Samarium doped apatite-type orange-red emitting phosphor Ca_5(PO_4)_2SiO_4 with satisfactory thermal properties for n-UV w-LEDs

A novel single-phase Sm³⁺ activated Ca₅(PO₄)₂SiO₄ phosphor was successfully fabricated via a conventional solid-state method, which can be efficiently excited by near ultraviolet (n-UV) light-emitting chips. The crystal structure and luminescence properties were characterized and analyzed systematically by using relevant instruments. The Ca₅(PO₄)₂SiO₄:Sm³⁺ phosphor shows an orange-red emission peaking at 600 nm under the excitation of 403 nm and the optimal doping concentration of Sm³⁺ is determined to be 0.08. The critical distance of Ca₅(PO₄)₂SiO₄:0.08Sm³⁺ is calculated to be 1.849 nm and concentration quenching mechanism of the Sm³⁺ in Ca₅(PO₄)₂SiO₄ host is ascribed to energy transfer between nearest-neighbor activators. The decay time of Ca₅(PO₄)₂SiO₄: 0.08Sm³⁺ is determined to be 1.1957 ms. In addition, the effect of temperature on the emission intensity was also studied, 72.4% of the initial intensity is still preserved at 250 °C, better thermal stability compared to commercial phosphor YAG:Ce³⁺ indicates that Ca₅(PO₄)₂SiO₄:0.08Sm³⁺ has excellent thermal stability and active energy is deduced to be 0.130 eV. All the results demonstrate that orange-red emitting Ca₅(PO₄)₂SiO₄:0.08Sm³⁺ phosphor exhibits good luminescent properties. Owing to the excellent thermal quenching luminescence property, Ca₅(PO₄)₂SiO₄:0.08Sm³⁺ phosphor can be applied in n-UV white light emitting diodes and serve as the warm part of white light.