Fabrication, Luminescent And Energy Transfer Processes Of Rare-earth Doped ?-NaYF₄ Phosphors

In recent years,NaYF₄ especially the hexagonal phase materials have been one of the most effective host materials for performing multicolor down-conversion?DC?and up-conversion?UC?luminescence of rare-earth ions due to its excellent performances,including low phonon energy?< 400 cm-1?,high thermal and optical stability,good transparency,lower non-radiative decay rate and higher radiation emission frequency.However,the optical absorption of rare earth ions(such as: Eu³⁺,Tb³⁺,Dy³⁺ etc.)is low,which leads to low excitation efficiency and luminous intensity,narrow absorption band and small cross section of optical absorption.Therefore,a facile preparation method of rare-earth doped ?-Na YF4,which can enhance the luminous efficiency and absorption rate,has been a significant work.In view of above problems,the following three parts results were obtained in this paper:1.First,the influences of experimental conditions on synthesizing ?-NaYF₄ microcrystals through solvothermal method were systematically studied.Under the optimal process,using EG as solvent,keeping the molar ratio of Y³⁺: F-= 1: 24,carrying out for 6 h under 180 oC,pure ?-NaYF₄: Eu³⁺ microcrystals were synthesized with different Eu³⁺ concentration.Then,the luminescence characteristics of Eu³⁺ doped ?-NaYF₄ microcrystals were studied and the quenching concentration was also identified.2.The optimal process to prepare uniform ?-NaYF₄ crystals using oleic acid?OA?as surfactant by solvothermal method was studied.Hexagonal prism bipyramids ?-NaYF₄ microcrystals with uniform particle size were obtained.Not only the particle size has been decreased,morphology has been regulated,but also the luminescence intensity has been improved about 10 times.At the same time,the quenching concentration of Eu³⁺ has been identified.3.Ce³⁺/Tb³⁺ double-doped and Ce³⁺/Tb³⁺/Eu³⁺ tri-doped ?-NaYF₄ luminescent materials using OA as surfactant were synthesized by solvothermal method.The energy transfer processes between and among Ce³⁺,Tb³⁺ and Eu³⁺ ions were systematically investigated,thus multicolor tunable luminescence ?-NaYF₄ materials co-doped by rare-earths were successfully prepared.It was found that the average particle size decreased with the increasing concentration of rare-earth which had larger ionic radius than Y³⁺.Compared with Eu³⁺ or Tb³⁺ single-doped ?-NaYF₄ materials,the ?-NaYF₄ luminescent materials sensitized by Ce³⁺ could be excited under a broadband range of UV light,but the corresponding optical absorption rate could be enhanced greatly.