Study On Luminescent Properties Of Mixed Phases Of Inorganic Perovskite Quantum Dots And Rare Earth Upconversion Nanocrystals

In recent years,inorganic perovskite quantum dots CsPbX3(X=Cl,Br,I)have attracted wide attentions of materials scientists because of their excellent luminescent properties,such as easy adjustment of luminescent color,narrow width at half peak and high fluorescence quantum yield,thus can be applied to a variety of optoelectronic fields including light-emitting diodes,single-photon lasers,solar cells and photodetectors.However,the above properties and applications are based on short-wavelength excitation with wavelengths less than 600 nm whose photon energy and power are high.Therefore,the damage to the crystal structure of CsPbX3 is large,and using the near infrared light with low photon energy and large transmission depth to excite CsPbX3 requires a picosecond laser which is expensive and has a high power.Accordingly,how to realize CsPbX3 luminescence under low power near infrared light excitation has high value for its theory and application.In this paper,the mixed phase method will be used to realize the large-scale modulation of excitation and emission wavelength,fluorescence lifetime and color of CsPbX3 quantum dot.The specific research contents are as follows:CsPbX3(X=Br,I)quantum dots were prepared by hot-injection method.The phase and morphology were characterized by X-ray diffraction(XRD)and transmission electron microscopy(TEM),and the luminescence properties of CsPbBr3,CsPbBr1.5I1.5 and CsPbI3 under the excitation of 365 nm ultraviolet light were studied by fluorescence spectrometer.And the influence and mechanism of X species on the wavelength of emission peak were revealed.The rare earth upconverting nanocrystal of NaGdF4:Yb,Tm was prepared by high temperature pyrolysis method,and its luminescent properties were characterized by fluorescence spectrometer.CsPbX3 was ultrasonically mixed with NaGdF4:Yb,Tm,and the mixed phase was excited by 980 nm near infrared light.Under these conditions,NaGdF4:Yb,Tm emits ultraviolet light and blue light which can be absorbed by CsPbX3,and the excitation of CsPbX3 under 980 nm near infrared light was realized through energy transfer between the two materials.Besides,the fluorescence lifetime of quantum dots was prolonged greatly.In addition,the studies were made to change the concentration of Tm3+in NaGdF4:Yb,Tm,the concentration of CsPbX3 in the mixed phase,and the ratio of Br and I in CsPbX3 to control the luminescence intensity,luminescence color and fluorescence lifetime of the mixed phase.NaGdF4:Yb,Tm active nucleus with Tm3+concentration of 1.0%were prepared by high temperature pyrolysis,then NaYF4:Nd,Yb sensitized shell was coated on the surface of NaGdF4:Yb,Tm by epitaxial growth method to obtain NaGdF4:Yb,Tm@NaYF4:Nd,Yb core-shell structure nanocrystal which can be excited by 808 nm near infrared light.CsPbX3 was mixed with NaGdF4:Yb,Tm@NaYF4:Nd,Yb ultrasonically,and the energy transfer between them could realize the luminescence of CsPbX3 under the excitation of 808 nm near infrared light,and the fluorescence lifetime was greatly prolonged.The regulation process and mechanism of the luminescence intensity,luminescence color and fluorescence lifetime of the mixed phase were revealed by changing the concentration of Nd3+ in the sensitized shell and the ratio of Br and I in CsPbX3.