Charge compensated CaSr2(PO4)2:Sm3+, Li+/Na+/K+ phosphor: Luminescence and Thermometric studies

A series of Sm 3+ doped and Li + /Na + / K + co-doped CaSr 2 (PO 4 ) 2 phosphors were prepared via solution combustion synthesis. The luminescence and thermometric studies of the phosphors were investigated to explore the phosphor for potential application in high power light emitting diodes and optical thermometry. The diffraction pattern showed that the structure of the phosphor is in accordance with the rhombohedral phase of CaSr 2 (PO 4 ) 2 having a space group R3c(161). Under near-ultraviolet (n-UV) excitation, the phosphors exhibited characteristic emission of the Sm 3+ ions with the main orange-red peak at 600 nm. The host of the phosphor, according to the diffuse reflectance studies, was a broad bandgap material that successfully accommodated the dopants. Co-doping of alkali metal ions (Li + , Na + , K + ) improved the fluorescence intensity significantly. The computed Commission Internationale de l'éclairage coordinates (0.59, 0.40) for the phosphors were found to be in the orange-red region of the spectrum with a high color purity of 97.3%. The temperature dependent photoluminescence studies demonstrated that the prepared phosphor had high thermal stability when working in the region of 303 K to 473 K. The phosphor was also explored for thermometry, for this the temperature dependent spectra of the phosphor were measured up to 973 K. The fluorescence intensity ratios 4 F 3/2 → 6 H 5/2 (531 nm) to 4 G 5/2 → 6 H 5/2 (562 nm), 4 F 3/2 → 6 H 5/2 (531 nm) to 4 G 5/2 → 6 H 7/2 (600 nm) and 4 F 3/2 → 6 H 5/2 (531 nm) to 4 G 5/2 → 6 H 9/2 (645 nm), were measured as a function of temperature in the range of 323→973 K. At 725 K, the greatest temperature sensitivity of 2.257 × 10 -4 K -1 was attained for the 4 F 3/2 → 6 H 5/2 to 4 G 5/2 → 6 H 5/2 ratio. The high thermal stability and good temperature sensitivity of the CaSr 2 (PO 4 ) 2 :Sm 3+ , Li + phosphors demonstrated that the material can be a potential candidate for n-UV-excited white light emitting diodes and optical thermometry applications. • Charge compensated CaSr 2 (PO 4 ) 2 :Sm 3+ , Li + /Na + /K + phosphors were synthesized. • Highly pure and thermally stable emission was realized upon UV excitation. • The phosphors were examined for luminescence thermometry.