Synthesis And Luminescence Properties Of Halide Perovskite Quantum Dots And Halide Perovskite Derivatives

As a new photoelectric material,halide perovskite has the advantages of flexible and adjustable crystal and electronic structure,high PLQY,adjustable emission wavelength,narrow emission half-peak width,high absorption coefficient and long carrier diffusion length.It has been widely studied in light-emitting diodes,solar cells,photodetectors and other potential applications.Among them,lead halide perovskite quantum dots have high fluorescence efficiency and color purity,and have broad application prospects in the field of backlight display.However,the ionic properties of lead halide perovskite quantum dots make them vulnerable to the effects of light,heat,water and oxygen when exposed to the environment,resulting in the degradation of optical properties.Therefore,to improve its stability is the key to realize its commercial possibility.To this purpose,we successfully synthesized ligand-free Cs Pb Br₃QDs-KIT-6@Pb Br（OH）composite by solvo-free high temperature solid phase method,using KIT-6 molecular sieve as the template of quantum dot growth restriction.Even though the stability of lead halide perovskite materials can be improved,the intrinsic toxicity of lead will eventually make it unable to be used in some subdivisions,such as wearable optoelectronic devices,etc.In view of this,we synthesized several zinc halide perovskites with 0D structure.The three zinc halides in the second part of this paper have emission properties of blue,green and red,respectively.In the third part of this paper,the cyan blue to green adjustable emission and single white emission properties of two doped zinc halides are achieved.The specific content is summarized as follows:1.By solvent-free high temperature solid phase method,Cs Pb Br₃QDS-KIT-6composites were successfully synthesized using KIT-6 molecular siolite as the growth restriction template of quantum dots.It is interesting that Cs Pb Br₃QDs under the semi-protective framework of KIT-6 could spontaneously hydrolyse when encountering water.Furthermore,Cs Pb Br₃QDs-KIT-6@Pb Br（OH）composites with excellent green emission properties were obtained,including～73%photoluminescence quantum yield（PLQY）and 25 nm narrow emission half-peak width.In addition,the composite exhibits significantly enhanced water/heat/light stability due to the dual packaging of Pb Br（OH）and KIT-6.These include water stability with no attenuation of fluorescence intensity after 60 days of immersion in water,thermal stability with heating-cooling cycle at 120℃,and optical stability under continuous ultraviolet irradiation.In addition,the composite can be used as a green phosphor to construct Wleds with wide color gamut and high stability under different operating currents.This study not only provides a reference for the simple solid-state synthesis of highly luminous and stable Cs Pb Br₃quantum dots,but also demonstrates the possibility of mass production of lead halide perovskite quantum dots in commercial lighting and display technologies.2.Three zinc bromide compounds with red,green and blue luminescence were synthesized by simple precipitation method:Cs₂Zn Br₄:Sn²⁺,Cs₂Zn Br₄:Mn²⁺,C₆H₁₆N₂Zn Br₄,with corresponding maximum PLQY of 25%,39%and 21%,respectively.Detailed spectral analysis shows that the 525 nm-centered green light emission in Cs₂Zn Br₄:Mn²⁺is originated from the ⁴T₁（G）-⁶A₁（S）transition of Mn²⁺ions embedded in Cs₂Zn Br₄tetrahedron.Wide-band red light emission centered at635 nm in Cs₂Zn Br₄:Mn²⁺is derived from self-trapping exciton emission generated by[Sn Br₄]^2-structural distortion trapping excitons in Cs₂Zn Br₄:Mn²⁺.Wideband blue emission at 454 nm in the hybrid structure C₆H₁₆N₂Zn Br₄is from high structural deformation and STEs radiation recombination caused by strong electron phonon coupling.Our work on blue,green and red luminescent materials based on lead-zinc halide free has not only provided new feasible solutions for the application of white leds,but also promoted the discovery of alternative materials for lead halides.3.Pb²⁺doped Cs₂Zn Br₄microcrystals powder was synthesized by precipitation method.By adjusting the feed ratio of Pb²⁺,the adjustable emissions from blue（495nm）to green（518 nm）from Cs₂Zn Br₄:Pb²⁺are achieved.We believe that the blue-cyan to green tunable emission is due to the rapid capture of photoexcitons in the[Pb Br4]^2-tetrahedron and localized exciton emission in the[Zn Br₄]^2-tetrahedron.Further,Mn²⁺is introduced into the Cs₂Zn Br₄:Pb²⁺lattice by precipitation method.Surprisingly,Mn²⁺&Pb²⁺co-doped Cs₂Zn Br₄microcrystals achieve cyan（500 nm emission center）and orange-red（625 nm emission center）dual-mode emission.It is confirmed by spectral analysis that the orange-red emission is from the d-d orbital transition caused by the energy transfer from exciton to Mn²⁺ions in Cs₂Zn Br₄:Pb²⁺.Finally,by regulating the doping ratio of Pb²⁺and Mn²⁺,Cs₂Zn Br₄:Pb²⁺&Mn²⁺microcrystals with single white light emission are obtained.The white light emission of Cs₂Zn Br₄:Pb²⁺&Mn²⁺microcrystals can be tuned from cold white light to warm white light.Due to the zero-dimensional structure and tetrahedral framework of Cs₂Zn Br₄,the codoped Cs₂Zn Br₄:Pb²⁺&Mn²⁺microcrystals not only possess significant white light emission properties,but also have good stability.Therefore,our work is not only expected to be used as a white light source in solid state lighting.It can provide reference for the discovery of lead-free/less lead halide luminescent materials.