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A series of Ba3-x ( VO4 )2 : xSm3+ (x = 0.02-0.16) phosphors were synthesized using the molten salt method with KCl as the salt. The effects of synthesis conditions as well as Sm3+ doping concentration on the phase structure and luminescence properties of the sample were investigated in detail. The temperature sensing characteristics of the sample were also studied. The optimum reaction conditions for synthesizing the sample are calcination temperature of 900 °C, calcination time of 1h, and a mass ratio of raw materials to molten salt of 1 : 3. The obtained sample has high phase purity and crystallinity. The micromorphology of the sample is lamellar with a thickness of about 1.53 mm. Upon the ultraviolet excitation of 318 nm, the broad emission from the VO43- groups and characteristic emissions from Sm3+ can be observed simultaneously in the emission spectra of Ba3-x(VO4)2:xSm3+ phosphors, with the emission colors concentrated in the yellow-white light region. With the increase of Sm3+ doping concentration (x) from 0.02 to 0.16, the intensity of the characteristic emission peak of Sm3+ first increases and then decreases, reaching its maximum value when x =0.10. The dominant mechanism for the concentration quenching in Ba3-x(VO4)2 :xSm3+ phosphors is attributed to the dipole-dipole (d-d) interaction. Moreover, for Ba2.9 (VO4 )2 : 0.10Sm3+ phosphors, it is found that the fluorescence intensity ratio of Sm3+ (652 nm) and VO43- groups (504 nm) shows a significant temperature dependence in the temperature range of 298-473 K. Its maximum absolute and relative temperature sensor sensitivities are 0.36/K and 1.99%/K, respectively. The results indicate that Sm3+ doped Ba3(VO4)2 phosphors exhibit excellent temperature sensing performance and potential applications in non-contact optical thermometry. [ABSTRACT FROM AUTHOR]

A series of color tunable NaCa2-xMg2 (VO4)3 : xEu3+ (0≤x≤0. 10) phosphors were synthesized by molten salt method using cheap NaCl as molten salt. The effects of synthesis conditions and Eu3+ doping on the structure and luminescence properties of the samples were investigated in details. The results show that the optimum reaction conditions for the synthesis of NaCa2Mg2 (VO4)3 are reaction temperature of 800 °C, reaction time of 0. 5 h and mass ratio of raw material to molten salt of 1:3. The obtained samples are NaCa2Mg2 (VO4)3 pure phase with higher crystallinity. The micromorphology of the samples changed from coral-like to smooth irregular polyhedron with the increase of temperature. Eu3+ doping has little effect on the crystal structure of NaCa2 Mg2 ( VO4)3, but great effect on its luminescence properties. With the increase of Eu3+ concentration (x), the characteristic emission band intensity of VO43- gradually decreases, while the characteristic emission peak intensity of Eu3+ first increases and then decreases, reaching the maximum when x = 0. 06. Therefore, the luminous color of the samples can be modulated by changing the Eu3+ concentration, from green to yellow-green, yellow, yellow-white and orange-red. According to the fluorescence spectrum and fluorescence lifetime analysis, it is confirmed that the energy transfer process of VO43-to Eu3+ exists in NaCa2 Mg2 (VO4)3 : Eu3+ phosphors, and the energy transfer efficiency is about 23%. The thermal stability analysis shows that when the temperature increases from room temperature (298. 15 K) to 398. 15 K, the retaining ratio of the main emission peak intensity of NaCa2 Mg1. 94 (VO4)3:0. 06Eu3+ phosphor at 614 nm is 68. 4%, showing its good thermal stability. [ABSTRACT FROM AUTHOR]