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Abstract Eulytite-type Ba 3 La 1- x (PO 4) 3 : x Ce3+ (x = 0–0.10) and Ba 3- y La 0.97 (PO 4) 3 :0.03Ce3+, y Mn2+ (y = 0.05–0.30) phosphors were first synthesized via gel-combustion and subsequent calcination in an Ar/H 2 atmosphere at 1250 °C. Photoluminescence properties of the phosphors were thoroughly studied, including excitation, emission, emission color, thermal stability and the process of Ce3+ → Mn2+ energy transfer. The Ba 3 La(PO 4) 3 : x Ce3+, y Mn2+ phosphor series simultaneously exhibited the near-ultraviolet emission of Ce3+ (∼370 nm, 4 f 05 d 1 → 4 f 15 d 0 transition) and the orange-red emission of Mn2+ (∼591–605 nm, 4T 1 → 6A 1 transition) upon exciting the Ce3+ ions with ∼276 nm UV light. Owing to Ce3+ → Mn2+ energy transfer most probably occurring via dipole-dipole interaction, gradually enhanced Mn2+ while weakened Ce3+ emission was resulted at a higher Mn2+ content, with which the emission color can be adjusted from blue through reddish-purple and ultimately to orange red. The efficiency of the energy transfer was analyzed to reach its maximum of ∼43.2% at y = 0.30. It was shown that the Ba 3 La 1- x (PO 4) 3 : x Ce3+ and Ba 3- y La 0.97 (PO 4) 3 :0.03Ce3+, y Mn2+ phosphor series both have favorable thermal stabilities, whose activation energy for thermal quenching of luminescence was calculated to be ∼0.28 ± 0.02 eV for Ce3+ in the former while ∼0.22 ± 0.01 eV for Ce3+ and ∼0.21 ± 0.01 eV for Mn2+ in the latter system. Increasing temperature did not alter the emission wavelength of Ce3+ but gradually blue-shifted that of Mn2+ from ∼602 to 583 nm with increasing temperature from 25 to 200 °C. Graphical abstract Image 1 Highlights • Gel-combustion produced Ce3+ and Ce3+/Mn2+ doped Ba 3 La(PO 4) 3 phosphors. • Photoluminescence properties of the phosphors were thoroughly analyzed. • The mechanism and efficiency of Ce3+.→Mn2+ energy transfer were determined. • Favorable thermal stabilities were demonstrated for the phosphors. [ABSTRACT FROM AUTHOR]

Spherical particles of (Y 1- x Eu x )BO 3 ( x = 0–0.20, ∼0.8–1.5 μm in diameter) have been converted from (Y 1- x Eu x )(B(OH) 4 )CO 3 precursors synthesized via homogenous precipitation processing. Detailed characterizations of the samples were achieved by combined techniques of XRD, Raman, FE-SEM, HR-TEM, PLE/PL, and fluorescence decay analysis. Through homogenous precipitation processing in the absence of EG, orthorhombic (Y,Eu)(B(OH) 4 )CO 3 cubic particles were obtained owing to their crystal habit. Proper EG addition leads to the formation of spherical particles, but nano-sized amorphous particles were resulted from the excessive EG content. Longing reaction time or elevating the reaction temperature induced the appearance of cubic ones. Calcining (Y,Eu)(B(OH) 4 )CO 3 at 700 °C yielded hexagonal structured (Y,Eu)BO 3 phase with the space group of P 6 3 / m , but another hexagonal structured (Y,Eu)BO 3 phase (space group: P 6 3 / mmc ) was obtained with the calcination temperatures of 800–1000 °C. The spherical shape and excellent dispersion of the original particles can be well retained up to 800 °C. Upon UV excitation, the (Y 1- x Eu x )BO 3 ( x = 0–0.20) spheres exhibited a typical Eu 3+ emission with the orange emission at 592 nm from the 5 D 0 - 7 F 1 magnetic dipole transitions of Eu 3+ ions taking the dominant role. Space-group vibrations between in 700 °C-phase and 800–1000 °C phase resulted in the blue shift of CTB center, but they did not significantly affect the lifetimes. A higher Eu content ( x = 0.01–0.10) leaded more Eu 3+ ions occupying the non-centrosymmetric site instead of S 6 one, thus inducing enhanced emission of 5 D 0 → 7 F 2 transition, larger asymmetry factor, and red shift of the CIE chromaticity coordinates. However, the asymmetry factor remains nearly constant with the x value up to 0.20. The fluorescence lifetime is similar (5.3 ± 0.3 ms) up to 8 at% of Eu 3+ , followed by decreases at higher Eu 3+ contents. [ABSTRACT FROM AUTHOR]

