We report the observation of enhanced red emission at 613 nm originating from 5 D 0 f 7 F 2 transition of Eu 3+ -doped CaMoO 4 with Bi 3+ as an additive, under excitation either into the 5 L 6 state with 395 nm or the 5 D 2 state with 465 nm. The luminescence properties as a function of Bi 3+ and Eu 3+ concentrations are studied. Strongly enhanced red emission of Eu 3+ is obtained by adding Bi 3+ instead of increasing the Eu 3+ concentration. For a fixed Eu 3+ concentration, there is an optimal Bi 3+ concentration, at which the maximum luminescence intensity is achieved. The red emission of CaMoO 4 :0.05Eu 3+ is enhanced by a factor of 3 as 0.2 Bi 3+ is co-doped into the system, stronger than that of commercial Y 2 O 2 S:Eu 3+ and Y 2 O 3 :Eu 3+ phosphors. Lifetime and diffuse reflection spectra measurements indicate that the red emission enhancement is due to the enhanced transition probabilities from the ground state to 5 L 6 and 5 D 2 states of Eu 3+ in the distorted crystal field in which it is considered that more odd-rank crystal field components are induced by crystal structural distortion and symmetry decreasing with the addition of Bi 3+ , leading to more opposite parity components, for example, 4f 5 5d states, mixed into the 4f 6 transitional levels of Eu 3+ . The energy transfer from Bi 3+ to Eu 3+ also occurs and is discussed. The present material is a promising red-emitting phosphor for white light diodes with near-UV/blue GaN-based chips.

This work reports a simple hydrothermal route using citric acid as a "shape modifier" for the controlled synthesis of luminescent TbPO 4 :Eu nanocrystals. The size and morphology of products change remarkably when the proportion of citric acid involved in the reaction increases. The multiple roles that citric acid plays during the controlled synthesis are discussed to try to understand the crystallization and growth dynamics of TbPO 4 crystals. The photoluminescence properties of TbPO 4 :Eu are investigated. The excitation spectra and the variation of the 5 D 4 lifetime values as a function of the Eu 3+ concentration points out the occurrence of Tb 3+ -to-Eu 3+ energy transfer, resulting in a maximum absolute emission quantum yield of 0.14. The possibility to tune the size, the shape, and the optical properties of the nanocrystals reported in this work might be useful for applications in optoelectronics or biolabeling. Moreover, this simple approach might also be applied for the synthesis of other luminescent phosphates.

ZnWO4:Eu3+ nanocrystals were prepared by the hydrothermal method at various temperatures and pH values. Their luminescent properties including excitation and emission processes, luminescent dynamics, and local environments surrounding Eu3+ ions were systemically studied. The results indicate that the particle size of the nanocrystals grows with increasing hydrothermal temperature, while it rarely changes with pH value. The excitation bands for Eu3+, which are contributed by different components, shift considerably to blue with the increasing pH value. The relative intensity of blue-green emission bands caused by the tungstate groups can be greatly modified by changing the pH value, thus the white color phosphors can be obtained. There exist two symmetry sites for the 5D0−7F2 emissions of Eu3+, inner and surface. The former corresponds to lines with narrower inhomogeneous width and slower decay time, while the latter to the lines with broader width and faster decay time. The emissions for tungstate groups mainly originate from the charge transfer from excited 2p orbits of O2- to the empty orbits of the central W6+ ions. On the other hand, the emissions for Eu3+ ions are contributed by both the charge transfer from O2- to Eu3+ and the energy transfer from W6+ ions to Eu3+ ions. A schematic is proposed to explain the photoluminescence processes in the ZnWO4:Eu3+ nanocrystals.

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The synthesis and upconversion luminescence properties upon a 980 nm pump of cubic Lu 1.88 Yb 0.1 Er 0.02 O 3 nanocrystals with various shapes, e.g., nanorods, nanosheets, and nanoparticles, are studied. It is observed that with decreasing size of the nanocrystals, the relative intensity of the upconverted red emission (Er 3+ : 4 F 9/2 f 4 I 15/2 ) to the green one (Er 3+ : ( 2 H 11/2 , 4 S 3/2 ) f 4 I 15/2 ) is increased, and a three-photon process involved in the green upconversion, as described by 4 F 9/2 (Er) + 2 F 5/2 (Yb) f 2 H 9/2 (Er) + 2 F 7/2 (Yb), is synchronously enhanced. An analysis based on steady-state rate equations indicates that the results can be induced by a large 4 I 11/2 f 4 I 13/2 nonradiative relaxation rate with a small 4 F 9/2 f 4 I 9/2 nonradiative relaxation rate. The large 4 I 11/2 f 4 I 13/2 nonradiative relaxation rate is attributed to the occurrence of efficient cross energy transfer to OHsurface group due to the good energy match. As the size of the nanocrystals decreases, the relative surface area is increased, increasing the number of OHgroup that can attach to the surface, therefore, enhancing the 4 I 11/2 f 4 I 13/2 nonradiative relaxation rate through cross energy transfer to OHsurface group.

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The red photoluminescence and phosphorescence originating from D21-H43 transition of Pr3+ in CaTiO3 nanoparticles are studied as a function of Pr3+ concentrations. The nanophosphors exhibit both longer persistence time of 30min and higher quenching concentration of 0.4mol% than the bulk (10min and 0.1mol%). The initial phosphorescence in the nanophosphor is an order of magnitude stronger than that in the bulk at the corresponding quenching concentrations. Phosphorescence decay patterns and diffused reflectance spectra before and after ultraviolet exposure indicate the existence of more traps contributing to phosphorescence in the nanoparticles.