Synthesis And Luminescence Properties Of Rare-earth Doped Gd₂O₃/Gd₂O₂S Micro/Nano-materials

Rare earth doped oxide and oxysulfide luminescent materials are widely used in lighting,imaging display,temperature sensing,glass,ceramics,biomedicine and other fields because of their advantages of high chemical stability,thermal stability,luminescent efficiency,low phonon energy and simple preparation process.Therefore,many researchers have carried out research work on rare earth doped oxide and oxysulfide luminescent materials.However,the following problems still exist in the synthesis and research of these materials:The Gd₂O₃/Gd₂O₂S luminescent materials with cylindrical morphology have not been reported,morphology growth mechanism is insufficient,multi-color tunable luminescence needs to be further enriched,and the influence of matrix cations on morphology and luminescence properties of Eu³⁺doped oxysulfide is not clear.In this paper,the morphology regulation and luminescence regulation of luminescent materials as well as the relationship between the structure,morphology and luminescence properties of Eu³⁺doped oxysulfide are mainly studied.In terms of morphology regulation,a new cylindrical or short rod-shaped rare earth doped Gd₂O₃or Gd₂O₂S phosphors were prepared by solvothermal method,and the growth mechanism of cylindrical morphology and luminescence properties of phosphors were studied in detail.In terms of luminescence regulation,Dy³⁺,Tb³⁺,Eu³⁺,Sm³⁺and other rare earth ions were doped and co-doped in the matrix to achieve polychromatic luminescence and photocolor regulation,and the luminescence mechanism was studied.Finally,in the aspect of structural-activity relationship,the structure,morphology and luminescence properties of Eu³⁺doped Lu₂O₂S,Gd₂O₂S and Y₂O₂S phosphors were studied in order to investigate the influence of matrix cations on morphology and luminescence properties of Eu³⁺doped oxysulfide.The details are as follows:1.Gd₂O₃:Eu³⁺/Tb³⁺phosphors with a new cylindrical morphology were synthesized by solvothermal reaction and subsequent calcination.According to the formation process of the precursor,the growth mechanism of the cylindrical morphology was deduced,which can be divided into three stages:dissolution-recrystallization,self-assembly and growth.The weight loss of precursor was measured and the formation process of Gd₂O₃phase was analyzed.In addition,the luminescent properties of Gd₂O₃:Eu³⁺/Tb³⁺phosphors were analyzed in detail.Under ultraviolet(UV)light excitation,Gd₂O₃:Eu³⁺phosphor exhibits red emission,while Gd₂O₃:Tb³⁺phosphor exhibits green emission.2.Gd₂O₂S:Eu³⁺phosphors with cylindrical morphology were synthesized by solvothermal reaction and subsequent sulfidation calcination.The effect of calcination temperature on sample morphology was discussed,and the optimum calcination temperature is 600°C.The structure,morphology and thermal properties of the sample were analyzed,as well as the spectral characteristics of Gd₂O₂S:Eu³⁺phosphors with different Eu³⁺doping concentrations,which showed red emission.The band-gap,luminescence intensity,luminescence color and fluorescence lifetime of cylindrical Gd₂O₂S:Eu³⁺phosphor were compared with those of cylindrical Gd₂O₃:Eu³⁺phosphor by calculating and discussing the Judd-Ofelt theory.3.Polychromatic luminescence Gd₂O₃:Dy³⁺,Tb³⁺,Eu³⁺phosphors with cylindrical morphology were synthesized by solvothermal reaction and subsequent calcination.The multi-color luminescence properties were achieved by changing the types and doping ratios of rare earth ions in Gd₂O₃.The light color range included green light,red light and blue light,including cold white light and warm white light.It is proved that there is an energy transfer from Dy³⁺to Tb³⁺in Gd₂O₃:Dy³⁺,Tb³⁺systems and from Tb³⁺to Eu³⁺in Gd₂O₃:Tb³⁺,Eu³⁺systems.The mechanism of energy transfer is calculated and analyzed by Blasse formula,Dexter multipole energy transfer theory and Reisfeld approximation theory.4.By increasing the temperature during the calcination process,the modified Gd₂O₂S:Tb³⁺,Sm³⁺phosphors with short rod-like morphology were synthesized.The influence of calcination temperature on morphology was discussed.The energy transfer from Tb³⁺to Sm³⁺in Gd₂O₂S:Tb³⁺,Sm³⁺systems is proved,and the mechanism of energy transfer is analyzed.By changing the doping amount,proportion of the two rare earth ions and changing the excitation wavelength of the phosphor,the adjustable luminescence from green light to orange-red light can be realized.5.RE₂O₂S:Eu³⁺phosphors with various morphologies were synthesized by solvothermal synthesis and subsequent sulfidation calcination,where RE is Lu,Gd and Y,respectively.Under the same preparation conditions,RE₂O₂S:Eu³⁺phosphors with different morphologies were obtained by changing only the matrix cations.The morphologies of Lu₂O₂S:Eu³⁺,Gd₂O₂S:Eu³⁺and Y₂O₂S:Eu³⁺phosphors were rod-shaped,cylindrical and long sheet-shaped,respectively.The causes of morphology differences were discussed and the growth mechanism of samples was proposed.The sample structure,morphology,luminescence intensity,Eu³⁺doping position symmetry,band-gap energy and fluorescence lifetime were analyzed in detail.In addition,the thermostability of three phosphors was analyzed.