Up-conversion Luminescence Properties Of Highly Efficient Ag/ZnO Nanowire Array/rare-earth Doped Oxide Composite Film And Its Application

Up-conversion luminescence（UCL）of rare-earth doped materials has been the subject of much attention due to their wide range of applications in optoelectronics devices,new light source,optical sensing,cellular imaging and disease diagnosis,etc.Oxide materials have wide transparency range and high thermal,mechanical and chemical stability,which can bear extreme conditions of execrable environment.However,most oxide materials have a relatively high optical phonon energy,leading to the low luminescence efficiency for rare-earth doped oxide materials.Therefore,we explored an oxide host material with a relatively low optical phonon energy and high luminescence efficiency.Furthermore,the UCL of rare-earth doped oxide host material was enhanced up to almost two orders of magnitude.Photovoltaic conversion,temperature and rhodamine B sensing properties were also studied.The main achievements are as follows:（1）A facile coprecipitation method was used to prepar Er³⁺ doped YbMoO₄ phosphor.The solution pH value and the sintering temperature have an important effect on the structure of the YbMoO₄.A single tetragonal phase of YbMoO₄ was formed by controlling the solution pH value of about 7 and the sintering temperature of 773 K.The hexavalent molybdenum was reduced to pentavalent molybdenum by thermal-reduction.Both up-conversion（UC）and down-conversion emission properties of Er³⁺:YbMoO₄ phosphors originating from the transitions of ²H_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2→⁴I_15/2 were observed under 980 and 325 nm excitation.The strongest intensity was obtained from the mole ratio of Er:Yb=1:10.The effect of temperature on the up-conversion emissions properties was studied and can be adequately explained by the thermal quenching model.The fluorescence intensity ratio（FIR）of green up-conversion was investigated as a function of temperature.（2）Magnetron sputtering,hydrothermal and spin-coating methods were used to synthesize Ag/nw-ZnO/RE UCL composite film contains of three individual Ag,nw-ZnO layer and rare-earth doped oxide host material.UCL for Ag/nw-ZnO/RE films as a function of the power density was also studied under 980 nm laser excitation.After optimization the lengths of Ag/nw-ZnO/RE composite film,a UCL enhancement of about two orders of magnitude,compared with the individual RE layer,was achieved.Finite Element Method simulations of the electric field distribution inside the realized structures with different geometry were carried out and proved the UCL enhancements attributed to the formation of strong local electric field on the top of nw-ZnO.（3）Photovoltaic conversion,temperature and rhodamine B sensing properties of Ag/nw-ZnO/RE composite film were also studied.The fluorescence intensity ratio of the two green UC emissions was studied as a function of temperature.The maximum sensitivity was approximately 0.01574 K^-1,,which is higher than that of Er³⁺-based sensing materials.The fluorescence intensity ratio of the two green UC emissions exhibits an excellent exponential relationship with the RhB concentration in the range of 0-1000 ppm,which is ascribed to the radiative energy transfer from the composite film to RhB molecules.The photocurrent of the Ag/nw-ZnO/RE composite film is increased by about one order of magnitude as compared to that of Ag/nw-ZnO film under 980 nm excitation,demonstrate the Ag/nw-ZnO/RE composite film has certain application potential in photovoltaic conversion.