Laser Excitation-activated Self-propagating Sintering Of Microcrystal Phosphors

In recent years,up-conversion fluorescent materials have become the focus of research due to their special properties and wide applications.Compared with traditional organic dyes and semiconductor quantum dots,up-conversion fluorescent nanomaterials have many advantages as biomarker nano-probes,such as narrow-band emission,high signal-to-noise ratio,photobleaching resistance and low toxicity.In the past decade,scientists have done a lot of researches on the manipulation of the size,phase,chemical composition and properties of up-conversion fluorescent nanomaterials.At present,water/solvo-thermal method is the main method to prepare up-conversion materials,but the low reaction efficiency and stringent reaction conditions restrict the development of large-scale application of synthetic materials.In this paper,a method of up-conversion fluorescent materials synthesized by laser self-propagating diffusion sintering is proposed.In order to facilitate the analysis and elaboration,we take the synthesis of NaYbF₄:Pr³⁺/Gd³⁺white light phosphor as an example.Using sodium fluoride,ytterbium fluoride,praseodymium fluoride and gadolinium fluoride as raw materials,after ball milling and homogeneous mixing,laser-stimulated sintering reaction took place under 980 nm laser exciting.Finally,the up-conversion white fluorescent materials with strong up-conversion luminescence efficiency?5%?,adjustable phase and practical application scenarios were prepared.XRD,SEM,TEM and spectroscopy were used to test,characterize and analyze the synthesized materials,and the mechanism of the reaction was demonstrated.In this paper,the experimental parameters affecting the chemical reaction and the biological characteristics of the products were explored.By changing the composition and molar content of doped ions in raw materials,the transformation of NaYbF₄ matrix from cubic phase to hexagonal phase can be regulated;by changing the type of doped ions in raw materials,the fluorescence spectrum can be regulated;by changing sintering time and laser power density,the size and fluorescence intensity of the products can be regulated.It is worth mentioning that the anion environment of doped ions has a great influence on the phase transition process.The laser self-propagating diffusion sintering method proposed in this paper is theoretically suitable for the synthesis of any solid-solid reaction products.Therefore,this paper also studied the process of synthesizing calcium copper titanate and thermal barrier coating materials with this method,found the best reaction conditions,and characterized and analyzed the synthesized products.Finally,the dielectric constant of the crystal reaches 10⁴,which can be kept constant in a wide range of low frequencies?¹0⁵ Hz?.