The Synthesis Of Several Oxide Up-conversion Materials And The Study Of Their Spectral Properties

Upconversion luminescent materials on oxide system satisfy great application prospects in biomedical imaging,anti-counterfeiting identification,and temperature sensing due to its excellent thermal atability and good luminescence properties.At present,the upconversion luminescent materials are mainly synthesized by solid phase method,high temperature pyrolysis method and solution combustion method.Though these methods are simple to prepare,the morphologies of obtained samples are uncontrollable and the size is large which is not suitable for some special fields.In this paper,several oxide crystals with relatively low phonon energy,such as Gd₂O₃,La₂Te₄O₁₁,Gd₂TeO₆,were selected as host materials and the high-performance upconversion luminescent materials incorporated with rare earth ions of Yb³⁺,Er³⁺,Ho³⁺were synthesized by solution?or liquid phase assisted?conditions The effects of different preparation conditions on structure and morphology of the products were studied,the doping concentration of rare earth ions was optimized and the energy transfer process between rare earth ions was analyzed in detail.The specific research contents are as follows:?1?Material preparation by solution?or liquid phase assisted?conditions.?1?The Gd₂O₃:Yb³⁺/Er³⁺/Ho³⁺cubic structure nanocrystals were prepared by co-precipitation method,and the effects of different calcination temperature and rare earth ion doping concentrations on their phase and morphology were compared;?2?La₂Te₄O₁₁:Yb³⁺/Er³⁺was prepared by hydrothermal method and the hydrothermal reaction parameters were optimized.Meanwhile,the effects of surfactants on final morphologies of samples were studied;?3?Gd₂TeO₆:Yb³⁺/Er³⁺was prepared by hydrothermal method and late calcination.The effects of calcination temperature and rare earth ion doping concentrations on the desired phase were explored.?2?Optimizing upconversion properties by changing doping concentrations.?1?Through the comparison of the upconversion luminescence properties of different rare earth concentrations,it was found that the Gd₂O₃:Yb³⁺/Er³⁺?15/1?obtained a brighter red light under the 980nm near infrared laser.When doped with Yb³⁺/Er³⁺/Ho³⁺?15/1/0.5?concentration,a bright yellow-green light is obtained.?2?Among the La₂Te₄O₁₁1 nanophosphors,the strongest green luminescence and the greatest total luminescence intensity were obtained by doping Yb³⁺/Er³⁺?5/1?,and the green luminescence intensity accounted for 77%of the total luminous intensity.?3?Among the Gd₂TeO₆ nanophosphors,the highest green emission intensity was obtained by doping Yb³⁺/Er³⁺?15/1?,and the green emission intensity accounted for 59%of the total luminous intensity.).?3?Discussing the possible energy transfer mechanisms of different host materials based on the correspondence between the upconversion luminous intensity and the excitation power.?1?For Gd₂O₃ nanophosphor,the red and green emission of Yb³⁺/Er³⁺co-doped system is a two-photon process,while Yb³⁺/Er³⁺/Ho³⁺triple doped system is a three-photon process.Under the excitation of UV characteristic absorption wavelength light of Er³⁺and Ho³⁺respectively,the emission spectra of the Gd₂O₃:Yb³⁺/Er³⁺/Ho³⁺?15/1/0.5?nanocrystals proved that there is an energy transfer process between Er³⁺and Ho³⁺.?2?For the tellurite matrix(La₂Te₄O₁₁/Gd₂TeO₆),the red green emission of Yb³⁺/Er³⁺co-doped nanocrystalline materials is a two-photon process.?4?Studying the temperature sensitive properties of upconversion luminescent based on the dependence of FIR and temperature.?1?For Gd₂O₃ nanocrystals incorporated with rare earth ions,the relationship between the upconversion emissions red green FIR and temperature proved that the max relative sensitivity of Yb³⁺/Er³⁺co-doped was 0.00664K^-1 which obtained at 573K and Yb³⁺/Er³⁺/Ho³⁺co-doped was0.00572K^-1 which obtained at 348K.?2?The upconversion emissions of two thermal coupled levels of ²H_11/2 and ⁴S_3/2 of Er³⁺proved that the maximum sensitivity was0.0089K^-1 obtained at 448k in La₂Te₄O₁₁ and 0.0082K^-1 obtained at T=548k in Gd₂TeO₆.The above upconversion materials have potential application in temperature sensing.The research results also provide a reference for exploring the preparation,performance and application of rare-earth ion-doped oxide luminescent materials.