Synthesis Of Tm³⁺ Doped Fluoride And Oxide By Molten Salt Method And Study On Special Green Emission

There are many methods for synthesis of upconversion?UC?luminescence materials,such as high temperature solid-phase synthesis method,hydrothermal synthesis method and so on.However these methods have their own shortcomings,the temperature is not uniform in the synthesis process of high temperature solid phase synthesis method and samples have different size.Hydrothermal synthesis reaction requires relatively closed space and so on.In order to overcome the above disadvantages,a new synthetic method of the molten salt method?MSS?was used to synthesize the target product.The MSS provides a half of flow reaction environment,the doped ions are uniformly incorporated into the product.The method improves the yield of the sample and saves the reaction time.The target products have uniform size,good crystallinity and high purity.A series of Yb³⁺/Tm³⁺ or Yb³⁺/Tm³⁺/Mn2+ co-doped ?-NaYF4 crystals have been successfully synthesized via the MSS.X ray powder diffraction?XRD?characterization indicates that the ?-NaYF4 is hexagonal phase.The UC emission spectra was measured with an Edinburgh Instruments FLS920 spectrophotometer with a continuous-wave 980 nm laser as the excitation source.A unique strong green emission of Tm³⁺ was observed,which cannot be obtained by any other methods.The red,green and blue?RGB?light emissions have been obtained simultaneously at the presence of a single activator(Tm³⁺).The influencing factors of crystal growth have been studied in detail,in order to understand the change of the transition probabilities of Tm³⁺.Subsequent studies indicate that the RGB light emissions of Tm³⁺ can be effectively tuned by varying the concentration of sensitizers(Yb³⁺ and Mn2+)and the reaction time.Consequently,the effective multicolor UC luminescence was obtained,especially a strong white light,which was not obtained in the ?-NaYF4: Yb,Tm system before.To our knowledge,it is the first time to investigate the UC properties in the ?-NaYF4: Yb,Tm system by altering the transition probabilities at the same energy level of Tm³⁺.As the main material for UC luminescence,the oxides have high chemical stability and low phonon energy?<600 cm-1?,which has good UC luminescence efficiency.In order to further explore the influence of the MSS method on oxide synthesis,a series of Yb³⁺/Tm³⁺ co-doped Y2O3 crystals have been synthesized by utilizing the MSS method.By XRD diffraction and scanning electron microscopy?SEM?image analysis,the sample has good crystallinity and no other impurity phase.The reaction factors have been investigated in detail,in order to understand the impact of these factors on the UC luminescence properties in this system.It was found that using the direct purchase of Y2O3 synthesized Yb³⁺,Tm³⁺ doped oxide can get bright white light.Furthermore,the multicolor UC luminescence was obtained by controlling the reaction time.The study showed that Yb³⁺,Tm³⁺ doped oxide was synthesized by the MSS can also obtain multicolor UC luminescence and bright white light.This study broadens the MSS application of luminescent materials.