| The white light emitting diodes (LEDs), so called the fourth generation of lightsource, have attracted considerable interests in recent years for their superiorproperties such as stability, high efficiency, saving energy, security, long lifetime,great reliability, non-mercury and environmental friendliness and so on. At present,the phosphor-converted method was recognized as the most common and efficientway to generate white light and this method brought about a new developing space tophosphor. Thus, the phosphor for white light emitting diode has been developedrapidly in recent years and become the research focus in the illumination industry.Since ancient times, skylight has been meeting physiological requirements ofpeople for light and the requirements have grown from original illumination to theoptical art nouveau, which puts forward higher standard that the dynamic naturallighting is simulated and applied to indoor illumination including dynamic andatmosphere. The indoor users not only pay attention to the brightness, but to theinfluence of spectral distribution upon the physiological and mental state of people.The traditional incandescent lamp, gas discharge lamp and energy saving lamp arepoor at tinting and difficult to be used as dynamic illumination source. As the globalenergy crisis and the demanding on environment-protection increase，the w-LEDshave attracted more and more attentions in the lighting market for their kinds ofadvantages, which has been considered as one of the most promising high technologyand the novel solid-state illuminant that the most likely entered the illumination fields.The research and industrialization prospect of w-LEDs have been developed rapidly and internationally in recent years. During the Ninth Five-Year Plan period, theindustrialization of LEDs in China has made tremendous strides funded by the “863”new materials and contracted obviously the gap with international advanced level.Thew-LEDs not only have the potential to substitute for the traditional incandescent lampand energy saving lampbut also can be applied to the background light of notebook,landscaping source, the medical cold light illuminator and combination of solar LED,extensive applications of which were expected for further expansion. With the LEDpreparation technology development and the expanding application, the preparationand performance research on the phosphor of LED have gained more and moreattention. At present, the phosphor-converted w-LEDs have industrialized and it willbring phosphor to greater opportunities and challenges for white light emitting diode.As an important industry material, the metal molybdates have been widelyapplied in photoluminescence, optical fiber, scintillator, microwave devices, humiditysensor, catalyst and so on. Of these, the molybdates of all this were shown to be themost extensively researched with scheelite structure and most of these materials areimportant scintillator or X ray luminous body in practice. In the NaY(MoO4)2host,Molybdic acid (MoO2-4) has special properties and Mo6+is coordinated by fouroxygen atoms in a tetrahedral symmetrical site，which indicates that this compoundshave a high chemical stability. Under the UV-light,(MoO2-4) can show effectiveemission from blue to yellow light and transfer to rare earth ions in the host, whichcan be a good candidate for the red component of white LED. Red chemical methodsuch as hydrothermal method can process at a low temperature and control thecondition of the reaction flexibly. The products by this method with highcrystallization and uniformity need simple equipments to take care of the produces.Thus, this method is the most potential method to synthesize luminescent materials.The high temperature solid state method is simple to be used in laboratory very much.This paper mainly uses the above methods to prepare the samples.The first chapter summarized briefly the advantages, principle ofphotoluminescence of white LEDs, development of rare earth phosphor and thepurpose and significance of the paper. The raw materials, the preparation methods and the characterization techniques of the experiments were introduced in the next chapter.The third chapter studied in detail the phase analysis at different pH value,morphologies, luminescent properties of NaY(MoO3+4)2:Ln(Ln3+=Eu3+, Sm3+, Dy3+)phosphor. The three novel series of samples show the strong sharp lines in the rangeof300-500nm, which is matched well with the blue LED chip or near-UV LED chip.All the emission spectra of the samples are composed of a series of narrow peaksand the strongest spectrum are617nm,575nm,565nm at pH=7, corresponding red,reddish orange and white respectively, which are attributed to the characteristicemissions of rare earth ions. Of course, this means that the phosphorNaY(MoO3+4)2:Ln(Ln3+=Eu3+, Sm3+, Dy3+) can be an excellent candidate forred-emitting phosphor and the single white emitting phosphor. Besides, the densityfunctional theory (DFT) calculations can offer us detailed information about atom andorbital arrangement, which was basically in agreement with the experimental value.The fourth chapter mainly analyzed the luminous mechanism of excitation andemission spectra of the bulk and nanocrystal NaLn(MoO34)2:Eu+(Ln=Gd, Y)materials. Meanwhile, the site-selective excitation and emission spectra have beeninvestigated to make sure the relation of the site of Eu3+to the spectral structures,which is helpful to explore the universal laws of luminescence and realize theregulation of luminescent properties. The fifth chapter concludes the summary of thechapter and introduces the future expectation of this work.Overall, the thesis is devoted to exploring and researching the newhigh-efficiency red phosphor and the single white emitting phosphor based on thecurrent future development of phosphor for w-LEDs, which is not only makecontribution for developing new red phosphor used for white-light-emitting diodes(LEDs), also for a new generation of solid sources and easing the shortage of energy. |
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