The Lu2.98Ce0.01Y0.01Al5O12 and Y2.99Ce0.01Al5O12 phosphors were synthesized by solid state reaction at temperature 1623 K and pressure 1.5 × 107 Pa in (95% N2 + 5% H2) atmosphere. Under the conditions, the compounds crystallize in the form of isolated euhedral partly faceted microcrystals ∼19 μm in size. The crystal structures of the Lu2.98Ce0.01Y0.01Al5O12 and Y2.99Ce0.01Al5O12 garnets have been obtained by Rietveld analysis. The photoluminescence (PL) and X-ray excited luminescence (XL) spectra obtained at room temperature indicate broad asymmetric bands with maxima near 519 and 540 nm for Y2.99Ce0.01Al5O12 and Lu2.98Ce0.01Y0.01Al5O12, respectively. The light source was fabricated using the powder Lu2.98Ce0.01Y0.01Al5O12 phosphor and commercial blue-emitting n-UV LED chips (λex = 450 nm). It is found that the CIE chromaticity coordinates are (x = 0.388, y = 0.563) with the warm white light emission correlated color temperature (CCT) of 6400 K and good luminous efficiency of 110 lm/W.

Pressure-stimulated synthesis and luminescence properties of microcrystalline (Lu,Y)3Al5O12:Ce3+ garnet phosphors

The optical properties of YAG:Ce phosphor were measured by a double-integrating-sphere system and calculated by Mie theory and Monte Carlo ray tracing to provide precise optical characterizations of YAG:Ce phosphor for white light-emitting diode (LED) packaging design. Measurement results showed that the phosphor presents strong absorption for blue light, high reflection for yellow light, and an isotropic emission pattern of converted light. The conversion efficiency and quantum efficiency for the saturated phosphor are around 70% and 87%, respectively. Based on the measurement results, the absorption coefficient, scattering coefficient, and anisotropy factor of the phosphor calculated by Mie theory were compared with those calculated by ray-tracing simulation to modify Mie theory to find a reasonable method that can easily obtain the optical constants of YAG:Ce phosphor. Comparisons revealed that Mie theory can predict the variation of the optical constants of phosphor, but the absorption and scattering cross sections should be multiplied with two fitting parameters. The fitting parameters have been given in this study and can be obtained by testing packaged LEDs with different phosphor concentrations.

Measurement and numerical studies of optical properties of YAG:Ce phosphor for white light-emitting diode packaging

Synthesis of YAG:Ce phosphor via different aluminum sources and precipitation processes

Infrared laser stimulated broadband white emission of Yb3+:YAG nanoceramics

Abstract Worldwide commercial interest in the production of cerium doped yttrium aluminium garnet (YAG:Ce) phosphors is reflected in the widespread use of white light emitting devices. Despite of the fact that YAG:Ce is considered a “cool phosphor” it is the most important in white LED technology. This article reviews the developed techniques for producing phosphors with superior photoluminescence efficiency, including solid-state reaction, sol-gel and (co)precipitation methods. Also, by co-doping with rare earth elements, a red/blue shift is reached in the spectrum. The characteristics of YAG:Ce phosphors are investigated because the properties of the phosphors are strongly influenced by the synthesis routes and the sintering temperature treatment. After the phase analysis, morphology and emission studies of the phosphors there may be seen the conditions when the transition from the amorphous phase to the crystalline phase appears, when luminescent properties are influenced by the crystalline form, purity, average size of the particles, co-doping and so on.

https://www.degruyter.com/downloadpdf/j/oere.2015.23.issue-4/oere-2015-0038/oere-2015-0038.xml

