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Special Issue "Techniques and Methods for Advanced Characterization of Luminescent Materials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 15 February 2018

Special Issue Editors

Guest Editor
Prof. Dr. Hubertus T. Hintzen

Group Luminescent Materials, Section Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, The Netherlands
Website | E-Mail
Interests: nitride; phosphor; luminescence; optical properties
Guest Editor
Dr. Benjamin Dierre

Group Luminescent Materials, Section Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, The Netherlands
Website | E-Mail
Interests: characterization; luminescence; oxynitrides; nanostructures; energy- and environment-related applications

Special Issue Information

Dear Colleagues,

For a long time, luminescent materials (such as organic or rare-earth/transition metal-doped inorganic phosphors, semiconductors, nanoclusters or quantum dots), have been important in our daily life because of their use in traditional applications in consumer products (lighting, displays) and professional equipment (medical imaging, X-ray computed tomography). Nevertheless, novel luminescent materials with improved or unprecedented properties are still being discovered, and new applications are continuously being developed in the field of energy (solar cells, photo-catalysis), health (biomarkers, disinfection), mobility (smart highway) or security (emergency lighting, currency protection). A continued progress in the performance of luminescent materials and their applications is dependent on a deep understanding of the relationships between their luminescence properties on the one hand and their chemical composition and structure on the other. For such purposes, a detailed characterization of luminescent materials is required, not only with standard approaches but also more and more with sophisticated techniques and methods. Therefore this Special Issue aims at reviewing the latest developments in advanced characterization of luminescent materials, with sophisticated experimental techniques (such as neutron diffraction, combination of electron-beam based techniques, single-particle approaches, EXAFS, XANES, Solid State NMR, Mössbauer spectroscopy, positron annihilation) as well as sophisticated theoretical methods (such as first principles crystal and electronic structure calculations). Papers reviewing state-of-the-art as well as original papers on promising new developments are welcome contributions for this Special Issue of Materials, in order to show that the future of luminescent materials may be even brighter than their rich past.

Prof. Dr. Hubertus T. Hintzen
Dr. Benjamin Dierre
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • luminescent material
  • phosphor
  • luminescence
  • spectroscopy
  • characterization
  • advanced techniques

Published Papers (8 papers)

