Microstructure And Luminescent Properties Of Down-conversion Glass For Light-Emitting Diodes

Known as the next-generation lighting source, solid-state lighting （SSL） is evaluated asthe third revolution of the lighting industry, following the introduction of incandescent bulbsand fluorescent lamps. SSL has been applied in a broader range of applications, such asgeneral illumination, backlighting, traffic signals, medical treatment, agriculture, waterpurification and imaging. Over the past decade, great advances in solid-state lightingtechnologies have been made, especially in white light-emitting diodes （LED） by usingphosphors as wavelength converters. Phosphor materials are involved in multidisciplinaryfields of materials science, crystal chemistry, inorganic chemistry, solid-state chemistry,solid-state physics, optics, crystal field theory, and computational materials science. In this M.S thesis, a variety of luminescence glasses for wavelength conversion are investigated, andthe important achievements obtained are summarized as follows:A. Without any reducing atmosphere, parts of Eu³⁺ions added as Eu₂O₃were reduced toEu²⁺ions during the preparation process of borosilicate glasses. The mixed valence of Eu²⁺and Eu³⁺was identified by photoluminescence spectrum and electron paramagnetic resonance（EPR）. The ratio of Eu²⁺/Eu³⁺can be effectively adjusted by changing the compositionB2O3/BaO ratios of glasses.B. The specific valence state of Eu is ascribed to the unequivalent substitution andde-polymerization network of the as-prepared borosilicate glasses. With the increase ofalkaline-earth metals oxide, the free oxygen will destroy the bridge oxygen structure togenerate more non-bridging oxygen. The variation of Eu²⁺/Eu³⁺ratio in glasses is attributed tothe site shift of Ba²⁺ion with increasing content of BaO in glass samples as synthesized in theair. The de-polymerization network also makes the full width at half maximum （FWHM） tobe broadened for excitation and emission spectrum.C. Eu³⁺-doped borosilicate glass was observed to be excited efficiently by 394, 466 and534 nm light. The emission intensity increases with the increase of Eu³⁺concentration up to 8mol% then subjected to quecnheing at higher concentrations. The color rendering index （CRI）has been increased upon covering this converting glass to LED. Through further optimizationof composition, structure and combination, the Eu-doped borosilicate glass is a promising redflourescent material to enhance red emission.D. The Eu²⁺, Mn²⁺co-doped borosilicate glass could be excited efficiently by 350 nm,two emission bands exist in emission spectrum. Blue light emission originates from a typicalemission of Eu²⁺ion, and the red emission is from the 4T-6A transition of Mn²⁺owing to theEu²⁺- Mn²⁺resonance energy transfer. The emission intensity reaches a maxmumium whenthe Eu²⁺concentration gets to be around 0.2 mol%, and the blue/red ratios changes distinctlyby adjusting the Mn²⁺concentration.