Nanodefects in YAG: Ce phosphors

Since the mid-1990s, phosphors have played a key role in emerging solidstate white-lighting technologies that are based on combining a near-UV or blue solid-state light source with downconversion to longer wavelengths. Almost all of them used phosphorescreted a crystalline oxide, nitride, or oxynitride host that is appropriately doped with Gd, Ce or Eu. Activation of phosphors by rare earth elements, leads to the formation of defects in the lattice and due to the change in the luminescent properties. This paper presents the new original model of energy transfer in the YAG crystals, which is a good description of the possible luminescence transitions in crystals. The morphology, spectra and kinetics characteristics of the luminescence of industrial phosphor excited by electron and laser radiation were investigated. The obtained theoretical and practical data are good agreement with each other, and thus are of great interest for understanding the nature of luminescence

Emission properties of YAG: Ce ceramics with barium fluoride flux

In this work, we investigated the luminescent properties of YAG, Ce ceramics with an addition of barium fluoride flux. The ceramic samples were sintered from obtained YAG: Ce, BaF2 phosphor powder. Morphological, luminescent and decay time characteristics of YAG: Ce ceramics were investigated. The luminescence decay kinetics analysis of the ceramics showed that the decay time in phosphors and ceramics is different in the visual spectral range

Nanodefects in YAG:Ce-Based Phosphor Microcrystals

The present paper focused on the study of spectral–kinetic characteristics of luminescence in two batches of yttrium aluminum garnet (YAG):Ce-based phosphors synthesized in different years by two manufacturers: NPO “Platan” in Russia and “GrandLux” in the People’s Republic of China (PRC). Upon studying the structural characteristics of the phosphors—elemental composition, morphology, and X-ray diffraction (XRD) patterns—it was concluded that both types of YAG:Ce phosphors are highly imperfect. The presence of heterogeneities of different nature was accompanied by the introduction—to compensate for charges and elastic stresses—of intrinsic lattice defects during synthesis. There is a high probability of creating complex defects during phosphor synthesis. Luminescence properties (full width at half maximum (FWHM), spectral position of the emission peaks, excitation spectra of emission, emission decay time) are affected by the nearest environment of the luminescence center; whereas the degree of correlation of defects (distance between the components of the donor–acceptor pair) does not depend on the concentration of impurities, intrinsic defects, and their ratio. The results do not fit into the framework of existing ideas regarding the processes in phosphors as systems with widely distributed luminescence centers. The patterns obtained in the paper are discussed based on a hypothesis according to which a nanodefect phosphorus crystal phase is formed during the synthesis

The effect of BaF2 concentration and particle size distribution on the luminescence efficiency of YAG:Ce3+phosphors

Y3Al5O12 (YAG) phosphor powders doped with Ce3+ concentration were synthesized by the solid-state reaction method with different of BaF2 flux concentration. Morphological characterization, photoluminescent properties and decay characteristics of YAG phosphor powders were studied. It was shown that BaF2 directly influenced on particle size distribution of YAG:Ce3+ phosphor. It is necessary to have both large particles agglomerates (size more than 40 μm) and small one (size less than 4 μm) to obtain high energy efficiency in polydisperse YAG:Ce3+ phosphors. It was evidenced, that the effect of both large and small agglomerates on energy efficiency is observed. The luminescence decay time for all investigated samples is significantly different in the spectral range 500 and 700 nm from τ ~ 60 to 80 ns, respectively

Improving "color rendering" of LED lighting for the growth of lettuce

Light plays a vital role on the growth and development of plant. On the base of white light with high color rendering to the benefit of human survival and life, we proposed to improve “color rendering” of LED lighting for accelerating the growth of lettuce. Seven spectral LED lights were adopted to irradiate the lettuces under 150 μmol·m−2·s−1 for a 16 hd−1 photoperiod. The leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared LED light treatments were investigated. We let the absorption spectrum of fresh leaf be the emission spectrum of ideal light and then evaluate the “color rendering” of as-prepared LED lights by the Pearson product-moment correlation coefficient and CIE chromaticity coordinates. Under the irradiation of red-yellow-blue light with high correlation coefficient of 0.587, the dry weights and leaf growth rate are 2-3 times as high as the sharp red-blue light. The optimized LED light for lettuce growth can be presumed to be limited to the angle (about 75°) between the vectors passed through the ideal light in the CIE chromaticity coordinates. These findings open up a new idea to assess and find the optimized LED light for plant growth

Density and microstructural investigation of Ce:YAG ceramic subjected to powerful ultrasonic treatment during the compaction process

The aim of the present work was to investigate the effect of the applied pressure, sintering temperature and ultrasonic treatment during the pressing process on the density and microstructure of translucent ceramics based on yttrium-aluminum garnet doped with cerium ions (Ce: YAG) obtained by conventional sintering of pressed compacts. The optimization of manufacturing conditions of the ceramics was carried out. It was shown that the ultrasonic treatment of initial powder in optimal sintering conditions leads to an increase in the relative density and grain size and decrease in the pore size of the sintered ceramics