Crystal structure and luminescence properties of thermally stable Sm ³⁺ -doped Sr ₉ In(PO ₄ ) ₇ orange-red phosphor

A series of novel phosphate orange-red phosphor, Sr 9 In(PO 4 ) 7 : x Sm 3+ (0.01 < x < 0.30), were successfully synthesized from high-temperature solid-state synthesis in this work. Their crystal structure has been analyzed by the Rietveld refinement, which shows Sr 9 In(PO 4 ) 7 consists of a monoclinic cell ( C 2/ c ), which also confirms the successful doping, preferential site occupancy and local ligand environment of Sm 3+ . Luminescence properties of the samples have been systematically investigated including excitation and emission spectra, quantum efficiency, concentration quenching, fluorescence decay and temperature-dependent luminescence properties. Photoluminescence spectra exhibited typical peaks, corresponding to 4 G 5/2 → 6 H J transitions of Sm 3+ ions, where J = 5/2, 7/2, 9/2, and 11/2, respectively. Moreover, the concentration quenching result revealed that the optimal doping content of Sm 3+ was 0.15 mol, and based on the Dexter theory, the energy transfer between Sm 3+ ions was found in dipole-dipole interactions. The quantum yield of Sr 9 In(PO 4 ) 7 :0.15Sm 3+ phosphor was acceptable (58.5%). Most importantly, the emission intensity of Sr 9 In(PO 4 ) 7 :0.15Sm 3+ remains constant (>97%) below 150 °C and the configurational coordinate diagram analysis demonstrated excellent thermal stability of the Sr 9 In(PO 4 ) 7 :Sm 3+ phosphor, which is superior to that of the previously reported and commercially available phosphors. These results suggest that the Sr 9 In(PO 4 ) 7 :Sm 3+ phosphor is a promising orange-red phosphor materials for white light emitting diodes.