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

Abstract

The present study investigates the impact of the ligand environment on the luminescence and thermometric behavior of Sm3+ doped A3(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 Sr3(PO4)2:Sm3+ phosphors exhibit a yellow light emission, whereas Ca3(PO4)2:Sm3+ phosphors exhibit an emission of orange light. The PL emission results are in accordance with the CIE coordinates, with the Sr3(PO4)2:Sm3+ phosphors showing coordinates of (0.56, 0.44), and the Ca3(PO4)2:Sm3+ phosphors displaying coordinates of (0.60, 0.40). Thermal analysis shows improved stability of Ca3(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 4F3/2 → 6H5/2 transition to the 4G5/2 → 6H7/2 and 4F3/2 → 6H5/2 transition to the 4G5/2 → 6H9/2 emissions are characterized. The Ca3(PO4)2:Sm3+ phosphors are more sensitive as compared with the Sr3(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.