Investigation on Luminescent Glass-ceramics Based on Rare Earth Doped SrO-Al_2O_3-SiO_2 System

Abstract: The semiconductor lighting technology with high-power white LED, has many advantages in energy efficiency, long lifetime, compactness, energy-conservation and environment-protection. The applications of LEDs which having been improved greatly in recent years, are setting foot in the lighting industry and will greatly challenge the conventional lighting.At present, LED devices are mainly packing by LED chips coated on epoxide resin and phosphor powder. There are some deficiencies in their practical application, such as phosphor aging, brightness drop, poor conduct heat of epoxide resin, aging discoloration, shorten life and so on, which brings serious influences on the luminous efficiency and working life of white LED. Therefore, it is urgent to develop novel luminescence materials with improved properties like high color rendering, resistance to high temperature, corrosion and aging. In this paper, we focus on the investigation of glass-ceramics doped with rare earth ions which would be potential fluorescent materials for white LED lighting devices.The Re-doped (Re=Sm3+, Tb3+, Ce3+) SrO-Al2O3-SiO2 (SAS) glass and glass-ceramics with excellent luminescence properties were prepared by composition and heat-treatment designing. The crystallization behavior and luminescent properties of the SAS glass-ceramics were investigated by XRD, SEM and fluorescence spectra.The results indicate that:1. The main crystal phase in this system was monocelsian (SrAl2Si208). The SAS glass-ceramics with suitable crystallization and luminescent properties could be obtained when SrO:Al2O3=10:7 (wt%), and TiO2:ZrO2=3:1(wt%).2. The intensity was more obviously affected by the crystallization temperature than the nucleation temperature. It had been noticed that the luminescent intensities of these glass-ceramics show a tendency of increasing as the crystal size and crystallization ratios increases.3. The Sm3+-doped SAS glass-ceramics could emit green, orange and red lights under the excitation of 405nm long UV or 475nm blue lights. The broad band emissions peaked at 565nm,605nm,650nm and 715nm can be attributed to the 4G5/2→6Hj/2 (j=5,7,9,11) transitions of Sm3+respectively. With the increasing of Sm3+contents, the luminescent intensity of the samples is increased.4. The Tb3+-doped SAS glass-ceramics could emit blue, green, yellow and red lights under the excitation of 376nm UV. The emission band peaked at 489nm,547nm, 588nm and 623nm can be attributed to the 5D4→7Fj(j=6,5,4,3)transitions of Tb3+ respectively. The approximate white light emissions were acquired and got approached to standard illuminant C as the crystallization temperature increases. The white light closest to illuminant C but have a higher colour temperature were acquired when nucleation temperature at 950℃for 3 hours and crystallization temperature at 1150℃for 3 hours.5. The Ce3+-doped SAS glass-ceramics emit red light under blue excitation of 475nm. In addition, it could emit intense blue light at 420nm-480nm under the excitation of broad UV region of 245nm-300nm. With the increase of crystallization temperature and doped concentration, the luminous intensity get stronger. The concentration quenching effect was observed when the content of Ce3+over 0.15mol%.6. The Sm3+/Tb3+co-doped SAS glass-ceramics were excited simultaneously under the excitation of 478nm-485nm and were consist of the characteristic emission spectrum of Sm3+and Tb3+. Enhancement of luminous intensities was observed in Sm3+/Tb3+co-doped glass-ceramics than Sm3+-doped, and the sensitization is due to the energy transfer from Tb3+to Sm3+. The luminescence intensity of Sm3+increases with Tb3+addition. The maximal luminous intensity was achieved with the concentration ratios of Sm3+:Tb3+was 1:1 (mol%). The approximate white light emissions were acquired with Sm+:Tb3+=1:2/1:3 (mol%) and more approached to illuminant C than only Tb3+-doped. The optimal lighting effect was obtained when Sm3+:Tb3+=1:2(mol%) and the chromaticity coordinate was (0.344,0.298). This indicated that the Sm3+/Tb3+co-doped SAS glass-ceramics are potential fluorescent materials for white LED devices…
Key words: Re-doped; SrO-Al_2O_3-SiO_2 glass-ceramics; crystallization; luminescence properties; LED

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