Preparation And Application Of Rare Earth Doped Inorganic Nanoparticles Based On Near-infrared Second Region Fluorescence Emission

Rare earth doped inorganic nanoparticles（LDNPs）are considered as a promising second near-infrared region（NIR-II）fluorescent material.Compared with other NIR-II fluorescent materials,it has characteristics of excellent thermal/chemical stability,anti-photobleaching,hypotoxicity,large Stokes shift,adjustable fluorescence emission wavelength,and fluorescence lifetime.At present,the synthesis of LDNPs has many problems,such as large particle size,low quantum yields（QYs）,complicated synthesis methods,and so on.To meet its industrial application in the fields of portable near-infrared spectrometers,medical devices,biological imaging,etc.,these problems need to be solved.In this paper,we developed novel LDNPs based on two different materials to solve the above problems.The structure and fluorescence properties of Sr₂Ga₂Ge O₇:1.5%Nd³⁺(SGGO:1.5%Nd³⁺)and its application in light-emitting diodes（LEDs）have been studied.Meanwhile,the morphology,size,and fluorescence properties of Na Yb F₄:Tm³⁺,Gd³⁺@Ca F₂ fluorescent nanoprobes have been optimized.The specific research contents are as follows:1.A series of novel M₂Ga₂Ge O₇:N³⁺（M=Ca,Ba,Sr;N=Cr,Nd,Er）samples were prepared by microwave-assisted sol-gel method.Then we focused on the study of Nd³⁺doped SGGO sub-micron phosphors,and systematically studied their structure information and luminescent properties.The tetragonal phase of SGGO belongs to the space group of P4^-21m（113）.The Nd³⁺ions occupy eight-coordinated Sr²⁺sites in the crystal lattice.The gelation time and heat treatment temperature of samples were greatly reduced by microwave treatment and cation substitution,and sub-micron crystals with a particle size of about 220 nm were obtained.It has rich excitation spectra ranging from 350 nm to 850 nm and can produce multiband NIR fluorescence emissions of1331,1056,and 905 nm when excited by blue or NIR light.The internal QYs is 13.3%.The maximum emission intensity was obtained by optimizing the doping ratio of Nd³⁺ions.Then,a commercial chip was utilized to fabricate light-emitting diodes（LEDs）to verify its application potential in NIR mini-LEDs.Compared with commercial blue light LEDs,the as-prepared LEDs had good imaging penetration depth.Because of the simple synthesis process,it has the potential for industrialization.2.A novel Na Yb F₄:Tm³⁺,Gd³⁺@Ca F₂ fluorescent nanoprobe was synthesized by an improved thermal decomposition method.Yb³⁺matrix was selected to increase the absorption cross-section at 980 nm,and the crystal size can be reduced to about 25 nm by doping Gd³⁺.Under the excitation of a 980 nm laser,it can produce 1470 nm fluorescence.The down-conversion luminescence intensity of Na Yb F₄:2%Tm³⁺can be enhanced by 5.5 times by doping 2%Ce³⁺.Finally,the Ca F₂ layer was coated to suppress the concentration quenching and water quenching effects caused by surface defects.Na Yb F₄:Tm³⁺,Gd³⁺,Ce³⁺@Ca F₂ nanocrystals are potential carriers to build multifunctional nano-platforms.