Abnormal reduction and luminescence properties of Sm2+-doped Sr5(PO4)3Cl prepared by solution combustion synthesis

Abstract Sm-doped Sr5(PO4)3Cl was prepared by a solution combustion synthesis in the air atmosphere. The pure hexagonal phases of the samples were confirmed via the XRD, Raman, and FT-IR measurements. The typical microrod shape of the products was also demonstrated by SEM, TEM, and HRTEM images. The spectral properties and lifetimes were applied to characterize the luminescence of the samples as-prepared and subsequently heated in the air atmosphere. The luminescence of as-prepared Sm-doped Sr5(PO4)3Cl contains a broad emission band and a group of narrow lines, which are ascribed to the radiative transitions of 4f5d→4f and 5D0→7FJ (J = 0, 1, 2) of Sm2+ ions, respectively. It indicates that the Sm3+ can be successfully reduced to Sm2+ ions in hexagonal Sr5(PO4)3Cl prepared by combustion synthesis. The temperature dependent luminescence spectra and decay curves of Sm2+ were measured in a very wide temperature region from 10 K to 300 K. The thermal quenching and activation energy of Sm2+ doped Sr5(PO4)3Cl were reported. The crystal field energy level diagram and excitation mechanism of Sm2+ ions-doped Sr5(PO4)3Cl were characterized by the high resolution luminescence at low temperature. The luminescence of Sm2+ in Sr5(PO4)3Cl shows a great dependence on heating temperature in the air atmosphere (50–700 °C). The heating treatments at the elevated temperature depress Sm2+ emission along with the appearance of Sm3+ ions. The temperature-induced changes in the modification of the spectral components could be applied as potential luminescence thermometry.