Cees Ronda

• Prof. Dr.
• Managing Director at Philips

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The performance of scintillator materials and phosphors for x-ray imaging is adversely affected by afterglow, giving rise to ghost images and thus compromising image quality. Here, the afterglow of the well-known computed tomography (CT) phosphor Gd2O2S:Pr is investigated with time-delayed afterglow spectroscopy. It is shown that these afterglow sp...

Scintillators based on Ce-doped garnets are regularly co-doped with Mg²⁺ or Ca²⁺ to form Ce ions in 4+ state and reduce undesired afterglow. However overly high Ce⁴⁺ concentration leads to poor light yield performance. In order to understand the reason for variation in luminescence efficiency of Ce³⁺- and Ce⁴⁺-doped garnets we investigate the diffe...

This article outlines the main results of a research and development cooperation between Philips Research Eindhoven; Peter the Great St. Petersburg Polytechnic University; Ioffe Institute, St. Petersburg; Utrecht University; and Philips Healthcare. It reviews the properties of garnet ceramics in the (Lu,Gd) <sub xmlns:mml="http://www.w3.org/1998/Ma...

Light yield, time response, afterglow and thermoluminescence of Ce-doped garnet scintillators and persistent luminescent materials are controlled by a complex interplay between recombination and trapping/detrapping processes. Extensive research has contributed to a good qualitative understanding of how traps, impurities and the presence of Ce⁴⁺ aff...

The shift of the conduction band (CB) edge for thirty different (Lu,Gd) 3 (Ga,Al) 5 O 12 :Ce compositions, with simultaneous variation in Lu/Gd and Ga/Al content was studied using thermally stimulated luminescence (TSL). Specific TSL peaks were related to impurities of Ta, Cr, Yb, Ti and Eu in Lu 1 Gd 2 Ga 3 Al 2 O 12 :Ce ceramics. The shift of Yb-...

Afterglow is an important phenomenon in luminescent materials and can be desired (e.g. persistent phosphors) or undesired (e.g. scintillators). Understanding and predicting afterglow is often based on analysis of thermally stimulated luminescence (TSL) glow curves assuming the presence of one or more discrete trap states. Here we present a new appr...

The presence of aluminum and gallium isotopes with large nuclear magnetic and quadrupole moments in the nearest environment of impurity ions Mn²⁺ and Ce³⁺ in garnets made it possible to use hyperfine and quadrupole interactions with these ions to determine the spatial distribution of the unpaired electron and the gradient of the electric field at t...

Cerium-doped mixed oxide garnets are promising luminescent materials to use as LED phosphors or scintillators for radiation detectors. In this paper, temperature-dependent characteristics of Ce-doped multicomponent garnets ceramics have been studied under photo and X-ray excitation. Ceramic samples of Y <sub xmlns:mml="http://www.w3.org/1998/Math/M...

In this article, a high level overview is given of the factors that determine the emission properties of luminescent materials doped with rare-earth ions, followed by elucidating how tuning of the emission properties can be used to optimize the performance of devices in which they are applied.

Due to presence of charge carrier traps, many scintillating materials exhibit afterglow. The de-trapping mechanisms are usually studied separately via either thermally stimulated luminescence (TSL) or isothermal decay (afterglow) measurements. In this paper, we develop procedures to determine trap parameters such as thermal trap depth and frequency...

Paramagnetic Ce3+optical emitters have been studied by means of optically detected magnetic resonance (ODMR) via Ce3+ spin-dependent emission in cerium-doped garnet crystals which were both gadolinium free and contain gadolinium in a concentration from the lowest (0.1%) to 100%, i.e., to the superparamagnetic state. It has been shown that the inten...

The primary emphasis of this research was to investigate the foundations of phthalate (PAEs) pollutant source researches and then firstly confirmed the concept of the coefficient of volatile strength, namely phthalate total content in per unit mass and unit surface area of pollutant sources. Through surveying and evaluating the coefficient of volat...

