Preparation Of Sub Au Nanoparticles Coated On Upconversion Nanoparticales And Its Application In High Efficiency Photothermal Conversion

Gold(Au)nanoparticles can efficiently convert light into heat through surface plasma effect,thus significantly improving the ambient temperature.This photothermal effect has been applied to solar energy,cancer,gene release,drug delivery and other fields,and has shown excellent performance.Photothermal conversion is one of the important properties of gold nanoparticles.However,up to now,the mechanism of photothermal conversion of gold nanoparticles has not been fully revealed,and the key factors affecting the efficiency of photothermal conversion have yet to be determined.In this paper,we use upconversion nanoparticles(UCNPs)with high sensitivity and selectivity as nano light source,whose emission wavelength is 540nm(green light),which can be effectively absorbed by sub nano gold particles with an average diameter of 4nm coated on the surface.In this paper,the UCNPs@Au composite nano system can be controlled by solvothermal method.The absorption characteristics,fluorescence characteristics,energy exchange,photothermal conversion mechanism and efficiency of UCNPs@Au system are analyzed.It is proved that the fluorescence resonance energy transfer(FRET)mechanism is the main way to realize this efficient nano photothermal conversion system(UCNPs@Au),rather than the direct photon absorption.The main contents are as follows:1.Using solvothermal method and the catalysis of short wave ultraviolet to synthesize the UCNPs@Au nano system with stable structure and good shape consistency.2.In UCNPs@Au system,ucnps play the role of energy donor,while gold nanocrystals play the role of energy acceptor.Gold nanocrystals can effectively absorb the green emission of ucnps,resulting in a 76.01%reduction in upconversion emission,which can be directly measured or observed by upconversion fluorescence.At the same time,it is also verified that fret mechanism is the main way of this efficient nano photothermal conversion(UCNPs@Au)system,rather than direct photon absorption.3.Using up conversion fluorescence and infrared imaging technology,we can directly observe the same real-time high-efficiency photothermal conversion.The physical significance of the power-law function I-P^*nrelated to upconversion luminescence is also verified.