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[Display omitted] • Y 2 Mo 4 O 15 : x Yb3+/ y Ho3+ UC phosphors were converted from a new type of precursor. • The process of phase and morphology evolution was unveiled. • Y 2 Mo 4 O 15 : x Yb3+/ y Ho3+ exhibits strong deep-red (630–670 nm) emission under 978 nm laser pumping. • The optimal contents of Yb3+ and Ho3+ were determined. • The photon process of UC luminescence was explained in detail. Hydrothermal reaction of Y(NO 3) 3 ·6H 2 O and (NH 4) 6 Mo 7 O 24 ·4H 2 O at 180 °C for 24 h was performed in this work via systematically varying the solution pH (4–10) and Mo/Y molar ratio (R, 2–5), which produced a NH 4 Y(MoO 4) 2 ·0.19H 2 O new compound that yielded phase-pure Y 2 Mo 4 O 15 upon calcination at 500–700 °C. The pH/R window for the compound to crystallize was determined to be 6–7/3 and 6–9/4–5. The products were characterized in detail by XRD, FTIR, elemental analysis, SEM, TEM, STEM and TG to understand chemical composition and the courses of phase/morphology evolution. Applying the above synthesis strategy successfully produced Y 2 Mo 4 O 15 : x Yb3+, y Ho3+ phosphors that exhibit strong deep-red (630–670 nm, 5F 5 → 5I 8 transition) and weak green (530–560 nm, 5F 4 /5S 2 → 5I 8) emissions under 978 nm laser pumping, where the optimal Yb3+ and Ho3+ contents were determined to be x = 0.20 for y = 0.01 and y = 0.03 for x = 0.10, respectively. Spectral analysis indicated that the up-conversion luminescence occurred via a two-photon process, with the red/green intensity ratio and also the emission color dependent on Yb3+ and Ho3+ contents, which were explained by considering ground state excitation, energy transfer, non-radiative relaxation and cross relaxation. [ABSTRACT FROM AUTHOR]

A series of well-dispersed (Ce 1- x Tb x)PO 4 (x = 0–1) microspheres, with an average diameter of ∼1.2 μm, have been originally prepared via two-phase interfacial precipitation and subsequent calcination. Characteristics of the as-synthesized and calcination products were investigated by the combined techniques of XRD, FE-SEM, TEM, FT-IR and TG-DSC. Under 275 nm excitation, tuning the emission color from blue (0.17, 0.02) to green (0.30, 0.56) was realized via varying the Tb3+ content and through Ce3+ → Tb3+ energy transfer. The optimal content of Tb3+ was found to be ∼15 at% (x = 0.15), and the energy transfer was determined to occur via electric dipole-dipole interaction. Moreover, both the emissions of Ce3+ and Tb3+ present gradually higher thermal stability with increasing Tb3+ content owing to enhanced energy transfer. The (Ce 0.85 Tb 0.15)PO 4 microspheres, which possess the highest absolute quantum efficiency (∼60.1%) across the series and excellent thermal stability (activation energy for thermal quenching of luminescence: ∼0.312 eV), may potentially serve as a single-phase green phosphor for solid-state lighting and field-emission display. Multi-color luminescent (Ce 1- x Tb x)PO 4 (x = 0–1) microspheres were successfully fabricated via gel/solution interfacial precipitation and subsequent calcination. Image 1 • (Ce 1- x Tb x)PO 4 (x = 0–1) microspheres were obtained via interfacial precipitation. • The formation mechanism of (Ce 1- x Tb x)PO 4 spheres was proposed. • Ce3+.→ Tb3+ energy transfer was analyzed to occur via dipole-dipole interaction • (Ce 0.85 Tb 0.15)PO 4 has favorable thermal stability for Tb3+ luminescence. [ABSTRACT FROM AUTHOR]

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]

[(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]

Abstract: This paper reports the synthesis and luminescence properties of rare earth doped BiPO4:Ce,Tb nanorods which were prepared via a solvothermal method. The nanorods are of hexagonal structure and they have intense luminescence. In Ce3+/Tb3+ co-doped nanorods, there is energy transfer from Ce3+ to Tb3+ which enhances the luminescence of Tb3+. These materials may find applications in solid state lighting and radiation detection. [Copyright &y& Elsevier]

• 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]