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Understanding site-selective fluorescence is one of valuable importance for spectrum modulation. In this Letter, we observed the existence of two non-equivalent Gd-activated crystallographic sites in an Er3+-doped hexagonal Na1.5Gd1.5F6 phosphor. It is proved that two green emissions from the S3/24 level separately originate from the Gd1 (540 nm) and Na2/Gd2 (550–555 nm) crystallographic sites, and the 657 nm red emission from the F9/24 level only originates from Na2/Gd2 site through using the time-resolved luminescence spectra. The 142.2% absolute enhancement of the red emission is realized through the synergistic effect of ultraviolet downconversion and infrared upconversion induced by the 370 nm and 1.54 μm dual-mode excitation.

Density functional theory simulation with a U correction (DFT + U) was adopted to predict the proper experimental conditions required to generate divalent europium (Eu2+) in α-Al2O3 host material consolidated via vacuum consolidation. Accordingly, samples of 0.1 at% Eu2+:α-Al2O3 were obtained by gelcasting, followed by high vacuum sintering process (

The novel long persistent luminescence phosphors MAl2O4:Yb2+ (M = Ba, Sr) have been synthesized by a solid-state reaction. BaAl2O4:Yb2+ exhibits intense blue luminescence emission and the persistent time is even longer than the commercial phosphor SrAl2O4:Eu2+, Dy3+. The incorporation of Dy3+ ion as trap center evidently enhances persistent time of Yb2+ in SrAl2O4:Yb2+ host. We believe that MAl2O4:Yb2+ would replace the commercial SrAl2O4:Eu2+ as a new generation of long persistent luminescence materials due to the cheaper Yb2O3 than Eu2O3. To investigate the application in solar cell, MAl2O4:Yb2+ (M = Ba, Sr) phosphors are doped into methyl methacrylate monomer (MMA) polymer. The short circuit current density (Isc) of solar cell containing BaAl2O4:Yb2+ can easily be measured after removing the irradiation source.

The optical properties of CuAlO2:Y3+ electrospun nanofibers have been studied through UV-VIS transmittance/reflectance and photoluminescence. A blueshift of the PL spectra was identified for the samples with decreased crystallite sizes and increased doping levels. Analysis of the samples with a quantum size model showed discrepancies resulting from the Y3+ doping, indicating a further band-gap enhancement due to the change in hybridization between the 3dz2 and 4s orbitals in the CuMO2 delafossite. The comparative investigation between size effect estimation and the nominal band-gap enhancement could benefit future research on trivalent doping and violet emission tuning.

Eu-doped fluorosilicate apatites M2Y3[SiO4]3F (M = Sr, Ba) are prepared by solid state reaction. Unlike conventional Eu-doped materials, coexistence of Eu3+ and Eu2+ ions is found from the photoluminescence of Eu-doped apatites M2Y3[SiO4]3F (M = Sr, Ba) which were prepared in reducing atmosphere. Eu2+ ions are converted from Eu3+ ions in the reduction process. It is suggested that Eu2+ ions occupy A(I) (4f) or A(II) (6h) crystallographic site in the apatite lattices. Intense emission lines due to Eu3+ are observed at 600-630 nm, while broad emission band due to Eu2+ is observed at 450-650 nm. These emissions combined with blue emission from LED are suitable to obtain white light, i.e., white LEDs for lighting and display. Different luminescence characteristics are obtained between Sr2Y3[SiO4]3F:Eu and Ba2Y3[SiO4]3F:Eu, which were prepared in reducing atmosphere.

Eu3+-doped NaLa4Mo3O15F was prepared by solid-state method and characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The luminescence properties such as the excitation and emission spectra, the internal quantum efficiency (QE) and the thermal stability were investigated. The optimal level of Eu3+-doping was determined by the luminescence intensities and QEs. The phosphor exhibits a bright red luminescence at 615 nm corresponding to the electric dipole transition 5D0→7F2, which is more efficient than the commercial phosphor of Y2O2S:Eu3+. With the increase of Eu3+-doping the charge transfer band (CTB) shows an obvious red-shift, which presents a longer wavelength than any other reported Eu3+-doped molydates with non-cubic structures. NaLa4Mo3O15F:Eu3+ has excellent properties such as the high quantum efficiency excited in near-UV and blue wavelength, the high thermal stability, etc. This is benefited from its structural characteristics: the cubic crystalline phase with MoO6 groups and the incorporation of F- ions in the host lattices.

