| At present,white LED devices are generally prepared by exciting blue phosphors with blue GaN chips,and the color rendering index of the devices is not high.In order to improve the color rendering index,white LEDs can be prepared by mixing phosphors of various colors,but such phosphor mixtures generally have disadvantages such as phase separation and chromaticity shift.The use of ultraviolet LEDs to excite single-component white phosphors is one of the effective methods to solve the above problems,and the preparation of high fluorescent quantum efficiency white phosphors has become the key to this method.Lead-based halide perovskite materials have unique defect tolerance,tunable fluorescence wavelength,high fluorescence quantum efficiency and other advantages,and are expected to be used in the preparation of white fluorescent powder with high fluorescence quantum efficiency.This paper focuses on the preparation of white fluorescent halide perovskite nanocrystals.By using the CAS halide perovskite nanocrystals with quantum confinement effect as the host for doping,it overcomes the disadvantage of insufficient energy transfer efficiency in the three-dimensional halide perovskite host material with weak confinement effect,which achieves a higher host-impurity energy transfer efficiency at low doping levels,thus providing new ideas for controlling the nanocrystalline chromaticity.The main contents are as follows:First,the zero-dimensional Mn:CsPb(Cl/Br)3@CsPb(Cl/Br)x core-amorphous shell(CAS)quantum dots were synthesized by hot injection method.The morphology,structure and optical properties of quantum dots were characterized,and the effects of experimental conditions such as Mn/Pb feed ratio,reaction temperature and ice-water bath time on the fluorescence properties of quantum dots were analyzed.Secondly,the PL dynamics of quantum dots were studied.The results reveal that the prepared quantum dots can achieve higher host-impurity energy transfer efficiency at a lower Mn doping amount(6.4%).The energy transfer rate constant from halide perovskite conduction band to Mn dopant is 19.3 times higher than that of the traditional three-dimensional Mn:CsPb(Cl/Br)3 nanocubes.This high energy transfer efficiency at a low doping amount can not only avoid the reduction in fluorescence quantum efficiency caused by the Mn-Mn interaction at a high Mn doping amount,but also enable the energy transfer between the host and impurities to meet the requirements of white light nanocrystals,thereby obtained quantum dots with Commission Internationale de l’Eclairage(CIE)color coordinates of(0.37,0.33),which are close to the standard white light.In addition,the composites prepared by mixing polystyrene and Mn:CsPb(Cl/Br)3@CsPb(Cl/Br)x CAS quantum dot solution to improve stability and color stability.After being irradiated with ultraviolet light at room temperature,the fluorescence intensity of the composites and the fluorescence intensity ratio of the perovskite band edge emission peak to the Mn emission peak remained basically unchanged after the initial stage of fluorescence decreased to 70%of the original intensity.Besides,the CAS quantum dots-polystyrene composites have excellent solution processability,and can be used as both color conversion materials and coating materials.Coating the composites on the hemispherical surface of the ultraviolet LED lamp beads can convert the ultraviolet light of the chip into white light. |
