Experimental Study On Improving The Fluorescence Efficiency Of Rare Earth Doped Upconversion Nanomaterials

Rare earth ions doped compounds can be used in three-dimensional display,fluorescence imaging,DNA detection and disease diagnosis with their unique optical,electrical and magnetic properties.Higher luminescence efficiency is the precondition for their applications.Therefore,one main research field of upconversion materials is to improve the efficiency.One of the most important points which can affect the efficiency is the nonradiative decay process.Herein,on the basis of the commonly used rare earth doped oxides and fluorides,two methods to improve the efficiency,including improving the calcination temperature and surface modification were investigated,respectively.In addition,the mechanisms were studied.On one hand,we increased the fluorescence intensity by re-calcination procedure under higher temperature to reduce the crystal defects of the oxide matrix and improve the crystallinity of the samples and thus reduced the energy consumption through nonradiative relaxation processes.By comparing the upconversion characteristics between the precusors and their re-sintering counterparts,it was found that the intensity of the red emission increases significantly compared to that of the green emission.The nanocrystals possessing high color purity under different conditions,even undergoing light saturation,could meet the needs of various potential applications.On the other,we used the core-shell structure to increase the distance between the luminescent centers and surface defects in fluoride matrix,which could restrain the fluorescence quenching and thus increase the fluorescence intensity.Based on the study of the upconversion properties of samples with different shell thickness,the route with appropriate thickness in core-shell structure could be applied in practice.