Study On Fluorescence Characteristics Of Molybdate Luminescent Materials And Carbon Quantum Dots And Its Application

Since 1996, when white light emitting diode was developed and launched by Nichia Corporation in Japan. The lighting the history of mankind was promoted to a new era, because it have more advantages, such as high luminous efficiency, long life,safety and energy-saving, so it known as the "fourth generation lighting source".However, it`s use in certain lighting occasions was limited due to the lack of red lighting component. In addition, the use of rare earth as luminescent materials let high cost and rare earth chosen simply as a light-emitting substance. Thus, the research of new white light emitting diode emitting material is favored by many scientists. On the basis of previous studies, this paper researched and developed a new type of red phosphor and a new carbon quantum dots fluorescent material, which suitabled for UV excitation, and have been used in the white light emitting diodes. The main content of this paper are as follows:In chapter one, the relevant knowledge that include the principle, implementation and progress of fluorescent material of white light emitting diode was briefly introduced. Among them, the research advances of conventional and novel luminescent material used for white LED light-emitting were reviewed detailly. The aluminate, silicate and nitrogen（oxy） nitride phosphor were mainly reviewed in the section about conventional luminescent material. And the molybdate red phosphor and the novel carbon quantum dots fluorescent material were mainly reviewed in the section about new luminescent material. Finally, the research content and methods were proposed.In chapter two, a series of Eu³⁺doped Lu₂（MoO₄）₃ red phosphors are prepared by solid state reaction method. The crystal structures and luminescent properties are characterized by X-ray diffraction pattern and Photoluminescence spectra,respectively. The Eu³⁺concentration has no influence on Lu₂（MoO₄）₃ crystal structures when the doping concentrations is lower than 0.06. The concentrationquenching phenomenon can be observed when Eu³⁺ doping concentration reaches0.05, which is attributed to energy transfer between Eu³⁺ ions induced by the exchange interaction. The Eu³⁺ doped Lu₂（MoO₄）₃ red phosphors have maximized luminescent intensity when annealed at 1100℃.In chapter three, A series of Eu³⁺ doped（Lu,Gd）_1.95（MoO₄）₃:0.05Eu³⁺ with different Lu/ Gd molar ratio were prepared by solid state reaction method. The crystal structures and luminescent properties were characterized by X-ray diffraction pattern,Photoluminescence spectrum and Attenuation characteristics, respectively. The structure of samples had converted to Gd₂（MoO₄）₃ with tetragonal system from Lu₂（MoO₄）₃（orthogonal structure） when Lu/ Gd molar ratio changed from 1.0: 1.0 to0.4 : 1.6. And with the decrease of Lu/ Gd, Eu³⁺ emission intensity is increased with the Gd³⁺ content enhanced, indicating that Gd³⁺ ions play a role of sensitizing agent in the sample at the emission process. In addition, the average delay lifetime of Eu³⁺ is mutated, due to the crystal structure of the sample changed.In chapter four, the water-soluble fluorescent Carbon dots（C-Dots） with a high luminous efficiency was prepared by hydrothermal method from citric acid（CA） and ethylenediamine（EDA） at 150℃. The surface functional groups, absorption spectra and fluorescence properties of samples were characterized by Fourier transform infrared spectroscopy, UV-vis Spectrophotometry and Fluorescence Spectrometer,respectively. FT-IR results showed that there were a large number of hydrophilic functional groups connecting with the surfaces of C-Dots fluorescent material, and ultraviolet-visible absorption spectrum indicated the presence of two strong absorption peaks at 286 nm and 346 nm which corresponding to n- Ï€ * and Ï€- Ï€ *transition of C=O. A strong peak at 443 nm was found from fluorescence emission spectra when the excitation wavelength is 346 nm, and the half width only 55 nm.Thereby infer that the emitting mechanism of C-Dots fluorescent material is due to the dimensional limitations of light portion in the surface of C-Dots. It was found that the strongest emission peak red shift when the excitation wavelength not less than 380 nm.Analysis indicated that the red shift is due to the uneven particle size or surface functional groups passivation caused by light sites differences in the surface ofC-Dots. It was found Fe³⁺ ions caused largest fluorescence quenching to C-Dots in the experiments of metal ion detection, and the results in line with Stern-Volmer equation.Thus, C-Dots fluorescent material has a unique-high sensitivity detection to Fe³⁺ ions.In chapter five, a new eco-friendly fluorescent film was prepared by R6733 commercially red phosphors and C-Dots, and a white LED was packaged by a "patch" type and ultraviolet LED chip. The transmittance of the fluorescent film is less than20% in ultraviolet region and more than 60% in the visible region. The properties showed the phosphor film can block UV leak, but visible light have big transmittance.It was found that the color coordinates is（0.3255, 0.3587）, and color temperature is about 5900 K of white LED. It sumed that the white LED fluorescent film have more advantages, such as less phosphor, simple preparation process, controled shape and thickness, homogeneous material dispersed, low cost, widely application potential.