Electrodeposition Of β-NaYF₄:Yb³⁺/Er³⁺ Film And The Study Of Their Un-conversion Luminescence Properties

The upconverting luminescent materials convert low energy near-infrared light into high-energy ultraviolet/visible light by absorbing multiple photons or energy transfer.Among various types of phosphors,rare earth(RE)materials are important and promising materials.NaYF4 is one of the most effective host materials,and the hexagonal phase of β-NaYF4:Yb3+/Er3+ exhibits an up-conversion efficiency that is orders of magnitude higher than that of its cubic counterpart.The mechanism of preparation of NaYF4 thin film by anodic electrodeposition was studied.A method for preparing hexagonal phase NaYF4 thin film at low temperature was developed,which was made through epitaxially electrodepositing onto P-NaGdF4 underlayer at near room temperature(30℃).The formation mechanism,structure,morphology and up-conversion emmision properties of NaYF4 thin films were characterized and studied.The research of this thesis is divided into two parts:(1)Using complex stability constants(RE3+ and EDTA)and pH effect coefficient αY(H)of EDTA,theoretical calculation of free RE3+ ion concentration in solution at different pH values.The electrochemical quartz crystal microbalance(EQCM)technology and cycling voltammetry methods have been used to study the mechanism of electrodeposition of NaYF4 film.Electrodeposition of NaYF4:Yb3+/Er3+ thin film was carried out at 30℃ and the crystal phase of NaYF4:Yb3+/Er3+ was transformed into hexagonal phase from cube phase after annealing at 300 ℃ for 6h.For NaYF4:Yb3+/Er3+ films,with the increase of hexagonal phase content,the upconversion luminescence intensity increases significantly.The up-conversion emission involves a two-photon process.(2)Since the β-NaGdF4 and β-NaYF4 have same hexagonal crystal structures and their lattice parameter difference is less than 1%,the hexagonal phase NaYF4:Yb3+/Er3+ thin film was prepared by epitaxially electrodeposited at near room temperature(30℃)with hexagonal phase NaGdF4 electrodeposited at 50℃ as substrate.The morphology of the film appears fusiform cylinders.After dehydration annealing at 150℃,the intensity of the up-converted luminescence of the hexagonal phase NaYF4:Yb3+/Er3+ film excited by the 980 nm were significantly higher than that of the cubic counterpart.The new method developed in this work should be applied to other systems to obtain a crystal phase that cannot be obtained at low temperatures.