Study On The Modulation Of Rare Earth Luminescence By Inorganic Semiconductor Quantum Dots And Its Applications

Rare-earth luminescent materials,due to their rich energy levels and transition characteristics of 4f electrons,display multi-color light emission,narrow emission lines,high color purity,wide emission wavelength distribution area,long lifetime and other characteristics unmatched by other light-emitting materials,which had been widely used in lighting and display areas.Meanwhile,rare earth luminescent materials are also ideal materials for photonic energy conversion in solar cells,which can significantly increase the efficiency of solar cells.However,due to the small absorption cross section and low luminescent efficiency of rare earth materials,applications of rare earth luminescent materials in many fields are seriously restricted.In addition,due to the rapid development of new lighting and display technologies?such as LED lighting,liquid crystal display?,some traditional rare earth lighting and display materials?such as CRT,PDP fluorescent powders?are gradually replaced.At the same time,to enhance the energy conversion efficiency of solar cells by rare earth light conversion materials is still in the laboratory research stage.Therefore,the exploration of highly efficient and stable new rare earth luminescent materials and the application of rare earth luminescent materials in some emerging fields are of great significance for the development and application of rare earth luminescent materials.In this paper,we focus on the problems of upconversion and quantum cutting luminescence in rare earth nano-luminescent materials.The rare earth upconversion luminescence was enhanced by the plasmon resonance and energy transfer effect of Cu_2-xS semiconductor quantum dots,and the maximum enhancement was 1500 times,which was applied to the field of anti-counterfeit displays and perovskite solar cells.The rare earth ions Yb³⁺and Ce³⁺doped in the perovskite quantum dots led the efficiency of the rare earth quantum cutting efficiency reach 146%,and they can be applied to silicon solar cells to increase their energy conversion efficiency from 18.1%to 21.5%.The main results achieved are as follows:[1]Cu_2-xS plasma semiconductor quantum dots were synthesized and their optical,electrical and optoelectronic properties were systematically studied.The surface plasmon resonance in Cu_2-x-x S QDs originated from the collective oscillation of the carriers in the local ligands.It is found that the heat treatment causes the oxidative decomposition of the surface ligands,which causes the plasmon resonance absorption peaks to broaden,weaken and redshift.The localized surface plasmon resonance of Cu_2-xS was used to enhance the upconversion fluorescence intensity of NaYF₄:Yb³⁺,Er³⁺nanoparticles,and an 80-fold optimal enhancement was obtained;the co-enhancement mechanism of two-photon energy transfer process and surface plasmon effect was revealed.[2]A three-dimensional opal photonic crystal and Cu_2-xS plasma quantum dot composite structure were prepared,and their interaction with upconversion nanoparticles NaYF₄:Yb³⁺,Er³⁺@NaYF₄ were systematically studied at various excitation wavelengths?808,980,and 1540 nm?.Combining the photonic crystal effect,surface plasmon resonance effect and two-photon energy transfer process,an up-conversion enhancement of up to 1500 times was achieved,and the fluorescence brightness could reach 1282 cd/m².Finally,a novel angle-dependent infrared anti-counterfeiting was successfully achieved using the composite film.[3]The mCu_2-xS@SiO₂@Er₂O₃ core-shell composite material was synthesized and at an excitation power of 800 mW/mm² 1,100-fold upconversion fluorescence enhancement was achieved,resulting in highly efficient broadband white light emission with internal quantum efficiency as high as 14.3%.Finally,the composite material was applied to enhance the energy conversion efficiency of the perovskite solar cell with efficiency increasing from 16.2%to 17.8%,and the efficiency of the perovskite solar cell was further increased to 18.8%under 15 sunlight.[4]Yb³⁺-doped,(Yb³⁺,Er³⁺)and(Yb³⁺,Ce³⁺)co-doped CsPbCl_x Br_3-x quantum dots were synthesized for the first time.These quantum dots have both perovskite exciton emission and strong infrared emission of Yb³⁺at 988 nm.Due to the efficient quantum cutting luminescence process,the quantum efficiency of CsPbCl_1.5Br_1.5:Yb³⁺and Ce³⁺reached 146%.A simple liquid deposition method was used to successfully self-assemble perovskite quantum dots on the surface of commercial silicon cells,which increased the energy conversion efficiency of silicon cells from 18.1%to 21.5%,a relative increase of 18.8%,far exceeding the previous literature reports.result.[5]Broadband emission derived from defect states was observed in Yb³⁺-doped CsPbCl₃,CsPbCl_1.5Br_1.5,and CsPbBr₃ perovskite quantum dots through temperature-dependent photoluminescence spectra.A microscopic physical model was established to quantitatively simulate temperature-dependent exciton emission,defect luminescence,and Yb³⁺infrared luminescence.The thermal activation process from the valence band to the defect states was the main reason for the variation of the emission intensity of the perovskite exciton emission.The defect state energy level can be used as the intermediate state energy level for the perovskite quantum dot to Yb³⁺ions,leading to a great enhancement of Yb³⁺luminescent efficiency.