Preparation And Luminescent Properties Study Of Quantum Cutting And Quantum Dot Materials

Nowadays,photovoltaic power generation is developing rapidly and gradually replacing traditional energy sources.Solar cells can convert light energy into electricity through the photovoltaic effect.However,because of the band gap of silicon solar cells,the spectral mismatch phenomenon has occurred,resulting in the low conversion efficiency of solar cells.Quantum cutting,as an effective spectral modification method,has became the research focus.The solar spectrum after quantum cutting can improve the conversion efficiency of solar cells.At the same time,quantum dots have also received widespread attention in recent years for their good physical and chemical properties.The carbon quantum dots have low cost,low toxicity,stable chemical properties and good biocompatibility,which makes them widely used in the fields of bioimaging,photocatalysis,display and other fields.The aim of this paper is to improve the conversion efficiency of solar cells through spectral modification method.At the same time,the adjustment of the optical properties of carbon quantum dots by adjusting the solvent was studied.The main research contents and results of this article are as follows:In the first part,the luminescent properties of Pr³⁺ and Yb³⁺ co-doped YPO₄ samples were studied,and the possible energy transfer mechanism between Pr³⁺ and Yb³⁺ was discussed.Experimental results show that ³P0?³HJ?J = 4,5,6?,³FJ?J = 2,3,4?and ¹D₂?³HJ?J = 4,5?and ¹G₄?³H₄ are observed in Pr³⁺ single-doped YPO₄.The filling of intermediate level ¹D₂ is caused by non-radiative transitions and cross-relaxation of ³P0 multiphonons.With the increase of Yb³⁺ concentration,the emission intensity and lifetime of the ¹D₂ and ¹G₄ energy levels decreased,while the emission intensity and lifetime of the ³P0 energy level did not change significantly.This result shows that the ³P0 energy level does not participate in the energy transfer from Pr³⁺ to Yb³⁺,while the ¹D₂ and ¹G₄ energy levels play an important role in the energy transfer process from Pr³⁺ to Yb³⁺ ions.In the second part,the luminescence properties of Pr³⁺ and Yb³⁺ co-doped La BWO₆ samples were studied,and the possible energy transfer mechanism between Pr³⁺ and Yb³⁺ was discussed.We successfully synthesized La BWO₆: 1% Pr³⁺,x% Yb³⁺?x = 0,1,2,3?powder samples which were prepared by high temperature solid method.Under the excitation of 448 nm,Pr³⁺ ions have strong emission in the visible light region,the strongest emission peak is located at 544 nm from ³P0?³H₅ of Pr³⁺ ion,and has emission which cause by ²F_5/2?²F_7/2 of Yb³⁺ in the near infrared region.With the increase of concentration of Yb³⁺,the lifetime of the ³P0 energy level of Pr³⁺ ion decreases,which also proves that there exists energy transfer between Pr³⁺ and Yb³⁺ ions.The third part presents the synthesis and application of carbon quantum dots.We used citric acid as the carbon source,urea as the nitrogen source,and water and N,N-Dimethylformamide as solvents to synthesize blue and green carbon quantum dots at the same temperature.The fluorescence spectrum of carbon quantum dots covers the visible spectrum from 440 nm to 550 nm.By characterizing the structure and optical properties of carbon quantum dots,we found that with the change of the surface state of the carbon quantum dots,the fluorescence emission wavelengths of the carbon quantum dots appear red-shifted.