Preparation And Properties Of The Inorganic Nanobelt Fluorescent Membranes For WLEDs

In recent years, due to the rapid development of the lighting and display technology, the demands for the fluorescent materials are becoming more and more higher. The packaging of traditional LED lighting and display technology, the phosphor is coated directly on the LEDs chips surface and the heat of the chips will transform to the fluorescent materials directly, which results in the decreasing of conversion efficiency and maturing of the silicone. With the continuous development and improvement of electrospinning technology, it can be used for the preparation of various organic and inorganic fiber membranes with high performance. The inorganic nanofiber fluorescent membrane was prepared by electrospinning, because of the nano-scale and uniform network structure, which has obtained the structure of fluorescence materials before packaging. The membranes fabricated via electrospinning have uniform diameters, a large specific surface area and a large aspect ratio, which contribute to the uniformity of light and lifespan of LED. However, some questions of the inorganic nanofiber fluorescent membrane need to be solved, such as the fluorescence intensity and mechanical properties are not good enough.Oxidation silica based fluorescent material has excellent thermal stability, high quantum efficiency and the rich spectrum. In this paper, a variety of oxidation silica based precursor fiber membranes were prepared by sol-gel and electrospinning methods, and obtained the fluorescent fiber membrane by ammonia gas phase reduction method. The prepared fibrous membranes and packaged LED are characterized by X-ray diffraction(XRD), scanning electronic microscopy(SEM), Photoluminescence spectroscopy(PL), Fourier-infrared spectrometer(FT-IR), Thermogravimetric analyzer(TGA), Instron 5969, Intensified multichannel spectrophotometer(HSP-3000) and etc. for their structure and properties. The research mainly includes the following aspects:The CaSi2O2N2:Eu2+ nanobelt fluorescent membrane for WLED of the remote packaging was prepared by sol-gel combined with electrospinning and the gas-reduction nitridation methods. The micro structure, luminescent and mechanical properties of the nanobelt fluorescent membrane were tested. The obtained sample not only keeps the morphology of nanobelt fiber but also assembles as film with a certain mechanical strength. XRD patterns of sample nitrided at 1250℃ for 4 h were crystallized well and assigned to JCPDF card of the CaSi2O2N2 crystal, and the sample maintained CaSi2O2N2 phase after doping Eu2+ ions. Under ultraviolet excitation(400nm), the emission spectra of Eu2+-doped Ca0.95Si2O2N2 sample consists a board peak near 550 nm, which results from Eu2+ 4f65d→4f7 transition. Based on the far field encapsulation, white LEDs with low correlated color temperature(4832 K), high-color-rendering index(86) and luminous efficacy of 125 lm W-1 were fabricated using the Ca0.95Si2O2N2:Eu0.052+ nanobelt fiber mat and blue chip.The Ca0.68Si9Al3(ON)16:Eu0.1 microbelts mats have been successfully prepared by a versatile and simple electrospinning combining with the gas-reduction nitridation method. As-prepared fiber precursor was uniform and smooth with diameter of 800-900 nm. After removing organic templates and nitridation, the morphology of fiber was well retained and a smooth microbelts phosphor mat was obtained. Through X-ray diffraction(XRD) and Photoluminescence spectroscopy(PL) we can learn that, a pure Ca0.68Si9Al3(ON)16:Eu phase and the highest photoluminescence intensity could be obtained at a relatively low temperature of 1500 oC and Eu2+ doping concentration of 0.1. The microbelts phosphor mat has the bending strength about 4.5 MPa with a external quantum yield as high as 65%. By employing it as yellow phosphor, a high-performance white LED was fabricated with low correlated color temperature(2985K), high-color-rendering index(Ra = 86) and luminous efficacy of 129.5 lm W-1. By employing microbelts phosphor mats with different thicknesses the different color temperatures also could be obtained.The novel flexible SiO2-Based composite belt fluorescent nanofibrous membranes have been successfully prepared by a simple and versatile electrospinning together with gas-reduction nitridation method. As-prepared fiber precursor was smooth and uniform with diameter of 500 nm. After removing organic templates under 500℃ and nitridation, the fiber morphology was well retained and a smooth nanobelt phosphor fiber membrane was obtained. The FNM has high flexibility, it can be laid flat, bent, or rolled without visible damage. The FNM(diameter ~2 cm, thickness ≈ 0.2 mm) is able to withstand the weight of 200 g without breaking. When the strain is 6% by universal material testing machine, the strength of FNM can keep a high value about 6.0 MPa after 500 cycles. The emission spectra of the prepared FNM exhibited a single broad band in the 400-650 nm region, with the maximum intensity always being at 475 nm, and 1000℃ is the best nitridation temperature for the fluorescence intensity of FNM. Moreover, the PL intensity of the free-standing pure inorganic fluorescent nanofibrous membranes have excellent environment, thermal and cycle stability. These results strongly indicated the great potential of pure inorganic fluorescent membranes as the remote packaging materials for LED lighting and soft displaying.