Research On Preparation,Performance And Application Of Rare Earth Doped Fluoride Luminescent System

The research on the preparation and application of up-conversion luminescent materials has seen explosive growth in recent decades,especially in important application areas such as biological imaging,biological probes,photodynamic therapy,temperature sensing,and information security.Because of its attractive chemical and optical properties,including low autofluorescence,strong penetrating ability under near infrared(NIR)radiation,sharp excitation and emission bands and low toxicity.However,the efficiency of up-conversion luminescent is still very low,which greatly hinders their applicability in various fields such as display and lighting.This article summarizes the typical up-conversion luminescence applications in recent years,and also states the three components of up-conversion luminescence materials:matrix material,sensitizer and activator.A host material with low phonon energy and high stability is the goal pursued by researchers,but the importance of size,morphology and structure of upconversion luminescent materials is often ignored.In this paper,?-Na YF₄ mesocrystals with controllable shape,adjustable size,variable structure and cantaloupe-like shape were synthesized by hydrothermal method.The crystal structure and morphology evolution process of?-Na YF₄ mesocrystals were systematically studied under different experimental conditions.The results show that the inherent crystal structure and external factors control the growth process of?-Na YF₄ mesocrystals.The growth process mainly includes dissolution-renucleation,anisotropic growth,subsequent oriented attachment and self-assembly.In addition,the luminescence characteristics of?-Na YF₄:RE³⁺(RE=Ce,Tb,Eu,Yb,Tm and Ho)mesocrystals are studied on the basis of the foregoing,and efficient multi-color up-conversion and down-conversion emission can be easily realized.Moreover,?-Na YF₄:RE³⁺mesocrystals has been successfully applied to fingerprint detection.Subsequently,this paper designs and manufactures a core-shell structure to increase the efficiency of up-conversion.A new type of up-conversion luminescent nanoparticle with a core-shell structure of Na Gd F₄:Yb/Ho/Ce@Na YF₄:X(X=Eu,Tb,Sm,Dy,Eu/Tb)was synthesized by co-precipitation method.In our design,Gd³⁺-mediated interface energy transfer,Ce³⁺-assisted cross relaxation and core-shell structure design are used to achieve efficient dual-mode luminescence with adjustable color output.The experimental results show that under the excitation of 254 nm ultraviolet and 980 nm laser,high-efficiency and multi-color tunable dual-mode emission can be simultaneously observed in the pre-designed core-shell nanostructure.Through the cross-relaxation process between Ce³⁺and Ho³⁺ions in the inner core region,the up-conversion luminescence colors of the as-synthesized samples can be turned from green to yellow and finally to red when adjusting the dopant concentration of Ce³⁺in the core.By selecting Ce³⁺as the sensitizer for harvesting the energy of incident ultraviolet(UV)light and introducing Gd³⁺as the ideal intermediate for subsequent energy migration,the multi-color down-conversion emission of the obtained sample will also be obtained via a Gd³⁺-assisted interface energy transfer processes.The design of the new core-shell structure can not only reduce the surface quenching of the crystal,but also enables the spatial separation of upconverting activators and downshifting centers in order to greatly suppress their adverse cross-relaxation processes.Finally,high-efficiency dual-mode luminescent nanoparticles based on adjustable color output have strong practicability in anti-counterfeiting applications.