (UV–Vis DR) spectra, photoluminescence excitation (PLE) and emission (PL) spectra. It is found that the samples can be excited by near-ultraviolet (NUV) and blue light. The intense PL peaks were centered at 614 nm due to the 5D0 → 7F2 transition. Interestingly, 5D0 → 7F4 (700 nm) far-red emission matches with the far-red absorption wavelength required for plant photosensitive pigments red (PR) and far-red (PFR) light. Moreover, the PL intensity of Ca9NaY0·667(PO4)7 (CNYPO):Eu3+ is higher than that of Ca9LiY0·667(PO4)7 (CLYPO):Eu3+. In addition, the band gaps of CLYPO and CNYPO were determined to be 3.81 and 3.61 eV, respectively. Finally, the International Commission on Illumination (CIE) chromaticity of phosphors are located in red region. The results showed that the phosphors are considered as the potential luminescence materials in white light emitting diodes (w-LEDs). Impressively, the as-prepared samples can provide reference for the development of Eu3+-doped phosphors that can be used for plant growth LEDs.