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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]

Synergistic doping of the metastable Gd3Al5O12:Ce garnet with a Ca2+/Hf4+ pair and Sc3+ to form Gd2.97−xCaxHfxScyAl3O12:0.03Ce (x = 0.5–2.0, y = 0.0–1.5, x + y = 2.0) solid solution was conducted for the structural stabilization and photoluminescence manipulation. The site selection of Ca2+/Hf4+/Sc3+ dopants and the effects of doping on the crystal structure, local coordination, band structure and Ce3+ luminescence were revealed in detail with the results of XRD, Rietveld refinement, TEM, and UV-Vis/photoluminescence spectroscopy. A decrease in Ca2+/Hf4+ and an increase in the Sc3+ content were observed to shrink the lattice, widen the bandgap of the garnet host, red-shift the excitation/emission wavelength, broaden the emission band and shorten the fluorescence lifetime of Ce3+. The spectral changes were rationalized by considering the local coordination and crystal field splitting of the Ce3+ 5d energy level. Application of typical Gd0.97Ca2Hf2Al3O12:0.03Ce (x = 2.0, y = 0) cyan and Gd2.47Ca0.5Hf0.5Sc1.5Al3O12:0.03Ce (x = 0.5, y = 1.5) greenish-yellow phosphors in w-WLED lighting produced low correlated color temperatures of ∼3842 and 3514 K, high color rendering indices of ∼88 and 93 and favorable luminous efficacies of ∼32.9 and 14.7 lm/W under the excitation of 395 nm n-UV and 450 nm blue LED chips, respectively. [ABSTRACT FROM AUTHOR]

Systematic crystallization of KLn(MoO4)2 double molybdate micro/nanocrystals was achieved in this work for the family of lanthanide elements (excluding Pm) and Y via hydrothermal reaction under the optimized conditions of pH = 7, Mo/Ln molar ratio R = 5 and 200 °C, with which the intrinsic influence of lanthanide contraction on phase preference, crystallite morphology (size/shape) and crystal structure was clearly revealed. Extended synthesis also produced KLa1−xEux(MoO4)2 (KLM:xEu) and KY1−yEuy(MoO4)2 (KYM:yEu) red phosphors, and detailed spectral analysis found that the layered structure of orthorhombic KYM allows Eu3+ to have a high quenching content of ∼70 at% (y = 0.7) and higher quantum efficiency and thermal stability of luminescence. Application also indicated that the KYM:0.7Eu optimal phosphor has the potential for optical temperature sensing with the thermally coupled 5D0 and 5D1 energy levels of Eu3+. [ABSTRACT FROM AUTHOR]

Submicron sized, monodispersed spheres of Mn2+, Yb3+/Er3+ and Mn2+/Yb3+/Er3+ doped α-NaYF4 were easily autoclaved from mixed solutions of the component nitrates and ammonium fluoride (NH4F), in the presence of EDTA-2Na. Detailed characterizations of the resultant phosphors were obtained using XRD, Raman spectroscopy, FE-SEM, HR-TEM, STEM, PLE/PL spectroscopy, and fluorescence decay analysis. Finer structure and better crystal perfection was observed at a higher calcination temperature, and the spherical shape and excellent dispersion of the original particles was retained at temperatures up to 600 °C. Under the 980 nm infrared excitation, the Yb3+/Er3+-doped sample (calcined at 400 °C) exhibits a stronger green emission centered at ∼524 nm (2H11/2→4I15/2 transition of Er3+) and a weaker red emission centered at ∼657 nm (4F9/2→4I15/2 transition of Er3+). A 200 °C increase in the temperature from 400 °C to 600 °C resulted in the dominant red emission originating from the 4F9/2→4I15/2 transition of Er3+, instead of the previously dominant green one. Mn2+ doping induced a remarkable more enhanced intensity at ∼657 nm and ∼667 nm (red emission area) than that at ∼524 nm and ∼546 nm (green emission area), because of the non-radiative energy transfer between Mn2+ and Er3+. However, a poor thermal stability was induced by Mn2+ doping. The observed upconversion luminescence of the samples calcined at 400 °C and 600 °C followed the two photon process and the four photon process, respectively. [ABSTRACT FROM AUTHOR]

Crystallization of the Ln2(OH)5NO3·nH2O layered hydroxide (LLnH) is the most difficult for the three smallest lanthanide ions of Tm, Yb and Lu. By applying a novel two-step crystallization technique, which involves chemical precipitation at a freezing-temperature of ∼4 °C and subsequent Ostwald ripening at 50 °C for Tm and Yb and 65 °C for Lu, the three compounds have been obtained in a phase-pure form without the use of any mineralizer. The resulting LTmH and LYbH (n∼ 1.5) were shown to accommodate free NO3− anions in the interlayer gallery, which are readily exchangeable by DS− (C12H25OSO3−). Delamination of the DS− derivatives in formamide produced micron-sized nanosheets of ∼1.7 nm thick. A similar anion exchange was found to hardly proceed for LLuH even at 65 °C, owing to the direct coordination of the interlayer NO3− with the Lu3+ center. [ABSTRACT FROM AUTHOR]

Ultra-thin nanosheets (2–6 nm) of the (Y1−xEux)2(OH)5NO3·nH2O layered rare-earth hydroxide (LRH), directly crystallized without exfoliation were employed for the first time as a sacrificial precursor to synthesize (Y1−xEux)PO4 orthophosphate red phosphors via nano-conversion, and anion exchange of both the hydroxyls and NO3− in the LRH with the phosphate ions from diammonium hydrogen phosphate ((NH4)2HPO4) is discussed. Detailed characterization of the materials was performed by the combined techniques of XRD, FTIR, TG/DSC, FE-SEM, HR-TEM, and photoluminescence spectroscopy. The (Y1−xEux)PO4 phosphors, with crystallite sizes of up to ∼20 nm, were found to exhibit stronger 5D0→7F2 (621 nm) than 5D0→7F1 (595 nm) emissions under charge transfer excitation (236 nm) owing to the nano-size effect. The optimal Eu3+ content was determined to be ∼10 at% (x = 0.10), and concentration quenching of luminescence was analyzed to result from exchange interactions. The effects of the Eu3+ content and annealing temperature on the structural features and luminescence properties of the (Y1−xEux)PO4 nanophosphors were discussed in detail, including emission intensity, the asymmetry factor of luminescence, fluorescence lifetime, and CIE chromaticity coordinates. [ABSTRACT FROM AUTHOR]