Preparation And Properties Of Oxide And Oxynitride Fibrous Membranes For LEDs

With the development of electronic science and technology, lighting-emitting diodes (LEDs)have been widely applied to photoelectron and lighting engineering fields. In the traditionalpackaging methods, the phosphor is coated directly on the LEDs chips surface and the heat of thechips will transform to the fluorescent materials directly, which results in the decreasing ofconversion efficiency and maturing of the silicone. Therefore, the membranes with controllablenetwork structure and uniform diameters will be a promising material for LED packaging. In thepast decades, electrospinning has been proved to be a simple and versatile but potential process togenerate highly oriented fibers from a wide range of polymers. The membranes fabricated viaelectrospinning have uniform diameters, a large specific surface area and a large aspect ratio,which contribute to the uniformity of light.In this paper, the flexible oxide and oxynitride fluorescent fibrous membranes are prepared tosolve the problems such as the clusters of phosphor and the low strength of inorganic fibrousmembranes. The prepared fibrous membranes are characterized by scanning electronicmicroscopy (SEM), X-ray diffraction (XRD), Fourier-infrared spectrometer (FT-IR), UV-VISspectrometer (UV-VIS), Photoluminescence spectroscopy (PL) and etc. for their structure andproperties.The research mainly includes the following aspects:Eu3+doped SiO2fibrous membranes are prepared by sol-gel and electrospinning methods.The morphology of samples can be controlled by adjusting the concerntration of PVA, the voltage,the injection speed and the receive distance The diameters of the obtained precursor membranesare between800~900nm. After the heating treatment, the diameters of the Eu3+doped SiO2fibrous membranes decrease, but the surface of the fibers retains smooth and uniform. Bycontrolling the heating rate, the Eu3+doped SiO2fibrous membranes present the relatively hightensile strength (4.31MPa), which exhibits no cracks after bending and recovering process. Byexcited at392.6nm, the emission peaks between570~670nm are observed, which attribute to the5D0→7FJtransition. The PL spectra also show that the luminescence intensity attains the highest value at the concentration of8mol%Eu3+doped and750℃heating treatment.The Tb3+doped SiO2fibrous membranes are prepared by so-gel and electrospinning methods.By controlling the heating rate, the organic components can be removed slowly and themorphology remains uniform and smooth without any cracks. The diameters of the Tb3+dopedSiO2fibrous membranes were between600~700nm. The obtained samples not only keep themicromorphology of nanofiber but also assemble as a film macroscopically. By excited at375nm,the strongest emission peak at544.2nm is observed, which attributes to the5D0→7F5transition.The PL spectra also show that the luminescence intensity attains the highest value at theconcentration of9mol%Tb3+doped and750℃heating treatment. The controllable networkstructure and uniform diameters of the Tb3+doped SiO2fibrous membranes contribute to theconsistent spatial distribution and high transmittance. By pasting the free-standing membranes onthe LED chips, a remote packaged method is employed. The light homogeneity and efficacy ofLEDs packaged by fibrous membranes are improved.The Eu2+doped oxide and oxyntride fibrous membranes are prepared by electrospinning andammonia gas phase reduction methods. The mixed phases of SiO2and CaSiO3are obtained after1300℃nitridation, and then the Si2N2O following. After the nitridation at1400℃for2h, thedesired Si3N4and CaSi2O2N2fibers are obtained with porous structure. As the nitridationtemperature increasing, the red-shift is observed in emission spectra by doping N into the host.Meanwhile, the peak-broaden is observed in the excitation spectra, which shows the advantages inthe application with the UV-LED chips.