Cees Ronda - Academia.edu (original) (raw)

Papers by Cees Ronda

Journal of Solid State Chemistry, Sep 1, 1987

Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Nov 29, 2007

In the present study properties of garnet scintillation ceramics of general composition (Gd, Y)3A... more In the present study properties of garnet scintillation ceramics of general composition (Gd, Y)3Al5O12:Ce3+ have been investigated in a wide temperature range, from 80 to 570K. Measurements of the luminescence intensity and decay time temperature dependencies have been performed under X-ray and photo excitation. It is shown that luminescence intensity rises during heating up to room temperature and then starts falling due to thermal ionization of electrons from Ce3+ excited states to the conduction band. Values of activation energy of the thermal ionization process have been obtained from decay time measurements. Processes responsible for the rise of luminescence intensity are considered.

Technical Physics Letters, Oct 1, 2015

A pulsed X-ray source has been designed and constructed with the following parameters: X-ray tube... more 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 pulse has a rectangular shape with a relative amplitude instability below 0.8%. In combination with appropriate detection system, the proposed X-ray source allows the kinetics of X-ray-induced luminescence growth and decay to be measured in a six-decimal-order dynamic range with respect to time and amplitude. Examples of X-ray-induced luminescence kinetics measured in scintillators are presented.

ECS Journal of Solid State Science and Technology

This paper provides examples of a strategy employed to improve specific properties of phosphors a... more This paper provides examples of a strategy employed to improve specific properties of phosphors and scintillators which would otherwise have limited their performance in lighting, cathode-ray tubes, and medical imaging technologies. When electron-hole pairs are produced by the exposure to high-energy radiation, the activator ion in the lattice preferentially captures one of the charge carriers. The subsequent capture of the carrier of opposite charge yields the activator ion luminescence. The carrier of the opposite charge can also be diverted to defects in the lattice. The trapping by defects reduces the brightness of phosphors and is responsible for the unwanted afterglow in scintillators. The strategy that is adopted to suppress the trapping by defects is to deliberately introduce an impurity ion that can compete successfully with the defects for the charge carrier. Since the impurity ion traps charge of the opposite sign to the activator ion, we label them as “anti-activators.” ...

Optical Materials: X, 2021

Crystal Growth & Design, 2020

Garnet scintillators often suffer from undesired afterglow, the origin of which is not always wel... more Garnet scintillators often suffer from undesired afterglow, the origin of which is not always well-understood. A possible origin is contamination with transition metal (TM) ions. These impurities can act as traps giving rise to afterglow. Alternatively, they may show long lived (ms) d-d emission. Here we present a systematic study on the role of 3d TM impurities in (Lu,Gd) 3 (Ga , Al) 5 O 12 garnet scintillators. Scintillator disks intentionally doped with ppm levels of Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn were studied to identify TM-related traps in thermoluminescence (TSL) glow curves and their role in afterglow. For Ti, V and Cr additional TSL peaks were observed that gave rise to RT afterglow in the 10-2-10 3 s time range, depending on garnet composition. On the ms time scale long lived red/near infrared emission was observed from Mn and Fe impurities, explained by spin-forbidden d-d emission. We show that afterglow can be reduced by the use of ultrapure raw materials. Other solutions include bandgap engineering for the garnet host to modify trap depths and applying optical filters to block the spin-forbidden d-d emission. The present study provides an insightful overview of the role of 3d TM impurities on afterglow in Ce-doped scintillators and procedures to predict and reduce afterglow. These insights will aid the development of Ce-doped garnets with superior afterglow behavior.

The Journal of Physical Chemistry C, 2019

Journal of Luminescence, 2019

The shift of the conduction band (CB) edge for thirty different (Lu,Gd) 3 (Ga,Al) 5 O 12 :Ce comp... more 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-related peak positions (in temperature and trap depth) with composition modification was investigated as well. In Gdcontaining (Lu,Gd) 3 (Ga,Al) 5 O 12 compositions a non-monotonous shift of the CB edge with increasing Ga content has been affirmed. The difference between thermal trap depths evaluated from our TSL experiments and optical trap depths obtained from the literature was explained by the role of lattice relaxation. Highlights • Connection of Ta, Cr, Yb, Ti and Eu impurities to specific TSL peaks for Lu 1 Gd 2 Ga 3 Al 2 O 12 :Ce • Dependence Yb-related TSL peak position as function of (Lu,Gd) 3 (Ga,Al) 5 O 12 :Ce composition • Observation non-monotonous shift of the CB edge for (Lu,Gd) 3 (Ga,Al) 5 O 12 :Ce with increasing Ga content • Systematic difference of 0.5 eV between optical (literature) and thermal trap depths, rationalized using a simple model

The Journal of Physical Chemistry A, 2019

Afterglow is an important phenomenon in luminescent materials and can be desired (e.g. persistent... more 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 approach for the description of the time-dependent afterglow from TSL glow curves using a model with a distribution of trap depths. The method is based on the deconvolution of the energy dependent density of occupied traps derived from TSL glow 1 curves using Tikhonov regularization. To test the validity of this new approach, the procedure is applied to experimental TSL and afterglow data for Lu 1 Gd 2 Ga 3 Al 2 O 12 :Ce ceramics co-doped with 40 ppm of Yb 3+ or Eu 3+ traps. The experimentally measured afterglow curves are compared with simulations based on models with and without the continuous trap depth distribution. The analysis clearly demonstrates the presence of a distribution of trap depths and shows that the new approach gives a more accurate description of the experimentally observed afterglow. The new method will be especially useful in understanding and reducing undesired afterglow in scintillators.

