Effect Of Microwave Field On Morphology Evolution And Energy Transfer Of A Simultaneous Red And Blue Emission Phosphor For LEDs

With the development of high power phosphor-converted light emitting diodes (pc-LEDs), the performance requirements of fluorescent material have the further improved from the system, components to the size, morphology, crystallinity and materials synthesis. The cage-like structure fluorescent material particles in a suitable size distribution exhibit an distinct enhancement as long as processing parameters can be properly controllled. Meanwhile, microwave (MW) firing procedure has proved to be an very effective means to achieve the desired properties of materials with its advantages of fast-heating rate, volume heating. However, some problems still exhibit in its non-uniformity of heating in volume and MW non-thermal effect particularly in heating solid material.This thesis focuses on a MW effect on morphology of phosphor particle and energy transfer occurring in processing a stoichiometric (Ba,Sr)3MgSi2O8:Eu, Mn phosphor. The achievements that have been made are summarized as follows:A. The cage-like structure and emission enhancement of (Ba,Sr)3MgSi2O8:Eu, Mn phosphor was achieved by optimizing the preparation of precursor and parameter of spray pyrolysis with a feature simultaneous emission at both660nm and430nm.B. The mechanism of morphology evolution of (Ba,Sr)3MgSi2O8:Eu, Mn phosphor involved in MW firing process was understood with the aid of characterization such as DTA/TQ XRD, SEM, diffuse reflectance spectroscopy and PL spectroscopy. It was found that the gas generated owing to the decomposition of nitrates plays the key role in forming cage-like structure. The proper parameter control for forming cage-like structure was optimized in that the gas generation rate, the discharge rate in the sphere particle and diffusion rate of the decomposed oxides are appropriate with each other.C. A grand new view point relevant to MW disturbance on energy transfer in MW heating (Ba,Sr)3MgSi2O8:Eu, Mn was presented by modifying diagrams of energy levels for Eu-Mn ions. Two reasons probably account for the red emission enhancement, i.e. one is the strong paramagnetic effect of Mn2+leading a enhanced energy splitting under microwave magnetic field.The other is that the non-thermal effect of microwave makes the ions occupying the ideal state in the host lattice which promotesthe excitation and emission of rare earth ions so as to enhance the energy transferred to Mn2+and absorbed by Eu2+.In summary, this thesis illustrates the mechanisms on morphology evolution of fluorescent materials and MW disturbance of energy transfer under microwave heating. The results will further the fundamental understanding of MW effect of energy transfer in paramagnetic ion of Mn for red emission, and provide a reference to develop a energy-saving, clean and scaleable MW processing technique for phosphor production.