Research On Preparation And Upconversion Luminescence Propertiesof Er/Yb Co-doped VO₂

Vanadium dioxide（VO₂） can be applied to smart material fie ld because of its character of phase transition. When doped with rare-earth ions, it would be a new promising material that combine the properties of smart materials with upconversion luminescent materials, broadening the range of its applications. In this paper, VO₂ doped with Er3+/Yb3+ powders were synthesized by hydrothermal method and then annealed. The synthesis technology was studied combined with XRD, SEM and Raman, in addition, the property of upconversion was discussed. First of all, the effects of Er3+/Yb3+ concentration and the temperature were studied to analyze the property of upconversion emission. Meanwhile, the UC mechanism for Er3+/Yb3+/ VO₂（M） was discussed as well. Moreover, the electron and band structure of the VO₂（M）, VO₂（R） and Er3+/Yb3+/VO₂（M） were calculated by MS.The best hydrothermal reaction conditions, the reducer ratio, temperature and reaction time was 1:2, 180°C and 24 h respectively, for synthesizing Er3+/Yb3+/VO₂（B） samples can be obtained via orthogonal test. Then those samples were put into tube furnace for 4 h at 600°C. The X-Ray powder diffraction illustrated that VO₂ can maintain its crystal structure as rare-earth ions co-doped and the Raman spectrum indicated a low phonon energy which has the possibility of efficient upconversion emission.The green emissions of Er3+/Yb3+ co-doped VO₂ had been measured with two peaks at 525 nm and 555 nm, due to 2H11/2/4S3/2â†'4I15/2 transition of Er3+ ions under 980 nm emission, respective ly in addition with the red emission peek of 660 nm due to 4F9/2â†'4I15/2 transit ion of Er3+. We can get a pure green emission under 980 nm excitation, because the intensity of red emission is so low that can be ignored.The phase transition temperature（Tc） of Er3+/Yb3+ co-doped VO₂（M） was characterized via DTA. It was previously reported that the pure VO 2（M） exhibited a Tc value at about 68°C while the Tc of Er3+/Yb3+ co-doped VO₂（M） value decreased to 41.4°C. When the temperature was higher than Tc, the Er3+/Yb3+ co-doped VO₂（M） occured phase transition, causing the the result that the emission upconversion increased dramatically and abruptly into the most strongest intensity of emission.