The self-activated yellow-emitting phosphors of vanadates Ca5M4(VO4)6 (M = Mg, Zn) were synthesized via the solid-state reaction route. The formation of single phase compound with garnet structure was verified through X-ray diffraction (XRD) studies. The excitation and emission spectra and the thermal quenching of luminescence intensities were measured. The different luminescence properties of Ca5Mg4(VO4)6 and Ca5Zn4(VO4)6 phosphors were presented, e.g., the spectra shift, the luminescence lifetimes, the absolute quantum efficiency, the color coordinates and the Stokes shift. This deference was discussed on the base of the relationship between the micro-structure and the charge transfer transitions in [VO4]3- groups in the lattices. Ca5Mg4(VO4)6 could be suggested to be a potential yellow-emitting phosphor for the application on near-UV excited white LEDs.

The single-phased K(2)Y(1-x)Eu(x)Zr(PO(4))(3) (x=0~1) phosphors were prepared by solid-state reaction. The greenish-blue Zr(4+)-emission due to the Zr(4+)-O(2-) charge transfer transition is observed in the K(2)YZr(PO(4))(3) (x=0) phosphor under UV excitation. Together with the Zr(4+)-emission, the red emission of Eu(3+) is progressively developed by replacement of Y(3+) to Eu(3+) over the full Eu-content (x=0~1) in K(2)Y(1-x)Eu(x)Zr(PO(4))(3). The emission color varies from greenish-blue to whitish with increasing Eu(3+)-content and the white-light emission is realized in single-phased phosphor of K(2)EuZr(PO(4))(3) (x=1) by combining the Zr(4+)-emission and the Eu(3+)-emission.

The radiative emission properties of the Dy3+ ions in an oxyfluoride glass and glass-ceramics have been studied for the generation of white light. The x-ray diffraction pattern of the glass-ceramics shows the formation of CaF2 fluorite-type nanocrystals in the glass matrix after a suitable thermal treatment of the precursor glass, whereas time-resolved optical measurements show the incorporation of the Dy3+ ions in the CaF2 nanocrystals. Intense white light has been observed when the samples are excited with 451 nm laser light. From the visible emission spectra, yellow to blue intensity ratios and the chromaticity color coordinates have been determined. All the color coordinates are found to lie in the white light region of the chromaticity color diagram.

Metaphosphate glasses doped with five concentrations of Er3+ ions have been investigated through absorption and emission spectra, decay curves, and upconversion measurements. Judd-Ofelt parameters have been evaluated from absorption spectrum of the 1.0mol.%Er3+-doped glass, which are in turn used to predict radiative properties of some important luminescence levels of Er3+ ions in these glasses. Gain bandwidths of an optical amplifier have been evaluated and are compared with those of reported Er3+:glass systems. Temperature dependence of the 1.5μm emission has been studied for the 2.0mol.%Er3+-doped glass from 13K to room temperature. Lifetimes of the I13/24 level were measured and are found to decrease with concentration of Er3+ ions after 0.1mol.%. Concentration quenching of lifetimes has been analyzed using the theory developed by Auzel [J. Lumin.94-95, 293 (2001); Opt. Mater.24, 103 (2003)]. Infrared to visible upconversion was also measured for three concentrations of Er3+-doped metaphosphate glasses with 794nm excitation. A mechanism, involving excited state absorption and energy transfer upconversion, has been proposed to explain the upconversion process.

We investigated energy-transfer processes associated with clustered sites of Er3+ ions in LiNbO3 crystals leading to upconverted blue-green fluorescence and cross relaxation with the analyses of fluorescence transients measured by site-selective excitations. We found two clustered sites with distinct lifetimes of 3 and 16 μs at room temperature for the green fluorescing levels (4S3/2), which were much shorter than the lifetimes of isolated sites (27 μs) that are due to nonradiative energy-transfer processes. The green upconverted fluorescence originates from the energy transfer of one clustered site in the 4I7/2 levels, and/or of the other clustered site in the 4I11/2 levels. Our analyses verified that the fluorescence efficiencies of Er3+ ions in the clustered sites are significantly decreased because of their interionic nonradiative energy transfers. Therefore, the formation of clustered sites in Er3+-doped LiNbO3 crystals gives rise to deleterious effects on laser and amplifier applications.