Reduction, Luminescence Spectra And Stability Of Divalent Samarium Ions

There has been much interest in research of Sm2+doped materials since persistent spectral hole burning (PSHB) at room temperature (RT) was reported in Sm2+doped inorganic material. Sm ions are stable in the trivalent state in many host materials. So it is necessary to reduce the Sm3+ions to Sm2+ions before the application of luminescence Sm2+ions is explored.Usually, a strong reducing atmosphere is required for the reduction of Sm3+to Sm2+ions. It needs a rather complicated gas flow system that is difficult to perform. Another well-known reduction method is to irradiate samples with high energy radiation, such as femto-second (fs) laser, β-rays, y-rays, and X-rays.To compare the luminescece properties and stabilities of Sm2+ions under two different reduction methods, we could find a better reducing process for PSHB material.Sm2+ions are also good probe materials. They are highly affected by their surrounding environment in the lattice. If there is a tiny difference in crystal structure, we will find a different5D0→7F0transition from the selective excitation and emission spectra which also has a different decay curve. With advantage of this feature, we can study the surrounding environment of ions and detect symmetry of rare-earth ions in the material which provides the symmetry of different luminescence centers in the matrix and then gives details of physical structures.This paper used LiBaB9O15, Ba3BP3O12, Ba2Si04and SrO-BaO-P2O5-B2O3glass as substrate materials, Sm2+as activating ions. Sm2+ions doped LiBaBgO15, Ba3BP3O12, Ba2Si04and SrO-BaO-P2O5-B2O3glass were prepared by high temperature solid-state reaction and high-temperature melt quenching method, separately. Sm2+ions were reduced by X-ray irradiation and reducing atmosphere. The main topic in this work is to realize reproduction and reduction mechanism of Sm2+by X-ray radiation and reducing atmosphere, the luminescence spectra, decay curves were measured for the Sm2+ions. The microstructure of materials were also discussed.In the chapter three, Sm2O3-doped SrO-BaO-P2O5-B2O3glass was prepared by a conventional melt quenching method in the air. The glass was irradiated with X-rays to reduce the Sm3+ions to Sm2+ions. After the X-ray irradiation, photoluminescence studies at different temperatures showed that the conversion of Sm3+to Sm2+could be realized in this alkaline-earth borophosphate glass. The luminescence of the Sm2+ions showed a strong dependence on temperature. Photo-stability of Sm2+ion was evaluated by a photo-bleaching method. Thermo-luminescence and life-time measurements were also investigated. The results of this study could be useful for understanding the reduction mechanism of Sm3+ions to Sm2+ions in alkaline-earth borophosphate glass.In the chapter four, Sm3+-doped Ba2SiO4phosphor was prepared by high-temperature solid-state reaction. The reduction of Sm3+to Sm2+was achieved by X-ray irradiation on the as-prepared Ba2SiO4:Sm3+. With the increasing exposure time, the Sm2+-luminescence tends to be stronger up to10h and then saturated. The Sm2+ions with different site symmetries formed in Ba2SiO4were observed in the emission spectra due to the5D0→7F0transition and the decay curves of the5D0level at various temperatures (10-300K). The Sm2+at the different sites in Ba2SiO4showed different quenching temperatures. Three crystallographic sites were identified in Ba2SiO4below150K. However, only one site was left at temperature higher than190K. The mechanism involved in the conversion of Sm3+to Sm2+under X-ray irradiation was discussed on the base of the crystal structure, crystallographic site-distributions, charge compensations, the crystal field strength acting on Sm2+, and the defects created by X-ray irradiation. The photo-stability of the Sm2+was evaluated with the photo-bleaching.In the chapter five, Sm3+-doped LiBaBgO15polycrystalline sample was prepared by the conventional solid-state reaction. X-ray irradiation could cause Sm3+→Sm2+conversion in this host. The luminescence spectra and decay curves of the Sm2+ions were investigated. The thermal-stability of the Sm2+ions generated by X-ray irradiation was investigated by taking the luminescence spectra after heat treatment at different temperatures in air. The photo-stability of the Sm2+ions was evaluated by photo-bleaching method. The results showed that the Sm2+ions in LiBaB9O15created by X-ray irradiation had higher stability than the reported references.In the chapter six, Sm2+ions doped in Ba3BP3O12polycrystalline samples were obtained by heating the materials in a reducing atmosphere and X-ray irradiation reduction method. The temperature dependent emission spectra and luminescence decay curves of Sm2+ions reduced by the two methods were investigated at various temperatures (10-300K). The crystallographic site distributions and the thermal-quenching of5D0→7F0luminescence transition of Sm2+ions in the two samples have different characteristics. The photo-stabilities of the Sm2+ions were evaluated with the photo-bleaching method. The luminescence and reduction mechanism of Sm3→Sm2+were discussed.This paper, the photoluminescence performances and Stability of Sm2+ions doped in LiBaB9O15, Ba3BP3O12, Ba2Si04and SrO-BaO-P2O5-B2O3glass were systematically studied. The reduction mechanism of Sm3+ions to Sm2+ions by X-ray irradiation in Ba2Si4and SrO-BaO-P2O5-B2O3glass was firstly investigated. The differences between reducing atmosphere and X-ray irradiation reduction methods in Sm2+ions doped in Ba3BP3O12were also firstly investigated. The results in this paper give some necessary information for its possible applications for optical storage devices.