The curves of thermally stimulated luminescence of Gd3Ga3Al2O12:Ce³⁺ ceramics (a nominally pure sample and samples doped with rare-earth ions) are measured in the temperature range of 80–550 K. The depth and the frequency factor of electron traps established by Eu and Yb impurities are determined. An energy-level diagram of rare-earth ions in the b...

We report the results of the investigation of Ga-doping effects on the electronic structure of the yttrium-aluminum garnet (YAG). The bandgap structure was studied both experimentally using thermally stimulated luminescence (TSL) technique and theoretically by first-principles density functional theory (DFT) calculations. We observe the non-linear...

В диапазоне температур от 80 до 550 K измерены кривые термостимулированной люминесценции керамик Gd 3 Ga 3 Al 2 O 12 :Ce ³⁺ : номинально чистого образца и образцов, активированных рядом редкоземельных ионов. Определены глубина залегания и частотный фактор электронных ловушек, обусловленных примесями Eu и Yb. Представлена энергетическая диаграмма ур...

Pulsed electron paramagnetic resonance (EPR) and pulsed electron-nuclear double resonance (ENDOR) techniques have been applied to study the environment of luminescent Ce3+ ions in garnet based scintillator powders and ceramics. The presence of aluminum and gallium isotopes with large nuclear magnetic and quadrupole moments in the nearest neighborho...

Luminescent nanopowders of single (Y3Al5O12:Ce³⁺) and multicomponent (Lu2Gd1Al5O12:Ce³⁺) garnets were synthesized by the solvothermal method in a high pressure autoclave. The synthesis conditions were optimized with respect to morphological and photoluminescence properties. Optimized conditions allow to synthesize well-dispersed nanoparticles with...

The invention relates to an UV radiation device, comprising an LED comprising a nitridic material which is arranged to emit first UV radiation in a wavelength range of 200 nm-300 nm and a luminescent material doped with at least one of the following activators selected out of the group Eu2+, Ce3+, Pr3+, Nd3+, Gd3+, Tm3+, Sb3+, Tl+, Pb2+ and Bi3+, w...

Electron paramagnetic resonance (EPR) in the ground state of Gd3+ ions in (LuGd)3 Al5O12 single crystals has been found by monitoring the Ce3+ photoluminescence intensity under circularly polarized excitation in the presence of the 35 GHz microwave field. Due to spin selection rules for optical transitions, the circularly polarized excitation allow...

Shallow and deep electronic traps in various mixed oxide garnet ceramics (Y,Lu,Gd)3(Al,Ga)5O12 have been studied by thermally stimulated luminescence spectroscopy in the 80 – 550 K temperature range. It is shown that the substitution of Al ions by Ga and Y by Gd or Lu in YAG:Ce affects the properties of the traps. It is established that the studied...

The moisture sensitivity of LuI3:Ce,Hf and luminescent properties of undoped LuI3 and LuI3:M (M=Ce3+, Tb3+, Dy3+) powders were investigated. The possibility of improving the air and moisture stability of LuI3:Ce by Hf doped was tested. It was proven that the Hf contribution to the LuI3:Ce stability is very limited and is insignificant to render LuI...

In this paper, we will review recent developments in scintillators, with a focus on scintillating materials for application in Computed Tomography (CT) and Positron Emission Tomography (PET).Main emphasis in the paper is on the translation of device requirements into material properties that need to be obtained. We will do this in particular to imp...

A pulsed X-ray source has been designed and constructed with the following parameters: X-ray tube voltage, 10–50 kV; anode current, up to 2 A; pulse duration (smooth control), 80 ns–2 μs; and leading and trailing front width, 6 ns. The source can operate in both single-pulse and pulse-train mode with a repetition frequency of up to 2 kHz. The X-ray...

A giant magnetic field effect on spin-dependent recombination of the radiation-induced defects has been found in cerium doped gadolinium based garnet crystals and ceramics, promising materials for scintillator applications. A sharp and strong increase in the afterglow intensity stimulated by external magnetic field and an evidence of the magnetic f...

