| New photofunctional materials doped with rare earth(RE3+)ions have advantages such as rich energy level structure,long lifetime,high stability of host materials and flexibility in selecting dopants and host materials.They have extensive applications in laser materials,solar cells,three-dimensional display technology and electroluminescent devices,and has become a hot trend in today's research.In this paper,Tm3+/Yb3+,Er3+/Yb3+and Tm3+/Nd3+/Yb3+pairs were doped with Na5Lu9F32 single crystal by an improved Bridgman method to obtain high-efficiency and stable materials.The optical properties of crystal were verified from XRD diffraction pattern,absorption spectrum,transmission spectrum,emission spectrum,fluorescence decay curve and pump power.Moreover,and the external quantum efficiency of the sample was obtained by the integrating sphere.The introduction part of this paper introduces the background of the topic,the luminescence mechanism and research status of the up-conversion and down-conversion of rare earth doped materials.The crystal structure and excellent properties of Na5Lu9F32 single crystal are introduced,and growth method of the crystal is described in detail.In the second chapter,we studied the growth of Er3+/Yb3+ co-doped Na5Lu9F32 single crystal by the modified Bridgman method as an up-conversion layer incorporated into solar cells to expand the absorption range.The crystal structure and luminescence mechanism of Er3+/Yb3+ co-doped Na5Lu9F32 single crystal were analyzed by XRD diffraction,absorption,transmission and emission spectroscopy.The effectiveness of the prepared materials as spectral converter is verified by the enhancement of power conversion efficiency of perovskite solar cells.Sample with UC layer is 15.5%more efficient to convert sunlight to electricity comparing to the UC layer-free sample due to the absorption of sunlight in the NIR range.The third chapter mainly introduces Tm3+/Yb3+co-doped Na5Lu9F32 single crystal.The upconversion luminescence mechanism and energy transfer process were analyzed by XRD diffraction pattern,absorption spectrum,upconversion emission spectrum,temperature variability spectrum and lifetime decay curve.The cubic dependence of pump power on UC emission reveals that three-photon UC processes are mainly responsible for the 488 nm,704 nm emissions and the quadratic dependence indicates two-photon process for the 805 nm emission in Tm3+/Yb3+co-doped Na5Lu9F32 single crystals,respectively.And the Tm3+/Yb3+ co-doped Na5Lu9F32 has a higher up-conversion quantum efficiency as measured by the integrating sphere.The fourth chapter mainly introduces the improved Bridgman method to grow Tm3+/Yb3+/Nd3+three-doped Na5Lu9F32 single crystal.The optical properties of upconversion and downconversion were analyzed by XRD diffraction pattern,absorption,transmission emission spectrum and fluorescence lifetime curve.The conversion luminescence properties were studied.The effect of the concentration of Yb3+and Nd3+ions on the integrated intensity of DC and UC emission was investigated.Therefore,the optical properties of the prepared material may can be used for a broad range of applications,including solid-state lasers,display,and illuminating technology and solar energy conversion.The last chapter summarizes the content and key results of the experiments,and proposes some plans and suggestions for future researches. |
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