https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

Phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as an indispensable solid-state light source for the next generation lighting industry and display systems due to their unique properties including but not limited to energy savings, environment-friendliness, small volume, and long persistence. Until now, major challenges in pc-WLEDs have been to achieve high luminous efficacy, high chromatic stability, brilliant color-rending properties, and price competitiveness against fluorescent lamps, which rely critically on the phosphor properties. A comprehensive understanding of the nature and limitations of phosphors and the factors dominating the general trends in pc-WLEDs is of fundamental importance for advancing technological applications. This report aims to provide the most recent advances in the synthesis and application of phosphors for pc-WLEDs with emphasis specifically on: (a) principles to tune the excitation and emission spectra of phosphors: prediction according to crystal field theory, and structural chemistry characteristics (e.g. covalence of chemical bonds, electronegativity, and polarization effects of element); (b) pc-WLEDs with phosphors excited by blue-LED chips: phosphor characteristics, structure, and activated ions (i.e. Ce 3+ and Eu 2+ ), including YAG:Ce, other garnets, non-garnets, sulfides, and (oxy)nitrides; (c) pc-WLEDs with phosphors excited by near ultraviolet LED chips: single-phased white-emitting phosphors (e.g. Eu 2+ –Mn 2+ activated phosphors), red-green-blue phosphors, energy transfer, and mechanisms involved; and (d) new clues for designing novel high-performance phosphors for pc-WLEDs based on available LED chips. Emphasis shall also be placed on the relationships among crystal structure, luminescence properties, and device performances. In addition, applications, challenges and future advances of pc-WLEDs will be discussed.

Phosphors in phosphor-converted white light-emitting diodes: Recent advances in materials, techniques and properties

A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols

The recent confirmation that at least some γ-ray bursts originate at cosmological distances1,2,3,4 suggests that the radiation from them could be used to probe some of the fundamental laws of physics. Here we show that γ-ray bursts will be sensitive to an energy dispersion predicted by some approaches to quantum gravity. Many of the bursts have structure on relatively rapid timescales5, which means that in principle it is possible to look for energy-dependent dispersion of the radiation, manifested in the arrival times of the photons, if several different energy bands are observed simultaneously. A simple estimate indicates that, because of their high energies and distant origin, observations of these bursts should be sensitive to a dispersion scale that is comparable to the Planck energy scale (∼1019 GeV), which is sufficient to test theories of quantum gravity. Such observations are already possible using existing γ-ray burst detectors.

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Tests of quantum gravity from observations of γ-ray bursts

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Review of Particle Physics, 1996-1997

VUV excitation and 1S0 emission of Pr3+ in BaSiF6 and selecting host lattices with 1S0 Pr3+ emission

The scintillation properties of Ba 1− χ La χ F 2+ χ single crystals have been investigated for La concentrations up to about χ = 0.13. The luminescence spectra of the crystals have been recorded during X-ray irradiation. With an XP2020Q photomultiplier and a 137 Cs gamma source, the photoelectron yields of the slow and fast components have been determined. The photoelectron yield of the slow component can be suppressed considerably by doping with La, while the yield of the fast component is hardly affected.

Suppression of the slow scintillation light output of BaF2 crystals by La3+ doping

The scintillation properties of LuI/sub 3/:Ce/sup 3+/(pure, 0.5%, 2%, and 5% Ce/sup 3+/), a new member of the generation of Ce/sup 3+/ doped lanthanide trihalide scintillators, are presented. This material has a calculated density of 5.6 g/cm/sup 3/ and an atomic number Z/sub eff/ of 60.2. Under optical and X-ray excitation, Ce/sup 3+/ emission is observed to peak at 472 and 535 nm. A high light yield of 76 000 photons per MeV (ph/MeV) was measured for LuI/sub 3/:2% Ce/sup 3+/. LuI/sub 3/:Ce/sup 3+/ has a nonexponential decay time. The contribution of short decay components (within 50 ns) to the total light yield is around 50%. An energy resolution (full-width half maximum over peak position) for the 662 keV full energy peak of 4.7/spl plusmn/0.5% was observed for LuI/sub 3/:0.5% Ce/sup 3+/.

Scintillation properties of LuI/sub 3/:Ce/sup 3+/-high light yield scintillators

The optical properties and scintillation mechanism in pure and Ce 31 -doped K2LaX5 and LaX3 have been determined under x-ray, g-ray, vacuum ultraviolet light, and synchrotron radiation excitation. Special attention is paid to the influence of anions X5Cl 2 ,B r 2 , and I 2 , and a comparison is made with properties of pure and Eu 21 -doped KX compounds. The energies of the 5d excited states of Ce 31 have been determined, and the total crystal field splitting and the centroid shift are discussed. An excitation across the band gap creates a combination of self-trapped exciton ~STE! and Ce 31 emission. These emissions are often anticorrelated when temperature or Ce 31 concentration is changed. Their ratio is related to the STE mobility and STE creation rate. Clear trends in the optical properties and scintillation mechanism are observed along the halide series.

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Influence of the anion on the spectroscopy and scintillation mechanism in pure and Ce3+-doped K2LaX5 and LaX3 (X=Cl, Br, I)

The energies of the $5d$ excited states of ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ impurities relative to the conduction band of the insulators ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ and ${\mathrm{Lu}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ were investigated through a temperature and spectrally resolved photoconductivity study. The effective ionization barrier of ${\mathrm{Pr}}^{3+}$ from the $5d$ state to the conduction band is found to be $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ smaller than that of ${\mathrm{Ce}}^{3+}$ in both ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ and ${\mathrm{Lu}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$. The difference is explained by a model, represented by rate equations, that takes into account interconfigurational $4f5d\ensuremath{\rightarrow}4{f}^{2}$ relaxation for ${\mathrm{Pr}}^{3+}$, a process that is absent for ${\mathrm{Ce}}^{3+}$.

C.W.E. van Eijk

Papers

VUV excitation and 1S0 emission of Pr3+ in BaSiF6 and selecting host lattices with 1S0 Pr3+ emission

Suppression of the slow scintillation light output of BaF2 crystals by La3+ doping

Scintillation properties of LuI/sub 3/:Ce/sup 3+/-high light yield scintillators

Influence of the anion on the spectroscopy and scintillation mechanism in pure and Ce3+-doped K2LaX5 and LaX3 (X=Cl, Br, I)

5 d electron delocalization of Ce 3 + and Pr 3 + in Y 2 Si O 5 and Lu 2 Si O 5