The spectral and kinetic characteristics of YAG:Ce,Tb powders (with Tb3+ concentration varying up to 100%, relative to Y) using cathode-ray and UV excitations were determined. The energy diagram of YAG:Ce,Tb was constructed and energy transfer processes in the compound were studied. The most effective resonance energy transfer takes place at Tb3+ c...

The luminescence properties of Eu2+ doped strontium aluminates are reported and reviewed for a variety of aluminates, viz. SrAl12O19, SrAl4O7, Sr4Al14O25, SrAl2O4 and Sr3Al2O6. The aim of the research is to investigate the role of local coordination and covalency of the aluminate host lattice, related to the Sr/Al ratio, on the optical properties o...

A tungstate-based scintillating material and a method for using a tungstate-based scintillating material is provided. In addition, a radiation detector and an imaging device incorporating a tungstate-based scintillating material are provided.

The photoluminescence and time resolved emission for Eu2+ in Sr4Al14O25 has been investigated in the temperature range 4 to 500 K. The Eu2+ emission changes in a peculiar way with temperature. At low temperature two emission band are observed at 490 and 425 nm which are attributed to emission from Eu2+ on the 7- and 10-coordinated site. Upon raisin...

In this paper, a number of different application fields of inorganic luminescent materials are being discussed. In a tutorial manner, it will be shown how device requirements are being translated into properties the luminescent materials need to have. To this end many different material properties that have a strong influence on the device performa...

The optical properties of Gadolinium Gallium Aluminum Garnet, Gd3(Ga,Al)5O12, doped with Ce3+ are investigated as a function of the Ga/Al ratio, aiming at an improved understanding of the energy flow and luminescence quenching in these materials. A decrease of both the crystal field strength and band gap with increasing content of Ga3+ is observed...

The Dorenbos relation is an empirical model that relates the position of the lowest fd level of any lanthanide ion with that of Ce3+ in the same host lattice. The relation is widely used to estimate the energy of fd levels of trivalent lanthanide ions in a given host lattice based on the peak position of the lowest fd level of at least one of the l...

Lu3Al5O12:Ce3+ (LuAG:Ce) is a scintillator with a fast response time. The light yield is lower than theoretically expected and to increase the light yield co-doping with Pr3+ is investigated. To better understand the energy flow to the Ce3+ ion, first low temperature emission and excitation spectra of Pr3+ doped LuAG were investigated, allowing the...

The d-f emission from Ce3+ and Pr3+ in garnets is attracting considerable attention, especially in relation to application in white light LEDs and scintillators. An important aspect is the luminescence quenching temperature TQ. It is not trivial to determine TQ and to unravel the quenching mechanism. In this paper the TQ of d-f emission for Ce3+ an...

This paper reports the photoluminescence and afterglow of Sr2SiO4 doped with Eu2+ and Dy3+. Factors governing the formation of the monoclinic or orthorhombic phase of this ortho-silicate are described and the impact of the crystallographic modification on the luminescence and afterglow under UV and VUV excitation are discussed and insight in factor...

Single phase Ca3Sc2Si3O12 co-doped with Pr3+ and Mg2+ was synthesized by high temperature solid state reaction. The optical spectroscopy of this composition was investigated using time-resolved VUV spectroscopy upon excitation with synchrotron radiation. It was demonstrated that the addition of Mg2+ leads to a significant modification of the lumine...

Lu(3)Al(5)O(12) (LuAG) doped with Ce(3+) is a promising scintillator material with a high density and a fast response time. The light output under X-ray or γ-ray excitation is, however, well below the theoretical limit. In this paper the influence of codoping with Tb(3+) is investigated with the aim to increase the light output. High resolution spe...

Luminescent solar concentrators would allow for high concentration if losses by reabsorption and escape could be minimized. We introduce a phosphor with close-to-optimal luminescent properties and hardly any reabsorption. A problem for use in a luminescent concentrator is the large scattering of this material; we discuss possible solutions for this...

