The Research On Spectral Modulation And Energy Transfer Of Rare-earth Doped Down Conversion Luminescent Material

With the increasing of global energy shortage and environmental problem, solar energy which is renewable and green attracts a widespread attention. Crystalline silicon ?c-Si? solar cells occupy the main commercial market, which have important applications in many fields, such as the aerospace, industry, agriculture, military and civilian. However, the photoelectric conversion efficiency is low due to the spectral mismatch between sunlight spectrum ?300?2500 run, AM 1.5G? and the response curve of c-Si semiconductor ???1100 nm?. Hence, enhancing the photoelectric conversion efficiency of silicon solar cell by spectral modulation has become one of the hottest topics in academic and industrial society. Given this, the absorbed solar light ?300?500 nm? could be convert to near infrared ?NIR? ?900?1100 nm? and visible light via energy transfer ?ET? process, which could reduce energy loss and enhance the conversion efficiency of silicon solar cell. In this paper, molybdates, chlorine borates, borates, vanadates were selected as the hosts and RE³⁺ ions (eg. Ce³⁺, Pr³⁺, Yb³⁺) as the dopants. Rare-earth ?RE? ions doped down-conversion ?DC? luminescent materials for c-si solar cells were synthesised by sol-gel and solid state reactions. The main work and contributions of the dissertation are as follows:Li₈Bi₂?MoO₄?₇:RE³⁺ and Li₈Bi₂?MoO₄?₇:RE³⁺, Yb³⁺?RE= Dy, Tb, Pr? phosphors were prepared by sol-gel reaction. Dy³⁺ ion and Dy³⁺-Yb³⁺?Pr³⁺-Yb³⁺ and Tb³⁺-Yb³⁺ were acted as dopants. The synthesis condition, structure and phase, doping concentration, DC luminescent property were investigated via X-ray diffraction and fluorescence spectrometer. The proportion of yellow/blue emission intensity in Li₈Bi₂?MoO₄?₇:Dy³⁺ host have been determined, and white light emission was sucessfully obtained. The energy transfer efficiency in Dy³⁺-Yb³⁺?Pr³⁺-Yb³⁺?Tb³⁺-Yb³⁺ phosphors was calculated and DC energy transfer mechanism was analyzed. The dependence of Yb³⁺ NIR emission intensity on Dy³⁺ /Pr³⁺/Tb³⁺ narrow-band ?f-f? sensitizer and the potential of Li₈Bi₂?MoO₄?₇:Dy³⁺/Pr³⁺/ Tb³⁺-Yb³⁺phosphor in silicon-based solar cells were investigated.RE³⁺-Yb³⁺?RE= Tb, Pr, Nd?, Ce³⁺/Tb³⁺-Yb³⁺ co-doped and Ce³⁺-Tb³⁺-Yb³⁺tri-doped Ba₂Y?BO3?2Cl samples were prepared via conventional solid-state reaction. The ET process from Tb³⁺/Pr³⁺/Nd³⁺ to Yb³⁺ in co-doped stystem were studied. The DC luminescent properties of optimal tri-doped and corresponding Ce³⁺/Tb³⁺-Yb³⁺ co-doped phosphors were compared. The ET mechanism and possible four DC processes Ce³⁺? Tb³⁺, Ce³⁺?Yb³⁺, Tb³⁺?Yb³⁺a nd Ce³⁺?Tb³⁺?Yb³⁺in Ce³⁺-Tb³⁺-Yb³⁺ tri-doped phosphor were proposed. The bridge role of Tb³⁺ in ET process was stated, and Ce³⁺ ion with f?d transition is an efficient sensitizer, which enormously enlarges the absorption cross-section in the UV-vis region and enhances the NIR emission of Yb³⁺ ions. This manifests Ba₂Y?BO3?2Cl:Ce³⁺, Tb³⁺, Yb³⁺phosphor is a promising DC spectral convertor for c-si solar cells.Ba₃Y?BO₃?₃:Ce³⁺, Nd³⁺ NIR DC phosphors were synthesized by solid-state reaction, which could convert UV-Vis to NIR emission via the ET process from Ce³⁺to Nd³⁺. The samples offer characteristic blue-violet wide emission spectrum of Ce³⁺and give an intense NIR emission of Nd³⁺. The effect of Nd³⁺ ions doping concentration on the NIR intensity was discussed. This reveals that Ce³⁺-Nd³⁺ co-doped Ba₃Y?BO₃?₃ DC phosphor could emit NIR emission in 900-1100 nm and enhance the conversion efficiency of silicon-based solar cells.Rare earth doped Ba₂RV₃O₁₁?R= La, Y, Gd, Bi? vanadate host were synthesized via sol-gel method. The DC properties of Ba₂R1-xEuxV₃O₁₁ ?R= La, Y, Gd, Bi? were analyzed. The luminescent properties and ET mechanism in the host-sensitized Ba₂LaV₃O₁₁:Yb³⁺ and Ba₂YV₃O₁₁:Nd³⁺/Ho³⁺/Yb³⁺ NIR DC phosphors were emphatically studied. The ET process from [VO4]3- group to the doping RE³⁺ ions was confirmed and the ET mode in Ba₂LaV₃O₁₁:Yb³⁺ was explored. These phosphors are promissing DC spectrum modulation materials for c-Si solar cells.