Phase-pure (Y 1- x Eu x ) 2 WO 6 ( x = 0.2–0.11) red phosphors (average crystallite size ∼66 nm) in a monoclinic structure have been calcined at 1300 °C from their precursors autoclaved from the mixed solutions of rare-earth nitrate and sodium tungstate dihydrate (Na 2 WO 4 ·2H 2 O) at 180 °C and pH∼10, instead of the commonly adopted pH values of 3–7, without the use of any surfactant. The materials were characterized in detail by the combined techniques of XRD, FT-IR, FE-SEM, TEM, EDS, and optical spectroscopy to reveal (1) the phase structure, morphology, and spatial cation distribution of the hydrothermal product, (2) the course of phase and morphology evolution that leads to the targeted tungstate phosphor, and (3) the effects of Eu 3+ content on photoluminescence properties, including excitation/emission, asymmetry factor of luminescence ( 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 intensity ratio), fluorescence lifetime, and CIE chromaticity coordinates. Through energy transfer from the [WO 6 ] 6− ligands to Eu 3+ , the (Y 1- x Eu x ) 2 WO 6 phosphors exhibit sharp 5 D 0 → 7 F J ( J = 0–4) emissions upon UV excitation into the O 2- -W 6+ charge transfer band peaked at 327 nm, with the red emission at 611 nm being the most prominent ( 5 D 0 → 7 F 2 transition of Eu 3+ ). The optimal Eu 3+ content was determined to be ∼9 at.% ( x = 0.09), and concentration quenching of luminescence was analyzed to be owing to exchange interaction. The emission color moves closer to the red region in the CIE chromaticity diagram with increasing Eu 3+ doping, while fluorescence lifetime of the 611 nm emission, analyzed to be around 1.05 ± 0.05 ms, shows weak dependence on the Eu 3+ content. [ABSTRACT FROM AUTHOR]

[(Gd 0.8 Lu 0.2 ) 0.9− x Tb 0.1 Eu x ] 3 Al 5 O 12 ( x = 0–0.1) garnet phosphors have been calcined from their coprecipitated carbonate precursors at 1300 °C. Detailed materials characterizations are done via XRD, FE-SEM, BET, particle sizing, PL/PLE, and fluorescence decay analyses. The phosphors, with excellent dispersion and uniform particle size and shape, simultaneously exhibit the characteristic Tb 3+ and Eu 3+ emissions with the strongest peaks located at 545 nm (green) and 592 nm (orange red) under the optimal excitation wavelength of 275 nm, which correspond to the 5 D 4 → 7 F 5 and 5 D 0 → 7 F 1 transitions of Tb 3+ and Eu 3+ , respectively. The emission intensities of both Tb 3+ and Eu 3+ remarkably vary with increasing Eu 3+ incorporation, and, as a consequence, the emission color can be readily tuned from approximately green to orange-red. At the optimal Eu 3+ concentration of x = 0.03, the energy transfer efficiency was calculated to be ∼83.2% and the mechanism of energy transfer was analyzed to be electric dipole–dipole interactions. The processes of energy migration among the optically active Gd 3+ , Tb 3+ , and Eu 3+ ions are discussed in detail. Fluorescence decay analysis found rapidly decreasing lifetime for the Tb 3+ emission, conforming to the Tb 3+ → Eu 3+ energy transfer, and the probability of energy transfer is calculated. The [(Gd 0.8 Lu 0.2 ) 0.9− x Tb 0.1 Eu x ] 3 Al 5 O 12 solid-solutions developed in this work may serve as a new type of phosphor that hopefully meets the requirements of various lighting, optical display, and scintillation applications. [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]

Perovskite-type microspheres of LaAlO 3 : x Mn4+, y Ge4+ have been fabricated through thermal decomposition of the amorphous precursors autoclaved from the nitrates and ethylene glycol in the prescence of citric acid. LaAlO 3 : x Mn4+ spheres emit broad and bright near infrared (NIR) emission ranging from 680 nm to 750 nm with the maximum at around 730 nm. The quenching concentration for Mn4+ in LaAlO 3 is found at x = 0.1%. In the absence of light source, the spheres emit intense NIR afterglow for 10 min at room temperature, mainly due to the formation of [Mn Al defects. Doping Ge4+ does not significantly change the morphology, crystal structure, band gap, and thermal stability of LaAlO 3 :Mn4+ sample, but it induces stronger asymmetry of MnO 6 and more isolated Mn4+ ions, which thus contributes to greatly enhanced NIR emission intensity by 260%. Ge4+ ions occupying Al site leads to the formation of positive [Ge Al defects, which are closely related to the trap concentration rather than the trap depth. Incorporation of Ge4+ gives rise to the improved persistent luminescence, and the most intense afterglow is found at y = 0.6%. The spheres exhibit repeatable afterglow by a proper heat processing in the absence of light source, indicating their potential application in optical data storage. Image 1 • Perovskite-type microspheres of LaAlO 3 :Mn4+/Ge4+ were originally synthesized. • Doping Ge4+induced a greatly enhanced NIR emission intensity by 260%. • Incorporation of Ge4+ gave rise to the improved persistent luminescence. • The spheres exhibited repeated illumination by heating without light source. [ABSTRACT FROM AUTHOR]