Impact of ligand environment on optical, luminescence and thermometric behavior of A 3 (PO 4 ) 2 :Sm 3+ (A = Ca, Sr) phosphors.

The present study investigates the impact of the ligand environment on the luminescence and thermometric behavior of Sm 3+ doped A 3 (PO 4 ) 2 (A = Sr, Ca) phosphors prepared by combustion synthesis. The structural and luminescent properties of Sm 3+ 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 PO 4 vibrational bands. Upon excitation with near ultraviolet light, the PL studies indicated that Sr 3 (PO 4 ) 2 :Sm 3+ phosphors exhibit a yellow light emission, whereas Ca 3 (PO 4 ) 2 :Sm 3+ phosphors exhibit an emission of orange light. The PL emission results are in accordance with the CIE coordinates, with the Sr 3 (PO 4 ) 2 :Sm 3+ phosphors showing coordinates of (0.56, 0.44), and the Ca 3 (PO 4 ) 2 :Sm 3+ phosphors displaying coordinates of (0.60, 0.40). Thermal analysis shows improved stability of Ca 3 (PO 4 ) 2 :Sm 3+ 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 Sm 3+ : the 4 F 3/2  →  6 H 5/2 transition to the 4 G 5/2  →  6 H 7/2 and 4 F 3/2  →  6 H 5/2 transition to the 4 G 5/2  →  6 H 9/2 emissions are characterized. The Ca 3 (PO 4 ) 2 :Sm 3+ phosphors are more sensitive as compared with the Sr 3 (PO 4 ) 2 :Sm 3+ 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.