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.

/pdf/tests-of-quantum-gravity-from-observations-of-g-ray-bursts-36h2zmgj9a.pdf

Tests of quantum gravity from observations of γ-ray bursts

/pdf/review-of-particle-physics-1996-1997-jeg703df6k.pdf

Review of Particle Physics, 1996-1997

Scintillation photons emitted by LaF3 single crystals doped with Nd3+ have been detected in a multiwire chamber filled with TMAE vapour. This scintillation (λ = 173 nm) is ascribed to a 5d–4f transition of Nd3+ and is characterised by a decay time of 6.3±0.5 ns.

Detection of LaF3:Nd3+ scintillation light in a photosensitive multiwire chamber

The scintillation properties of LaCl3 crystals, doped with Ce3+ concentrations of 0.57, 1.0, 2.0, 4.0, and 10%, are studied under x-ray and γ-quanta excitation at various temperatures. Under x-ray excitation, characteristic doublet Ce3+ emission is observed with a maximum at 3.7 eV. Also self-trapped exciton (STE) emission is observed with a maximum near 3.1 eV. The contribution of STE luminescence to the total light yield decreases with increasing Ce concentration. For LaCl3:0.57%Ce3+, the contribution is 33%, whereas for LaCl3:10%Ce3+ it is 4%. The total light yield of the Ce3+-doped samples ranges from 38 000 photons per megaelectronvolt (ph MeV−1) of absorbed γ-ray energy to 47 000(ph MeV−1) for LaCl3:0.57%Ce3+ and LaCl3:10%Ce3+, respectively. A model is proposed to explain the energy transfer from the host lattice to the Ce3+ ions. At these Ce concentrations, energy transfer by STE diffusion is held to be dominant.

http://iopscience.iop.org/article/10.1088/0953-8984/15/8/319/pdf

The scintillation mechanism in LaCl3:Ce3+

The optical and scintillation properties of pure LuCl3, LuCl3:0.45%, 2%, 4%, 10% Ce3+, LuBr3:0.021%, 0.46%, 0.76%, 2.5%, and 8% Ce3+ are studied under X-ray and γ-ray excitation. The highest light yield of 29,000±3000 photons per MeV (ph/MeV) of absorbed γ-ray energy was measured for LuBr3:0.021% Ce3+. Energy resolutions obtained with a Hamamatsu R1791 photomultiplier tube (PMT) range from 6.0±0.5% to 18±2% for LuBr3:8% Ce3+ and LuCl3:0.45% Ce3+, respectively. For both LuCl3:Ce3+ and LuBr3:Ce3+, binary electron–hole diffusion was proposed as the dominant scintillation mechanism. At lower irradiation temperatures, VK diffusion is probably more important in the case of LuBr3:Ce3+.

Properties and mechanism of scintillation in LuCl3:Ce3+ and LuBr3:Ce3+ crystals

In this study, the authors present Monte Carlo (MC) simulation results for the intensity and angular distribution of scattered radiation from cylindrical absorbers. For coherent scattering the authors have taken into account the effects of interference by using new molecular form factor data for the AAPM plastic materials and water. The form factor data were compiled from X-ray diffraction measurements. The new data have been implemented in the authors' Electron Gamma Shower (EGS4) Monte Carlo system. The hybrid MC simulation results show a significant influence on the intensity and the angular distribution of coherently scattered photons. It is concluded that MC calculations are significantly in error when interference effects are ignored in the model for coherent scattering. Especially for simulation studies of scattered radiation in collimated geometries, where small angle scattering will prevail, the coherent scatter contribution is highly overestimated when conventional form factor data are used.

C.W.E. van Eijk

Papers

Detection of LaF3:Nd3+ scintillation light in a photosensitive multiwire chamber

The scintillation mechanism in LaCl3:Ce3+

Properties and mechanism of scintillation in LuCl3:Ce3+ and LuBr3:Ce3+ crystals

Monte Carlo modeling of coherent scattering: influence of interference

The observation of photon cascade emission in Pr3+-doped compounds under X-ray excitation