The present invention provides a method of monitoring per formance of a discharge lamp. The discharge lamp includes electrodes and a discharge vessel filled with gas and equipped with a luminescent layer, wherein the gas is intended to emit a first ultraviolet light in a first spectral range when the gas is excited by an electric field produced by...

The invention relates to a light emitting device (1) with high colour rendering comprising a wavelength converting mem ber (2) with a luminescent medium for wavelength conver sion of blue light and/or ultraviolet light (10) into red light and/or yellow and/or green light and a light Source (3) emit ting blue light (10) and/or ultraviolet light arra...

During the last decade, afterglow phosphors have attracted considerable attention due to their potential applications in various fields, including emergency lighting, special light sources, graphic arts, or optical data storage. Recently, research on persistent luminescent phosphors has been shifted to rare earth ion doped aluminates and silicates...

The invention relates to a colar cell system for extraterrestrial use comprising a converter with an inorganic converter material adapted to match extraterrestrial conditions.

The document was not made available for publication as part of the conference proceedings.

The paper presents the synthetic procedure and the structural characterisation of Pr3+-doped eulytite double phosphates Sr3La(PO4)3 and Ba3Lu(PO4)3. The luminescence properties of these materials were studied employing time-resolved VUV spectroscopy upon excitation with synchrotron radiation. The 5d–4f emission of Pr3+ ions was detected and assigne...

The local structure of the Ce3+ ion in the yellow emitting YAG:Ce phosphor has been studied by Extended X-ray Absorption Fine Structure spectroscopy in the 20–300K temperature range. It is shown that the dopant Ce3+ replaces Y3+ in the garnet structure, giving rise to a significant expansion of the distorted cubic local structure, limited to the ne...

In a Luminescent Solar Concentrator (LSC), short-wavelength light is converted by a luminescent material into longwavelength light, which is guided towards a photovoltaic cell. In principle, an LSC allows for high concentration, but in practice this is prevented by loss mechanisms like limited sunlight absorption, limited quantum efficiency and hig...

During last decade, afterglow phosphors have attracted considerable attention due to their potential applications in various fields, including safety indication, light sources, luminous paint or optical data storage. In recent years, research on persistent luminescent phosphors has shifted towards rare earth ions doped into aluminates or silicates....

A tanning device is described that includes semiconductor light-emitting diodes (LEDs) as a light source, which LEDs are preferably composed of (InGa)N, (AlGa)N, (AlInGa)N or (AlInGa)P as their semiconductor material.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The silicates Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12, both undoped and doped with Pr3+ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown ef...

This chapter deals with inorganic luminescent materials and consists of two parts. It starts with a general description of luminescence- and excitation mechanisms, by giving a description of the way they operate in well-known devices, like lamps or medical imaging equipment. In the second part, we concentrate on emerging medical applications. The f...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Almost a century of research on luminescent materials has resulted in a very good understanding of luminescence mechanisms, and as a result many luminescent materials have been developed which operate at physical limits in terms of energy—or quantum efficiency. Mechanisms limiting phosphor performance have been studied as well and many factors redu...

The optical properties of SrSi2AlO2N3 doped with Eu2+ and Yb2+ are investigated towards their applicability in LEDs. The Eu2+-doped material shows emission in the green, peaking around 500nm. The emission is ascribed to the 4f65d1–4f7 transition on Eu2+. In view of the too low quantum efficiency and the considerable thermal quenching of the emissio...

In recent years afterglow phosphors have attracted considerable attention due to their potential applications in various fields, including emergency signs, light sources, luminous paint or optical data storage [1]. At the beginning of the 20th century the ZnS:Cu phosphor were developed as long afterglow pigments. In the past several years, research...

Yttrium aluminum garnet (YAG) doped with Ce3+ is the phosphor of choice for the conversion of blue to yellow light in the rapidly expanding market of white light LEDs, but it is generally thought to suffer from a low luminescence quenching temperature. The luminescence quenching temperature is an important parameter, especially in high-power LEDs,...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Ultra fast scintillators are of high interest for positron emission tomography (PET) to enhance time and spatial resolution, which improves the quality of medical imaging [1]. This work deals with the preparation and characterisation of Pr3+ doped UV emitting scintillators, since the Pr3+ ion frequently shows an emission spectrum in the UV range, w...

