Luminescence And Corresponding Modification Of Several Rare-Earth Ions Doped Fluoride Materials

In the field of photoluminescence energy conversion materials,rare-earth ions have been widely studied by researchers owing to their special physicochemical properties,such as wide spectrum response,excellent luminescent properties and chemical stability.However,due to the large number of subjects involved in the rare-earth ions doped luminescent materials,the corresponding mechanisms and theories are extraordinarily complicated.Though previous researchers have done a lot of research and exploration,there are still many deficiencies left to be ameliorated.For example,according to spectrum modulation by rare-earth dopant in order to achieve full-band response for solar cell photovoltaic efficiency,there are still some areas of spectral band that lack research;the luminescent properties and efficiency of rare-earth ions have always been influenced by several factors such as host material properties,energy transfer mechanisms and crystal field parameters.In order to explore and solve those problems,based on the materials of fluoride as the theme of this thesis,we synthesized rare-earth ions doped materials and studied their corresponding properties.The main research and results of this thesis are as follows:Firstly,Tm³⁺ions doped YF₃ phosphor was synthesized and the upconversion luminescence was achieved in the infrared region of 1150-1300 nm,which may improve the photovoltaic applications of full solar frequency spectrum.Compared with the conventional Tm³⁺/Yb³⁺ion pairs co-doped system,Tm³⁺ions have been unleashed by Yb³⁺ions,thereby reducing energy loss in the upconversion luminescence process.In addition,the Tm³⁺-sensitized down-conversion luminescence under excitation in ultraviolet region was also studied.Via up-conversion and down-conversion routes,Tm³⁺-sensitized materials could convert both high-energy and low-energy photons to the desired ones which have intense response for silicon solar cells.It is expected that this work will provide a new strategy in extending the application of Tm³⁺ions and enhancing the photovoltaic efficiency of solar cells in the future.Secondly,NaYbF₄ nanocrystals were synthesized through the hydrothermal approach and the corresponding morphologies of nanodisks and nanorods were investigated by the electron microscope.The morphologies were proved to be modified by Gd³⁺ions.Simultaneously,excited at 980 nm,the luminescence of Tm³⁺ions was also modified and enhanced by Gd³⁺ions,implying that the Gd³⁺ions may have a special effect on the optical properties of rare-earth ions doped nanocrystals.Thus,the effect of a single rare-earth sensitizer on the morphologies and luminescent properties of rare-earth doped fluoride nanomaterials was realized.Thirdly,the upconversion luminescence properties of Tm³⁺ions doped ternary fluoride materials are studied.Through the doping of Sr²⁺,Ca²⁺,Mg²⁺ ions of alkaline earth metals,the unit cell parameters of the host materials were modified and the upconversion luminescence intensity of Tm³⁺ions was enhanced.In consideration of the expensive rare-earth raw materials,the cheaper alkaline earth metals will provide a cost-effective path to industrialization manufacture.