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The dicarboxylate anions of tartrate (C4H4O62−, Tar2−), malate (C4H4O52−, Mal2−), and succinate (C4H4O42−, Suc2−) were originally used as morphology/structure modifiers in the hydrothermal crystallization of YPO4, and both hexagonal (h-) and tetragonal (t-) structured crystals with multiform morphologies of high uniformity were selectively synthesized. The materials were characterized by the combined techniques of XRD, FE-SEM, TEM, FT-IR, TG, and optical spectroscopy, and the mechanisms of phase/morphology evolution were expatiated. It was clearly shown that Tar2− may induce an inverse phase transformation of YPO4 from the thermodynamically stable tetragonal structure (nanoparticles) to the metastable hexagonal structure (microprisms), and a series of controlled experiments exhibited that the performance of Tar2− was strongly affected by the experimental parameters of Tar2−/PO43−/Y3+ molar ratio, solution pH, hydrothermal temperature, and reaction time. In comparison with Tar2−, Mal2− induced the direct crystallization of h-YPO4 microprismatic crystals while Suc2− restricted the 1-D growth of t-YPO4 nanocrystals. For the samples calcined at 700 °C, the down-conversion photoluminescence of Eu3+ in h-YPO4 and t-YPO4 and the up-conversion luminescence of the (Yb/Er)3+ couple in t-YPO4 were also comparatively studied and elucidated in detail. [ABSTRACT FROM AUTHOR]

● Multiform (Y 0.95 Eu 0.05)PO 4 crystals were attained via hydrothermal reaction. ● Increasing MA content leads to a tetragonal (t-) to hexagonal (h-) phase transition. ● A higher pH or PO 4 3- content favors the crystallization of t-(Y 0.95 Eu 0.05)PO 4. ● The (Y 0.95 Eu 0.05)PO 4 phosphors showed structure/morphology-dependent luminescence. [Display omitted] With maleic acid (MA) as an original and efficient structure/morphology modifier, tetragonal (t-) and hexagonal (h-) structured (Y 0.95 Eu 0.05)PO 4 nano/microcrystals with the diverse morphologies of nanoparticles, nanospindles, nanosquares, nanodisks and microprisms have been successfully synthesized via hydrothermal reaction at 180 °C for 24 h. The systematic study demonstrated that solution pH, MA/(Y 0.95 Eu 0.05)3+ molar ratio and PO 4 3-/(Y 0.95 Eu 0.05)3+ molar ratio are three crucial factors that synergistically determine phase structure and crystal shape/size of the product, and the underlying mechanisms were proposed. Photoluminescence of the (Y 0.95 Eu 0.05)PO 4 crystals was revealed to be strongly morphology/structure dependent, which was discussed in detail in terms of excitation, emission, asymmetry factor of luminescence, quantum yield, fluorescence decay, emission color and thermal stability. [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]