Ultra fast scintillators are of high interest for positron emission tomography (PET) to enhance time and spatial resolution, which improves the quality of medical imaging [1]. This work deals with the preparation and characterisation of Pr3+ doped UV emitting scintillators, since the Pr3+ ion frequently shows an emission spectrum in the UV range, w...

The garnet Ca3Sc2Si3O12 (CSSO) and the silico-carnotite Ca3Y2Si3O12 (CYSO) and Ca3Lu2Si3O12 (CLSO) materials, both undoped and doped with Pr3+, have been synthesized by solid state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchro...

Color point tuning is an important challenge for improving white light LEDs. In this paper, the possibilities of color tuning with the efficient LED phosphor Sr1−x−y−zCaxBaySi2O2N2:Euz2+ (0 ≤ x, y ≤ 1; 0.005 ≤ z ≤ 0.16) are investigated. The emission color can be tuned in two ways: by changing Eu2+ concentration and by substitution of the host latt...

Optical imaging using unspecific contrast agents as well as targeted and disease-specific agents play a vital role in preclinical research. Moreover, optical imaging is on the verge of establishing itself as a clinically relevant imaging modality. Also in-vitro diagnostical procedures rely to a large degree on optical labels to report disease-speci...

Ultra fast scintillator are of high interest for positron emission tomographs (PETs) to enhance time and space resolution, which improves the quality of medical imaging [1]. This work deals with the preparation and characterisation of Pr3+ doped UV emitting scintillators, since the Pr3+ ion shows an emission spectrum in the UV range, which is due t...

This work deals with the preparation and characterisation of Pr3+ doped UV emitting scintillators. Pr3+ ions frequently show an emission spectrum in the UV range, which is due to allowed optical transitions. These are interconfigurational transitions between the lowest crystal-field component of the [Xe]4f15d1 configuration and the lowest energy le...

The invention relates to nanoparticles coated with an inorganic nanoscale material herein referred to as core-shell nanoparticle, in which the core material has a wider band gap than the shell material. The described core-shell nanoparticles are very suitable for the application in photodynamic therapy due to their enhanced energy transfer abilit

This paper describes an investigation towards very fast emitting oxidic luminescent materials doped with Pr3+. Such materials have the potential to be applied as scintillators in Positron Emission Tomography.

The garnet Ca3Sc2Si3O12 (CSSO) and the silico-carnotite Ca3Y2Si3O12 (CYSO) and Ca3Lu2Si3O12 (CLSO) materials, both undoped and doped with Pr3+, have been synthesized by solid state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchro...

In this, the only up-to-date book on this key technology, the number-one expert in the field perfectly blends academic knowledge and industrial applications. Adopting a didactical approach, Professor Ronda discusses all the underlying principles, such that both researchers as well as beginners in the field will profit from this book. The focus is o...

Introduction Optical Properties of Quantum DotsParticle in a One-dimensional Potential WellParticle in Three-dimensional Potentials Particle in a General Three-dimensional PotentialElectron in a Coulomb PotentialThe Hydrogen AtomDensity of States in Low-dimensional StructuresElectrons, Holes, and ExcitonsLow-dimensional Structures The Weak Confinem...

In this paper, we will outline how new requirements have revitalised research on luminescent materials. Using selected examples from applications in lighting and the medical field, we will show how materials science on luminescent materials results in new and improved phosphors.

The optical properties of SrSi2O2N2 doped with divalent Eu2+ and Yb2+ are investigated. The Eu2+ doped material shows efficient green emission peaking at around 540nm that is consistent with 4f7→4f65d transitions of Eu2+. Due to the high quantum yield (90%) and high quenching temperature (>500K) of luminescence, SrSi2O2N2:Eu2+ is a promising materi...