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Doping Gd2LuAl5O12:Ce with a Ca2+/Si4+ pair produced a series of Gd1.97−xLuCaxAl5−xSixO12:0.03Ce (x = 0.0–1.2) garnet new phosphors, and remarkable regulation of the crystal structure and Ce3+ luminescence was achieved. Rietveld refinement and spectral analysis revealed that greater incorporation of Ca2+/Si4+ led to a higher lattice rigidity by cell contraction, a narrower bandgap, a longer average bond length/less distortion of the [CeO8] dodecahedron and decreased centroid shift/crystal field splitting of the Ce3+ 5d energy level. A blue-shifted 4f–5d1 transition, a narrower emission band, improved thermal stability of luminescence and a shorter fluorescence lifetime were observed with increasing Ca2+/Si4+ content. Applying the yellowish-green-emitting Gd0.77LuCa1.2Al3.8Si1.2O12:0.03Ce optimal phosphor (x = 1.2), together with a commercial CaAlSiN3:Eu red phosphor, in 450 nm-excited LED lighting produced a low CCT of ∼3625 K and a high CRI/R9 of ∼95.2/94.8, indicating that the phosphor has application potential in high-performance w-WLED. [ABSTRACT FROM AUTHOR]

In the case of spark plasma sintered (SPSed) oxides, it is known that carbon contamination and oxygen vacancies are introduced during the sintering process due to the SPS characteristic of a carbon-rich environment. The introduction of carbon contamination and oxygen vacancies had a direct effect on the transmittance, and the annealing process mostly recovered the low transmittance of sintered bodies. It also affected the luminescence characteristics. The luminescence intensity of sintered bodies, which was very low due to carbon contamination and oxygen vacancies, could be dramatically improved through the annealing process. In the specimens with longer holding times during SPS, the grain size was increased, and the porosity was also significantly reduced, resulting in higher intensity improvements. Through the SPS process, the sintered body was effectively densified, and the annealing could compensate for the drawback of SPS and enable better luminescence properties. [ABSTRACT FROM AUTHOR]

A series of garnet-type Li 6 CaLa 2(1- x) Nb 2 O 12 : x RE phosphors (LCLN: x RE, RE = Pr, Sm, Tb and Dy) were prepared via sol-gel processing and subsequent calcination for the first time, with the course of phase evolution and the characteristics of the LCLN host and RE3+ luminescence being investigated in detail. It was found that ∼900–1000 °C is a suitable temperature for precursor calcination to produce the garnet phase and LCLN has a relatively low phonon energy (∼725 cm−1) and a relatively wide bandgap (∼4.53 eV) for luminescence. The LCLN:0.012Pr, LCLN:0.04Sm, LCLN:0.06 Tb and LCLN:0.06Dy typical phosphors were analyzed to have dominant excitation/emission bands at ∼278/489, 265/614, 268/549 and 264/581 nm, emission colors of white, orange, green and yellowish white, and fluorescence lifetimes of ∼0.43, 0.74, 0.90 and 0.44 ms, respectively. Temperature-dependent photoluminescence found that the four phosphors maintained ∼28, 37, 45 and 56% of their room-temperature intensities at 423 K, with activation energies for thermal quenching of ∼0.37, 0.29, 0.34 and 0.25 eV, respectively. The results demonstrated that the Li-stuffed LCLN garnet could be a suitable host for UV excitable multicolor phosphors. • ∼900–1000 °C is an appropriate temperature for precursor calcination to derive Li 6 CaLa 2 Nb 2 O 12 (LCLN) garnet. • The LCLN host is suitable for luminescence purposes. • The photoluminescence of Pr3+, Sm3+, Tb3+ and Dy3+ activators was comprehensively elaborated in LCLN. • The concentration quenching of Sm3+ luminescence in LCLN is dominantly resulted from electric dipole-dipole interaction. [ABSTRACT FROM AUTHOR]

• Air-calcined TbAG:Eu phosphor exhibits red luminescence of Eu3+ (∼575–725 nm) mostly via Tb3+ → Eu3+ energy transfer. • The optimal Eu3+ content of air-calcined TbAG:Eu is about 3 at.%. • ∼63% of the Eu in (Tb 0.97 Eu 0.03)AG was reduced to Eu2+ by calcination in hydrogen at 1500 °C. • Hydrogen-reduced TbAG:Eu exhibits cyan luminescence, with chromaticity coordinates of around (0.286, 0.381), by Tb3+, Eu3+ and Eu2+. • Forward and backward energy transfer among Tb3+, Eu2+ and Eu3+ was suggested to occur via electron exchange interaction. Calcination of coprecipitated precursors at 1500 °C in air produced (Tb 1- x Eu x) 3 Al 5 O 12 garnet phosphors (x = 0.0025-0.05) that exhibit dominant excitations via 4f8 → 4f75d1 (E 1-4) and 7F 6 → 5D 3,4 transitions of Tb3+ and negligible excitation of Eu3+. Exciting the phosphors with 275 nm light (E 2 transition of Tb3+) produced the typical 5D 0 → 7FJ red emissions of Eu3+. Annealing the x = 0.03 sample in hydrogen at 1500 °C reduced ∼62.8% of Eu3+ to Eu2+ and yielded a cyan phosphor that simultaneously exhibits the luminescence of Eu3+ (red), Tb3+ (green) and Eu2+ (broad-band, 400–725 nm) under 327 nm excitation (E 1 transition of Tb3+). The (Tb 0.97 Eu 0.03)AG optimal phosphors calcined in air and hydrogen were assayed to have external/internal quantum efficiencies (in percentage) of ∼23.2/24.2 and 18.6/23.7, respectively. Luminescence features of the two types of phosphors were investigated in detail, and the energy transfer among Tb3+, Eu2+ and Eu3+ ions was discussed. [ABSTRACT FROM AUTHOR]

• Li 6 CaLa 2 Nb 2 O 12 (GCN) garnet was identified to be a favorable host for efficient red luminescence of Eu3+. • The optimal Eu3+ content is ~35 at.% relative to La3+. • The GCN:Eu phosphor is efficiently excitable with either blue or NUV light. • The GCN:0.35Eu optimal phosphor has an excellent thermal stability and favorably high quantum yield. Li 6 CaLa 2 Nb 2 O 12 garnet is known as an electrolyte for Li+-batteries. The sol–gel processing of this work yielded a series of phase pure Li 6 CaLa 2(1− x) Nb 2 O 12 : x Eu3+ garnet phosphors (LCLNG: x Eu; x = 0–0.40) that are efficiently excitable with either near-ultraviolet (NUV, ~350–400 nm) or blue (~450–475 nm) light to produce dominantly strong 610 nm red emission. Increasing Eu3+ substitution for La3+ (larger x) led to smaller cell constant and lower symmetry of the (La/Ca)O 8 dodecahedron, as revealed via Rietveld structure refinement, and meanwhile narrower bandgap. The excitation/emission behaviors and high quenching concentration of Eu3+ (x = 0.35) were interpreted for the phosphor series by considering bandgap energy, (La/Ca)O 8 distortion and local arrangement of atoms. The LCLNG:0.35Eu optimal phosphor was analyzed to have absolute quantum yields of ~51% (λ ex = 393 nm) and 65% (λ ex = 463 nm), fluorescence lifetime of ~0.70 ms and color coordinates of around (0.65, 0.35) at room temperature and to be able to retain as high as ~85% of its room-temperature intensity at 423 K for the 610 nm emission. Application of LCLNG:0.35Eu further indicated that this phosphor has the potential to be used in NUV-excited LEDs. [ABSTRACT FROM AUTHOR]