Synthesis And Luminescence Properties Of Molybdates And Tungstates

At present, for solar cells, the effective utilization of solar energy is still very low which inhibited the widely use of solar cells. Moreover, ultraviolet or near-ultraviolet light will reduce the life of the solar cells. Therefore, in order to improve the efficiency of photovoltaic solar cells and extend solar cells life, it is very necessary to turn the harmful ultraviolet and near-ultraviolet light into the visible light region especially the red light region which can be efficiently absorbed by solar cells. Based on the crystal structure and sites information, we designed the type of sensitizer and rare-earth doped phosphors. Prepare conditions and alkali metal ions were investigated to improve the luminescence intensity. Synthesizing the highly efficient fluorescent materials is very important for solar cells so as to achieve the purpose of increasing the efficiency of solar cells.(1) Preparation and fluorescence properties of ZnWO4:Bi3+, Sm3+ phosphors. Firstly, Sm3+ ions which have red emitting lights were introduced into the zinc tungstate (ZnWO4) hosts. Using the lowe excitation bands position of Bi3+ions in ZnWO4 host, the range of excitation bands were broadended. The Li+ions were added to adjust the charge balance. And the luminescence intensity was enhanced more than three times. According to the lattice environmental information, we detailly investigated the relationship between occupation sites and energy transmission.(2) Preparation and fluorescence properties of CdWO4:Bi3+, Sm3+phosphors. We introduced Bi3+ions to sensitize Sm3+ions which have red emitting lights into the cadmium tungstate (CdWO4) hosts to lower the excitation energy and improve the red emission intensity of the fluorescent materials,. The crystal structures, band structures and self-activation fluorescence properties were studied in detail. We analyzed the position of Bi3+ion 1So-3Pi energy and energy transfer mechanism from Bi3+to Sm3+ions. Compared with the crystal structure of zinc tungstate (ZnWO4) we found that the energy transmission from Bi3+to Sm3+ions is closely related to the crystal structure of the undee single line structure.(3) Preparation and fluorescence properties of ZnMoO4:Bi3+, Eu3+phosphors. We detailly investigated the ZnMoO4:Eu3+, Bi3+red phosphors. And we found the distinctive S-shaped cluster structure of Zn-O polyhedron in ZnMoO4 host. According to the characteristics of ZnMoO4 crystal structure we identified the occupation positions of Bi3+, Eu3+and alkali metal ions. And we proposed a method to increase the fluorescence intensity of phosphors using crystal sites. The optimized fluorescent materials' excitation bands were located near ultraviolet region of the spectrum and the fluorescence intensity was higher than the commercial Y2O3:Eu3+ and Sr2Si5N8:Eu2+ red fluorescent materials. It is a potential fluorescent conversion material for solar cells.(4) Preparation and fluorescence properties of MgMoO4:Bi3+, Eu3+phosphors. We synthesized a series of Mg1-x-yMoO4:xEu3+, yBi3+fluorescent materials via a high temperature solid-state reaction method. The impacts of sintering temperatures on emission intensity of the materials were investigated. The optimal doping concentration of Eu3+and Bi3+ions were related to the Mg-O cruciform cluster structures. The introduction of charge compensation agents can significantly improve the luminescence intensitys.(5) Preparation and fluorescence properties of CdMoO4:Bi3+, Eu3+phosphors. We prepared a series of CdMoO4:Bi3+, Eu3+red phosphors via high temperature solid state reaction method. The experiment parameters were further optimized to determine the optimum doping concentration of Eu3+. Based on this we co-doped Bi3+ions into CdMo04:Eu3+red phosphors and investigated the impact on phase structure and luminescence properties. The influences of the charge compensators on fluorescent luminescence properties were also investigated. The obtained fluorescent materials are potential fluorescent conversion material for solar cells because the excitation bands were located at near ultraviolet region and the luminescence intensity was very high.