The Research On Rare Earth Ions Doped Near Infrared Down-conversion Luminescent Materials

Due to the energy crisis and environmental pollution caused by traditional energy sources has become increasingly serious, the solar energy, as the clean and renewable energy, has received widespread attention. But at present,the conversion efficiency of silicon-based solar cells, which is most widely used in photovoltaic system is generally low. The reason is that the mismatch between solar spectrum and the spectral response of solar cells cause a lot of energy loss in the process of converting solar energy into electric energy. Spectral modification of sunlight can improve the energy transfer efficiency of solar cells effectively. Moreover, down-conversion, a way of spectral modification, can transfer an ultraviolet photon or a visible photon into near-infrared photons which match well with the band gap of silicon solar cells. Thus, the research of down-conversion materials is popular in recent years.Three new down-conversion luminescent materials were prepared by high temperature solid state reaction in this thesis, and their down-conversion progress were investigated as well. Firstly, Ca₂V₂O₇ was used as matrix, Yb³⁺ ion was singly doped with different concentration, the down-conversion luminescence properties were discussed. When excited by 358 nm, a broad emission band centered at 650 nm is observed, which is assigned to the emission of VO₄^3-. Meanwhile, one broad emission band centered at 976 nm aroused by the transition of Yb³⁺:²F_5/2?²F_7/2 is observed. When monitored at 976 nm, the detected excitation band ranged from 250 nm to 500 nm is consists of the Yb-O charge transfer band and a O-V charge transfer band, indicating that two energy transfer routines existed in this system. When the Yb³⁺ doped concentration varies from 1% to 9%, the quantum efficiency under the excitation of 358 nm increased from 103.5% to 127.8%.In the second part, the near infrared quantum cutting process in Sr MoO₄ doped by Yb³⁺ ions was discussed. A broad emission band centered at 493 nm aroused by Mo O42-and a near-infrared emission around about 1000 nm which is originated from the transition of Yb³⁺:²F_5/2?²F_7/2 can be excited by 290 nm. Meanwhile, the emission intensity of the matrix decreased with the Yb³⁺ doped concentration increased, which verified the existence of energy transfer between MoO₄^2- and Yb³⁺. When the doped concentration of Yb³⁺ is 20%, the quantum efficiency is as high as 177.9%.Thirdly, we researched the down-conversion process in tellurate glasses co-doped by Er³⁺ and Yb³⁺. When excited by 376 nm, Er³⁺ was excited from the ground state to ⁴G_11/2 excited state. Then cross relaxation energy transfer Er³⁺(²H_11/2) + Yb³⁺(₂F_7/2)?Er³⁺(⁴I_13/2) + Yb³⁺(²F_5/2) was observed. At the same time, through cooperative energy transfer, the photons on ⁴F_7/2 state are transferred to two Yb³⁺ ions, thus near-infrared quantum cutting is realized.