Synthesis and characterization of YAG:Ce phosphors for white LEDs

Changes of optical properties of cerium doped YAG single crystals (0.05, 0.1, 0.2 at. % Ce, and 0.2 at. % Ce + 0.1 at. % Mg) after thermal annealing at 1400°C in air or 1200°C in N 2 +H 2 mixture and subsequent γ or proton irradiation were investigated. For initial Ce 3+ contents 0,05 at. % a decrease of the final Ce 3+ concentration was observed. Appropriate changes in luminescence of Ce: YAG crystals were observed as a consequence of dopant concentration changes. They were small after γ-irradiation of Ce: YAG crystals with Ce 3+ content >0,05at.% and reached about 100% after γ-irradiation of crystals with Ce 3+ content <0.05 at. %.

http://www.researchgate.net/profile/Slawomir_Kaczmarek/publication/239071319_Changes_in_Optical_Properties_of_Ce_YAG_Crystals_under_Annealing_and_Irradiation_Processing/links/00b49523c88ac92445000000.pdf

Changes in Optical Properties of Ce: YAG Crystals under Annealing and Irradiation Processing

Absorption and additional absorption of LiNbO 3 crystals doped with Cr 3+ during growth or by diffusion process were investigated before and after γ-irradiation with a dose of 10 5 Gy and also before and after proton irradiation with a fluency of 10 14 cm -2 . It was found that chromium ions may be mtroduced into LiNbO 3 crystals also as Cr 2+ . ESR measurements of Cr:LiNbO 3 crystals irradiated by γ-rays and electrons were performed. Paramagnetic peak after γ and electron irradiation was observed, which vanishes after annealing at 400°C for 3h both in optical and ESR spectra. Mn 2+ lines were also observed, which diminish after electron irradiation only.

Radiation defects in LiNbO3 single crystals doped with Cr3+ ions

Valency change of Cr, Fe, Cu, Er, Ce dopants inside oxide compounds under proton irradiation

Changes in optical properties of some oxide compounds (YAG, YAG:Nd 3+ , YAG:Ce 3+ , YAG:Ce 3+ ,Mg 2+ , YAG:Cr 3+ , YAG:Cr 4+ , SrLaGa3O7:Dy 3+ , SrLaGa3O7:Cr 3+ , SrGdGa3O7:Cr 3+ , LiNbO3:Cr 3+ and LiNbO3:Cu 2+ ) induced by 21 MeV proton irradiation were studied. In the optical absorption spectra lines which belong to optically active dopants (like Ce 3+ , Cr 3+ , Fe 3+ ) and F-type color centers are seen. Influence of proton irradiation on such centers is observed. It seems to be attributed to the ionization and/or recombination of definite centers. Moreover, for relatively high proton fluencies, Frenkel defects are probably created.

Interaction of protons with oxide compounds

-y and electron as grown crystals were used while for proton irradiations the crystals were thermally annealed. For small concentrations of cerium ions (u 0.01 at.%) an increase in the lumi- nescence (about 100%) was observed after gamma irradiation with a dose of 10 5 Gy. This increase was due to the growth in Ce 3 + ions concentration after γ-irradiation (= 50%), due to the Ce 4 + -> Ce 3reaction. For highly doped Ce:YAG crystals (0.1 at%, 0.2 at.%) also an increase, but much smaller (4%), for the Mg codoped crystals (0.1 at.%) was observed. After 1 MeV electron irradiation in the over-threshold type interaction a de- crease in luminescence is observed due to the domination of the Ce3+ -> C e4+ ionization process. In the case of the proton irradiation, for small fluencies (Pe. 10 13 particles/cm 2 ) an increase in luminescence is observed due to the domination of the recharging processes of Ce

/pdf/changes-in-luminescence-of-ce-yag-crystals-under-ionizing-42kr98djph.pdf

J. Wojtkowska

Papers

Changes in Optical Properties of Ce: YAG Crystals under Annealing and Irradiation Processing

Radiation defects in LiNbO3 single crystals doped with Cr3+ ions

Valency change of Cr, Fe, Cu, Er, Ce dopants inside oxide compounds under proton irradiation

Interaction of protons with oxide compounds

CHANGES IN LUMINESCENCE OF Ce:YAG CRYSTALS UNDER IONIZING RADIATION TREATMENT*