Technical Physics Letters, 2017

The curves of thermally stimulated luminescence of Gd 3 Ga 3 Al 2 O 12 :Ce 3+ ceramics (a nominal... more The curves of thermally stimulated luminescence of Gd 3 Ga 3 Al 2 O 12 :Ce 3+ 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 bandgap of Gd 3 Ga 3 Al 2 O 12 is presented.

Optical Materials, 2017

Due to presence of charge carrier traps, many scintillating materials exhibit afterglow. The de-t... more 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 factor in an unambiguous manner by connecting TSL and afterglow measurements. In order to accomplish that, we have devised a special method of extracting the lifetime of trapped carriers from afterglow measurements, independent of kinetic order. The procedures are first shown on simulated TSL and afterglow curves and then illustrated using (Y,Gd) 3 Al 5 O 12 :Ce garnets as example.

ECS Journal of Solid State Science and Technology, 2015

Building and Environment, 2017

Indoor VOCs still remain at high levels in many areas, which may directly impact human health. In... more Indoor VOCs still remain at high levels in many areas, which may directly impact human health. In this study, hundreds of residential indoor air samples were collected in Xi'an and Hangzhou from April 2014 to November 2015. Indoor VOC pollution level of newly renovated residences was more serious than that of old residences (approximately 10 to 15 times). The mean indoor VOC level of newly renovated residences in Xi'an was 0.882±1.922 mg/m 3 , similar to Hangzhou's levels (0.862±1.394 mg/m 3). But part of the benzene homologues concentrations in Hangzhou were higher than those in Xi'an, and the exposure risk in Hangzhou could be 1.5 to 8 times that in Xi'an. This study aims to identify characteristics of indoor VOC pollution, quantitatively estimate the combined effects of temperature and humidity, and reveal sink mechanism associated with indoor VOCs. The results indicate that indoor VOC pollution in newly renovated residences is mainly affected by the combination of temperature and humidity as sink effect, especially for the components with large Henry's Law Constant. The results of this study also provide valuable guidance on indoor VOC pollution control, i.e., humidity control is a countermeasure to reduce potential indoor air pollution for people who live in humid areas.

Журнал технической физики, 2017

В диапазоне температур от 80 до 550 K измерены кривые термостимулированной люминесценции керамик ... more В диапазоне температур от 80 до 550 K измерены кривые термостимулированной люминесценции керамик Gd3Ga3Al2O12:Ce3+: 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 уровней редкоземельных ионов в запрещенной зоне Gd3Ga3Al2O12. DOI: 10.21883/PJTF.2017.09.44577.16604

Physical Review B, 2017

Paramagnetic Ce 3+ optical emitters have been studied by means of optically detected magnetic res... more Paramagnetic Ce 3+ optical emitters have been studied by means of optically detected magnetic resonance (ODMR) via Ce 3+ 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 intensity of photoluminescence excited by circularly polarized light into Ce 3+ absorption bands can be used for selective monitoring the population of the Ce 3+ ground-state spin sublevels. Direct evidence of the cross-relaxation effects in garnet crystals containing two electron spin systems, i.e., the simplest one of Ce 3+ ions with the effective spin S = 1 2 and the system of Gd 3+ ions with the maximum spin S = 7 2 , has been demonstrated. Magnetic resonance of Gd 3+ has been found by monitoring Ce 3+ emission in cerium-doped garnet crystals with gadolinium concentrations of 0.1 at. %, 4%-8%, and 100%, which implies the impact of the Gd 3+ spin polarization on the optical properties of Ce 3+. Strong internal magnetic fields in superparamagnetic crystals were shown to modify the processes of recombination between UV-radiation-induced electron and hole centers that lead to the recombination-induced Ce 3+ emission. Observation of spikes and subsequent decay in the cross-relaxation-induced ODMR signals under pulsed microwave excitation is suggested to be an informative method to investigate transient processes in the many-spin system of Ce 3+ , Gd 3+ , and electron and hole radiation-induced centers.

Applied Magnetic Resonance, 2016

Electron paramagnetic resonance (EPR) in the ground state of Gd3+ ions in (LuGd)3 Al5O12 single c... more 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 allowed monitoring the populations of the Ce3+ ground-state spin sublevels, which can be changed at the EPR of Gd3+ due to Gd–Ce cross relaxation.