Impact of ligand environment on optical, luminescence and thermometric behavior of A₃(PO₄)₂:Sm³⁺ (A = Ca, Sr) phosphors

The present study investigates the impact of the ligand environment on the luminescence and thermometric behavior of Sm3+ doped A(3)(PO4)(2) (A = Sr, Ca) phosphors prepared by combustion synthesis. The structural and luminescent properties of Sm3+ ions in the phosphate lattices were investigated using powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques. PXRD results of the synthesized phosphors exhibit the expected phases that are in agreement with their respective standards. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of PO4 vibrational bands. Upon excitation with near ultraviolet light, the PL studies indicated that Sr-3(PO4)(2):Sm3+ phosphors exhibit a yellow light emission, whereas Ca-3(PO4)(2):Sm3+ phosphors exhibit an emission of orange light. The PL emission results are in accordance with the CIE coordinates, with the Sr-3(PO4)(2):Sm3+ phosphors showing coordinates of (0.56, 0.44), and the Ca-3(PO4)(2):Sm3+ phosphors displaying coordinates of (0.60, 0.40). Thermal analysis shows improved stability of Ca-3(PO4)(2):Sm3+ based on lower weight reduction in thermogravimetric analysis. The effect of temperature on the luminescence properties of the phosphor has been examined upon a 405 nm excitation. By using the fluorescence intensity ratio (FIR) method, the temperature responses of the emission ratios from the Sm3+: the F-4(3/2) -> H-6(5/2) transition to the (4)G(5/2) -> H-6(7/2) and F-4(3/2) -> H-6(5/2) transition to the (4)G(5/2) -> H-6(9/2) emissions are characterized. The Ca-3(PO4)(2):Sm3+ phosphors are more sensitive as compared with the Sr-3(PO4)(2):Sm3+ phosphors. The earlier research findings strongly indicate that these phosphors hold great promise as ideal candidates for applications in non-invasive optical thermometry and solid-state lighting devices.