The Preparation Of NaYF₄ Micro/nanocrystals And The Enhancement Of Their Up-conversion Luminescence Properties

Rare earth doped upconversion materials has attracted wide interests due to its potential application in sensor,drug therapy,solar cells and biological imaging etc.Preparation of rare earth ions doped photoluminescence materials with controlled morphology was desired to fulfill the requirement of different applications,which can be used to control its optical properties.Therefore,it is of great research value to control the microscopic morphology.In recent years,the upconversion materials based sensor exhibits the great application value.However,the upconversion efficiency of upconversion materials,especially upconversion nanoparticles,is low,which limits the application of upconversion nanoparticle sensors.Thus,it is crucial to improve the upconversion efficiency.Mthods such as metal nanoparticles,core-shell structures,photonic crystals can be used to enhance upconversion luminescence.In this paper,the effects of rare earth ions doped Na YF4 crystals on the morphology,growth mechanism and optical properties were studied.In addition,the effects of coupling metal nanoparticle plasmon resonance and photonic crystal on the upconversion luminescence properties of Na YF4 nanoparticles were investigated.In the work,rare earth ions doped convex-lens like Na YF4 microcrystals were prepared by adjusting preparation parameters including the reaction time,reaction temperature,Na OH concentration,ratio of oleic acid to 1-octadecene and types of doping ions.A possible growth mechanism is proposed based on reaction time and temperature dependent morphology evolution.With the increasing of reaction time and temperature,the formation processes of transforming from the nanoparticles to convex-lens like Na YF4 microcrystals includes self-assemble,dissolution–nucleation and regrowth.The upconversion luminescence and the corresponding luminescence mechanism were obtained in the various rare earth ions doped convex-lens like Na YF4 microcrystals under the excitation of 808 nm.Compared with microplates and nanoparticles,convex-lens like Na YF4 microcrystals had the highest upconversion luminescence intensity,which can be ascribed to the optical focusing property under the excitation of 808 nm.The Au nanoparticls/photonic crystal hybrids were prepared by sintering method.The hybrids substrate result in the enhancement of excited electric field,which can be served as the template of upconversion emission enhancement of Na YF4: Yb3+,Er3+ nanoparticles excited at the 980 nm.The corresponding maximum upconversion emission enhancement was about 17-fold.What’s more,the detection of Rhodamine B was realized by monitoring the changing of green upconversion intensity of Na YF4: Yb3+,Er3+ nanopartcles.The sensor sensitivity of Na YF4: Yb3+,Er3+ nanoparticles deposited on the Au nanoparticles/photonic crystal hybrid was increased by about the 35-factors,which exhibits a low detection limit of 164 μM and a high sensitivity of 1.15 μM-1.A hybrid substrate with ultra-wideband absorption of Ag structure and photonic crystal was prepared by magnetron method.The coupling of ultra-wideband Ag plasma absorption from UV to NIR and photonic crystal greatly enhances the upconversion luminescence efficiency of Na YF4: Yb3+,Er3+ nanoparticles.The enhancement factor of green emission at 521 nm and red emission at 656 nm was 74-fold and 33-fold,respectively,which is four times than the narrowband absorption of Au/photonic crystal.It can be ascribed to the largely enhancement of excitation field due to the overlapping of excitation wavelength and the ultra-wideband plasma absorption.