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We successfully synthesized (Gd0.94−xTb0.06Mx)PO4 (M: Al and Zn; 0 ≤ x ≤ 0.06) green phosphors by ultrasonic spray pyrolysis and investigated their photoluminescence characteristics. The synthesized (Gd0.94−xTb0.06Mx)PO4 phosphor powders showed a spherical morphology and a smooth surface. The phosphors emitted a green light due to the transition from 5D4 to 7Fj of Tb3+ (j = 3–6) at 489, 544, 585, and 621 nm, respectively. The partial incorporation of Al or Zn for Gd up to x = 0.45 in (Gd0.94Tb0.06)PO4 phosphors yielded a significant rise in the emission intensity. The (Gd0.895Tb0.06Al0.045)PO4 and (Gd0.895Tb0.06Zn0.045)PO4 phosphors showed 31 and 13% stronger emission intensity at 544 nm, respectively, compared to (Gd0.94Tb0.06)PO4 phosphor.

The solution combustion method is used to synthesize nanocrystalline (Y0.5Gd0.5)PO4:Eu0.06 phosphor powders. The crystal structure and photoluminescence properties of (Y0.5Gd0.5)PO4:Eu0.06 phosphors are significantly influenced by the calcination temperature. The amount of the tetragonal xenotime structure increases with an increase of the calcination temperature. The higher calcination temperature yields the higher value of (5D0 → 7F2)/(5D0 → 7F1), improving the color purity, which originates from the phase transformation from the monoclinic monazite structure to the tetragonal xenotime structure. The (Y0.5Gd0.5)PO4:Eu0.06 phosphor calcined at 1300 °C emits the purest red color. We need to obtain the tetragonal xenotime structure for improved red color purity.

The microstructure and photoluminescence properties of Gd0.94-xAlxEu0.06VO4 (0≤x≤0.04) phosphors with various Al3+ contents were investigated. The phosphors showed a nanocrystalline nature and a high-quality powder characteristic. The crystallite sizes of the phosphors were calculated to be 46-48 nm. The annealed Gd0.94-xAlxEu0.06VO4 phosphors crystallized in the tetragonal structure. In the emission spectra, several emission peaks were observed over the measured wavelength range (500-750 nm), which were caused by the difference in the transitions of Eu3+ ions, depending on the local symmetry (5D0 → 7Fj, j = 1, 2, 3, and 4). The strongest emission peak was located at 619 nm, providing a high-purity red emission. The doped Al3+ yielded significantly enhanced the emission intensity. The most intense high-purity red emission was obtained for Gd0.93Al0.01Eu0.06VO4.

High-quality Zn-free and added GdPO 4 :Tb 3 green phosphors, i.e., fine size as well as smooth and spherical morphologies, were synthesized by ultrasonic spray pyrolysis. The influence of Zn 2+ content and annealing temperature on the photoluminescence properties of the GdPO 4 :Tb 3 phosphors annealed at 800–1100 °C was investigated. The addition of Zn 2+ for Gd 3+ was highly effective for improving the photoluminescence properties of GdPO 4 :Tb 3 . The Zn added GdPO 4 :Tb 3 phosphors with Zn/Gd = 0.045/0.805 showed the strongest emission of the prepared phosphors. The emission intensity at 544 nm for the GdPO 4 :Tb 3 phosphors with Zn/Gd = 0.045/0.805 annealed at 900 °C was 496% stronger than that at 800 °C.

The red-emitting (Y 1− x Gd x ) 0.94 Eu 0.06 VO 4 (0 ≤ x ≤ 1.0) phosphors were synthesized by ultrasonic spray pyrolysis. The (Y 1− x Gd x ) 0.94 Eu 0.06 VO 4 (0 ≤ x ≤ 1.0) phosphors had the tetragonal xenotime structure with a space group of I4 1 /amd (1 4 1). The calculated crystallite sizes of the annealed phosphors ranged from 58 to 68 nm. In this study, we discussed the photoluminescence properties of the (Y 1− x Gd x ) 0.94 Eu 0.06 VO 4 phosphors under VUV excitation, depending on Gd content. The emission intensity of the (Y 1− x Gd x ) 0.94 Eu 0.06 VO 4 phosphors increased with increasing Gd content up to x = 0.5, and then decreased with a further increase in Gd content. The purest red color was obtained for the (Y 0.5 Gd 0.5 ) 0.94 Eu 0.06 VO 4 phosphors.

The red-emitting (Y 1− x − y M x Eu y )BO 3 (M = Al, Zn, and La, 0 ≤ x ≤ 0.1, 0.04 ≤ y ≤ 0.16) phosphors were synthesized by ultrasonic spray pyrolysis and their photoluminescence characteristics were studied under VUV excitation. The emission intensity was significantly improved by adding metal (M) dopants because they acted as an intermediator for the transfer of excitation energy from the host lattice to the activator Eu 3+ . The emission intensity of the (Y 0.94− x M x Eu 0.06 )BO 3 increased up to x = 0.025 with increasing metal concentration and then decreased with a further increase in metal concentration owing to the concentration quenching effect. The Eu 3+ - and Al 3+ -co-doped (Y 0.975− y Al 0.025 Eu y )BO 3 showed the highest emission intensity at a lower Eu content ( y = 0.06), when compared to that ( y = 0.13) of singly Eu 3+ -doped (Y 1− y Eu y )BO 3 because of the sensitization effect of Al 3+ ions.