Eu-doped pollucite CsAlSi2O6 was synthesized by the sol-gel method and heated in an air atmosphere. The crystal structure and the microstructure of the phosphors were investigated by X-ray powder diffraction and SEM images, respectively. The photoluminescence spectra and temperature dependent decay curves were measured. An abnormal reduction phenomenon of Eu(3+) → Eu(2+) was reported when Eu(3+) ions were doped in alkaline metal cation sites in CsAlSi2O6 prepared in an oxidizing atmosphere. The abnormal mechanism was discussed on the basis of the charge compensation model and a rigid three-dimensional framework structure of CsAlSi2O6. The luminescence color centers were investigated by luminescence decay lifetimes and thermal stabilities of Eu(2+) ions. The defect complexes of [(Eu(3+)Cs)(••)-2VCs'] or [(Eu(3+)Cs)(••)-Oi″] induced by the substitution of Eu(3+) on Cs(+) were suggested in the lattices. Eu(2+) ions could be regarded as Eu(3+) ions combining with the released electrons from defects Oi″ or VCs' in close vicinity of Eu(3+) (Eu(3+) + e); the electrons cannot enter the atom track of Eu(2+) presenting luminescence of Eu(2+) ions. The results indicate that several defect traps can be attributed to the abnormal reduction mechanism of Eu(3+) to Eu(2+) ions in a matrix.

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The Sm2+ -doped SrZn2(PO4)2 phosphor was prepared by the high temperature solid-state reaction method. The temperature-dependent emission spectra and luminescence decay of Sm2+ ions were investigated from 10 to 300 K. The investigation was focused on the site distributions of Sm2+ ions in this host, which exhibited different spectroscopic features at varying temperatures. Two crystallography sites existed for Sm2+ ions in this host below 170 K, where no energy transfer could be detected between them. However, only one Sm2+ site was left from 170 K to room temperature. The photostability of the Sm2+ ion was evaluated by the photobleaching method. This investigation would be helpful for understanding the doping mechanism and applications of rare-earth ions doped in this phosphate host.

BiVO4 was selected as a model to manipulate the luminescence and photocatalysis by Eu3+ ions incorporation. Eu3+-uniformly doped and surface-localized BiVO4 was prepared by a coprecipitation route and cation exchanges, respectively. The phase-formations, surface characteristics, and band structures were measured. A comparative study of photoenergy conversion activities, that is, photocatalysis and photoluminescence, was conducted. Eu3+-surface-localizing on BiVO4 improves both visible light harvest and photodegradation on RhB dye, while, Eu3+-uniformly doping deteriorates the photocatalysis of BiVO4. In Eu3+-uniformly doped BiVO4 nanoparticles, 5D0 → 7F0,1,2,3,4 luminescence quenched in the monoclinic phase, whereas it could be observed in the tetragonal formation. Differently, Eu3+-surface-localized BiVO4 with the monoclinic formation showed both enhanced Eu3+ luminescence and improved photocatalysis. A band model was proposed to discuss the luminescence mechanism. Bi 6s levels could contribute different energy positions in band structures of monoclinic and tetragonal phases, which play a vital role in the photoenergy conversion. Eu3+ ions incorporated in BiVO4 could be used to study multimodal photoenergy models such as photocatalysis and photoluminescence.