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

Thermal population of the 4f 1 5d 1 state in BaSO 4 :Pr 3¿

Luminescence of Ce3+ ions in alkaline earth borophosphates

A thermal neutron image plate (IP) consisting of a mixture of BaFBr : Eu 2+ and Gd2O3 (IP-Gd) is compared with an alternative plate consisting of M 2 B 5 O 9 X : Eu 2+ ( M = Ca , Sr , Ba ; X = Cl,Br ) (IP-B). In particular, the Detective Quantum Efficiency (DQE) of both plates is considered. Monte Carlo simulations of the energy deposition process after the absorption of a neutron show that the variance of the energy deposition in the IP-Gd affects the DQE to a large extent. Because of this, the average number of photoelectrons detected per incident neutron, 〈Nphe〉, has to be only 1.3 for the haloborates to obtain an IP-B with a higher DQE value than the maximum possible with a IP-Gd.

The feasibility of boron containing phosphors in thermal neutron image plates, in particular the systems M2B5O9X : Eu2+ (M=Ca, Sr, Ba; X=Cl, Br). Part I: simulation of the energy deposition process

In this study basic effects are investigated of ion-host interactions on 4f-5d excitations of Ce 3+ ions in wideband ionic host compounds. Particularly the shift of the average 4f-5d transition energy compared to that of the free ion, the centroid shift, is of interest. The self-induced dipole effect where the 4f or 5d electron dynamically polarizes the neighboring ions is analyzed in detail. Taking into account the overlap of the 5d orbital of Ce 3+ with the neighbor anions, the standard classical expression was modified, and the result is that this not only drastically reduces the value of the polarization contribution to the centroid shift but also the steep dependence on the distance to the anions almost vanishes. This polarization effect and the additional contributions such as covalency and dynamic correlation should be included in a configuration interaction CI calculation applied on a cluster of ions around the Ce 3+ ion. Calculations with Hartree-Fock Moller-Plesset perturbation theory corrected to second order for perturbation effects and coupled-cluster theory with single, double, and triple excitations were conducted with various basis sets and cluster sizes and it turned out that the results do not include the polarization effect and so this contribution had to be calculated separately and was added to the CI results. Good agreement at the 0.15 eV level is obtained between theory and experiment for Ce 3+ in BaF2, LaAlO3, and LaCl3.

/pdf/ab-initio-calculation-of-the-contribution-from-anion-dipole-2aff6oc5bq.pdf

Ab initio calculation of the contribution from anion dipole polarization and dynamic correlation to 4f-5d excitations of Ce3+ in ionic compounds

The neutron back scattering technique may be used to search for low-metallic land mines. An advantage of this technique is the speed of detection: the scanning speed may be made comparable to that of a metal detector. The method is sensitive to soil moisture. A limitation of the method is therefore that the soil must be sufficiently dry. The neutrons are produced with a pulsed neutron generator. An image of the back scattered thermal neutron radiation is obtained with a two dimensional position sensitive detector. Getting optimal settings for the detector system is described. The mine detection time as function of the neutron pulse parameters is investigated. Results with various dummy mines are presented

/pdf/land-mine-detection-with-neutron-back-scattering-imaging-2dbro5t8qr.pdf

C.W.E. van Eijk

Papers

Thermal population of the 4f 1 5d 1 state in BaSO 4 :Pr 3¿

Luminescence of Ce3+ ions in alkaline earth borophosphates

The feasibility of boron containing phosphors in thermal neutron image plates, in particular the systems M2B5O9X : Eu2+ (M=Ca, Sr, Ba; X=Cl, Br). Part I: simulation of the energy deposition process

Ab initio calculation of the contribution from anion dipole polarization and dynamic correlation to 4f-5d excitations of Ce3+ in ionic compounds

Land mine detection with neutron back scattering imaging using a neutron generator