Synthesis and optical properties of orange–red emitting Sm3+-activated Ca9LiGd2/3(PO4)7 phosphors

The phosphors of Sm3+-activated Ca9LiGd2/3(PO4)7 are synthesized through a solid state reaction. The X-ray powder diffraction analysis, photoluminescence excitation and emission spectra, thermal quenching were applied to investigate the phase structure, luminescence, and thermal stability properties. The emission spectra of the Ca9LiGd2/3(PO4)7:Sm3+ phosphors consisted of some sharp emission peaks of Sm3+ ions centered at 562, 601, 646, 708 nm. The strongest one is located at 604 nm due to 4G5/2–6H7/2 transition of Sm3+, generating bright orange–red light. The optimum doping concentration of Sm3+ ions is measured to be 15 mol%. The critical transfer distance of Sm3+ is calculated as 20 Å. The thermal-quenching temperature is above 500 K. The CIE chromaticity coordinates of the Ca9LiGd2/3(PO4)7:0.15Sm3+ phosphor were located in the orange–reddish region. It shows strong absorption in 350–420 nm region, which has great potential red phosphors for white light-emitting diodes.