Photoluminescence characteristics and optical temperature sensing of orange-red emitting oxyapatite phosphor Ca3La7(SiO4)5(PO4)O2:Sm3+

Abstract

In this study, we successfully synthesized a series of oxyapatite phosphors, Ca₃La₇(SiO₄)₅(PO₄)O₂ doped with Sm³⁺ ions, using a high-temperature solid-state reaction method. The synthesis process involved varying the concentrations of Sm³⁺ dopants to investigate their impact on the phosphors' structural and luminescent properties. The phase purity of the synthesized material was evaluated using X-ray diffraction (XRD) analysis, which confirmed a hexagonal crystal structure. Additionally, the XRD results validated the high phase purity of the prepared oxyapatite phosphors and demonstrated the successful incorporation of Sm³⁺ ions into two separate crystallographic sites within the lattice. Raman scattering spectra revealed distinct vibrational modes corresponding to the stretching and bending vibrations of the PO₄ and SiO₄ groups in the structure of the synthesized material. In addition, scanning electron microscopy (SEM) illustrated the morphology of the sample. The photoluminescence excitation and emission spectra of Ca₃La₇(SiO₄)₅(PO₄)O₂:Sm³⁺ phosphors were investigated. Upon excitation with near-ultraviolet (near-UV) light, the phosphors exhibited four distinct emission peaks at wavelengths of 565 nm, 598 nm, 648 nm, and 708 nm. Ca₃La₇(SiO₄)₅(PO₄)O₂:Sm³⁺ phosphors exhibit strong orange-red emission centered at 598 nm, attributed to multipole–multipole interactions, and demonstrate rapid decay rates, making them promising candidates for temperature sensing and supplementary solid-state lighting applications. The CIE chromaticity coordinates of phosphors with varying Sm³⁺ concentrations consistently fall within the orange-red region, confirming their characteristic light emission. Consequently, the synthesized Ca₃La₇(SiO₄)₅(PO₄)O₂:Sm³⁺ phosphor shows significant potential for use in white light-emitting diodes (WLEDs). The relative sensitivity of the Ca₃La₇(SiO₄)₅(PO₄)O₂:6 at% Sm³⁺ was measured to be approximately 0.212% K⁻¹ at 293 K, underscoring their potential for temperature sensing applications. This sensitivity is distinct from thermal quenching, which is critical for LED performance. Collectively, these findings demonstrate the suitability of the novel synthesized oxyapatites for applications in solid-state lighting and optical thermometry.