The Preparation And Optical Properties Of CsPbX₃ Quantum Dots Composites And Their Application In White LED

All-inorganic CsPbX₃（X=Cl,Br,I）perovskite quantum dots（QDs）have become the current rookie of QDs luminescent materials due to their excellent optical properties such as full spectrum,narrow emission band,high quantum yield.Therefore,they are expected to be promising materials for next generation lighting and display,and many other applications.However,due to the poor stability of CsPbX₃ QDs in air environment and the anion exchange reaction between different halogens,it is a hot research topic to improve the stability of QDs and prevent the occurrence of ion exchange reaction.In this paper,CsPbX₃ QDs solid composites were prepared by the hot injection and heat-treatment approach.Then a series of characterization methods were used to investigate the microstructure and luminescence properties of these solid composites.And finally,white LED devices were fabricated by matching with commercial InGaN blue chips to discuss the application value of QDs solid composites.According to the above research points,the research content of this paper is divided into the following sections:1.CsPbBr₃ QDs solution was synthesized by hot injection method,then QDs was coated by mesoporous silica to obtain QDs nanocomposite.The morphology of the nanocomposite was characterized by X-ray powder diffraction（XRD）and transmission electron microscopy（TEM）.The results show that the nanocomposite shows good crystallinity.Fluorescence spectroscopy（PL）results show that nanocomposites exhibit excellent luminescence properties.compared with QDs solution,the nanocomposite show more excellent chemical and thermal stability,and still emit intense green light in aqueous solution.Those results further illustrated that the introduction of mesoporous silica helps to improve the stability of QDs.Subsequently,white LED devices were fabricated by compounding the prepared CsPbBr₃ QDs nanocomposites with the commercially red phosphor Sr₂Si₅N₈:Eu²⁺and matching with commercial InGaN blue chips.The CIE color coordinates were（0.3365,0.3390）and luminous efficiency reached 47.6 lm/W at a current of 20 mA.Additionally,the white LED device showed excellent color stability when the current was increased to 120 mA.The results indicate that QDs nanocomposite has potential applications in the field of lighting.2.According to the experimental method for preparing CsPbBr₃QDs nanocomposites,we further prepared CsPb(Br_0.4I_0.6)₃ QDs nanocomposites.The results show that CsPb(Br_0.4I_0.6)₃ QDs nanocomposites not only maintain the excellent luminescent properties of QDs solution but also improve the stability of QDs.In addition,mixing of CsPbBr₃ and CsPb(Br_0.4I_0.6)₃ QDs nanocomposites also prevented the occurrence of anion exchange reactions.Therefore,these excellent properties can improve the existing problems of the white LED（low color rendering index and high color temperature）.Subsequently,for the first time,the red CsPb(Br_0.4I_0.6)₃ QDs nanocomposites were used as red phosphor and stacked on the Ce³⁺:Y₃Al₅O₁₂ phosphor-in-glass（Ce-PiG）via screen-printing technology.Then white LED was constructed by combing the nanocomposites with InGaN blue chip,which present outstanding optical performance with a luminous efficiency of 56 l m/W,a high color rendering index of 92 and R9 value up to 90 under 20 mA operational current.In addition,the corrected color temperature and color rendering index of prepared white LED devices did not change significantly after 24 hours continuous operation.These results indicate that red perovskite nanocomposites have potential applications in warm white LEDs.3.The CsPbBr₃ QD glass was prepared by heat treatment approach and the luminescent properties of QD glasses were systematically investigated by changing the heat treatment temperature.The experimental results show that the as-prepared QD glass has excellent luminescent properties and narrow band emission.The chemical and thermal stability of QD glass has been greatly improved,and the QD glass has excellent water resistant properties,which emitted strong green light in aqueous solution even after 24 h.Therefore,benefiting from the excellent performance,QD glass can be used in white LEDs.Then the as-prepared green CsPbBr₃ QD glass was employed to fabricate white LEDs combined with a commercial CaAlSiN₃:Eu²⁺red phosphor on top of a GaN blue chip.The prepared white LED has excellent optical properties,such as the corrected color temperature of 3674 K and color rendering index of 83.4.Therefore,all-inorganic CsPbBr₃ QDs glass offers the possibility to realize the application of white LED with high performance and low energy consumption.