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Research

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Open AccessFeature PaperArticle Time-Resolved Photoluminescence Microscopy for the Analysis of Semiconductor-Based Paint Layers
Materials 2017, 10(11), 1335; doi:10.3390/ma10111335
Received: 29 September 2017 / Revised: 9 November 2017 / Accepted: 18 November 2017 / Published: 21 November 2017
Cited by 1 | PDF Full-text (8828 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In conservation, science semiconductors occur as the constituent matter of the so-called semiconductor pigments, produced following the Industrial Revolution and extensively used by modern painters. With recent research highlighting the occurrence of various degradation phenomena in semiconductor paints, it is clear that their
[...] Read more.
In conservation, science semiconductors occur as the constituent matter of the so-called semiconductor pigments, produced following the Industrial Revolution and extensively used by modern painters. With recent research highlighting the occurrence of various degradation phenomena in semiconductor paints, it is clear that their detection by conventional optical fluorescence imaging and microscopy is limited by the complexity of historical painting materials. Here, we illustrate and prove the capabilities of time-resolved photoluminescence (TRPL) microscopy, equipped with both spectral and lifetime sensitivity at timescales ranging from nanoseconds to hundreds of microseconds, for the analysis of cross-sections of paint layers made of luminescent semiconductor pigments. The method is sensitive to heterogeneities within micro-samples and provides valuable information for the interpretation of the nature of the emissions in samples. A case study is presented on micro samples from a painting by Henri Matisse and serves to demonstrate how TRPL can be used to identify the semiconductor pigments zinc white and cadmium yellow, and to inform future investigations of the degradation of a cadmium yellow paint. Full article
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Open AccessArticle Study on Scattering and Absorption Properties of Quantum-Dot-Converted Elements for Light-Emitting Diodes Using Finite-Difference Time-Domain Method
Materials 2017, 10(11), 1264; doi:10.3390/ma10111264
Received: 31 August 2017 / Revised: 6 October 2017 / Accepted: 30 October 2017 / Published: 3 November 2017
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Abstract
CdSe/ZnS quantum-dot-converted elements (QDCEs) are good candidates for substituting rare-earth phosphor-converted elements (PCEs) in white light-emitting diodes (LEDs); however, studies on their scattering and absorption properties are scarce, suppressing further increment in the optical and thermal performance of quantum-dot-converted LEDs. Therefore, we introduce
[...] Read more.
CdSe/ZnS quantum-dot-converted elements (QDCEs) are good candidates for substituting rare-earth phosphor-converted elements (PCEs) in white light-emitting diodes (LEDs); however, studies on their scattering and absorption properties are scarce, suppressing further increment in the optical and thermal performance of quantum-dot-converted LEDs. Therefore, we introduce the finite-difference time-domain (FDTD) method to achieve the critical optical parameters of QDCEs when used in white LEDs; their scattering cross-section (coefficient), absorption cross-section (coefficient), and scattering phase distributions are presented and compared with those of traditional YAG phosphor-converted elements (PCEs) at varying particle size and concentration. At a commonly used concentration ( < 50 mg / cm 3 ), QDCEs exhibit stronger absorption (tens of millimeters, even for green-to-red-wavelength light) and weaker scattering ( < 1 mm 1 ) compared to PCEs; the reabsorption, total internal reflection, angular uniformity, and thermal quenching would be more significant concerns for QDCEs. Therefore, the unique scattering and absorption properties of QDCEs should be considered when used in white LEDs. Furthermore, knowledge of these important optical parameters is helpful for beginning a theoretical study on quantum-dot-converted LEDs according to the ray tracing method. Full article
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Open AccessArticle Transition of Emission Colours as a Consequence of Heat-Treatment of Carbon Coated Ce3+-Doped YAG Phosphors
Materials 2017, 10(10), 1180; doi:10.3390/ma10101180
Received: 30 July 2017 / Revised: 12 October 2017 / Accepted: 12 October 2017 / Published: 16 October 2017
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Abstract
To modify the luminescence properties of Ce3+-doped Y3Al5O12 (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N2 atmosphere. Luminescence of the carbon
[...] Read more.
To modify the luminescence properties of Ce3+-doped Y3Al5O12 (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N2 atmosphere. Luminescence of the carbon coated YAG:Ce3+ phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce3+ is the highest when heated at 1650 °C, while a blue emission at 400–420 nm is observed when heated at 1500 °C but not at 1650 °C. It is verified by X-ray diffraction (XRD) that the intriguing luminescence changes are induced by the formation of new phases in C@YAG:Ce3+-1500 °C, which disappear in C@YAG:Ce3+-1650 °C. In order to understand the mechanisms responsible for the enhancement of YAG:Ce3+ emission and the presence of the blue emission observed for C@YAG:Ce3+-1500 °C, the samples have been investigated by a combination of several electron microscopy techniques, such as HRTEM, SEM-CL, and SEM-EDS. This local and cross-sectional analysis clearly reveals a gradual transformation of phase and morphology in heated C@YAG:Ce3+ phosphors, which is related to a reaction between C and YAG:Ce3+ in N2 atmosphere. Through reaction between the carbon layer and YAG host materials, the emission colour of the phosphors can be modified from yellow, white, and then back to yellow under UV excitation as a function of heat-treatment in N2 atmosphere. Full article
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Open AccessArticle Counting the Photons: Determining the Absolute Storage Capacity of Persistent Phosphors
Materials 2017, 10(8), 867; doi:10.3390/ma10080867
Received: 29 June 2017 / Revised: 16 July 2017 / Accepted: 24 July 2017 / Published: 28 July 2017
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Abstract
The performance of a persistent phosphor is often determined by comparing luminance decay curves, expressed in cd/m2. However, these photometric units do not enable a straightforward, objective comparison between different phosphors in terms of the total number of emitted photons, as
[...] Read more.
The performance of a persistent phosphor is often determined by comparing luminance decay curves, expressed in cd/m 2 . However, these photometric units do not enable a straightforward, objective comparison between different phosphors in terms of the total number of emitted photons, as these units are dependent on the emission spectrum of the phosphor. This may lead to incorrect conclusions regarding the storage capacity of the phosphor. An alternative and convenient technique of characterizing the performance of a phosphor was developed on the basis of the absolute storage capacity of phosphors. In this technique, the phosphor is incorporated in a transparent polymer and the measured afterglow is converted into an absolute number of emitted photons, effectively quantifying the amount of energy that can be stored in the material. This method was applied to the benchmark phosphor SrAl 2 O 4 :Eu,Dy and to the nano-sized phosphor CaS:Eu. The results indicated that only a fraction of the Eu ions (around 1.6% in the case of SrAl 2 O 4 :Eu,Dy) participated in the energy storage process, which is in line with earlier reports based on X-ray absorption spectroscopy. These findings imply that there is still a significant margin for improving the storage capacity of persistent phosphors. Full article
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Open AccessArticle A Photoluminescence Study of the Changes Induced in the Zinc White Pigment by Formation of Zinc Complexes
Materials 2017, 10(4), 340; doi:10.3390/ma10040340
Received: 22 February 2017 / Revised: 15 March 2017 / Accepted: 21 March 2017 / Published: 25 March 2017
Cited by 1 | PDF Full-text (1489 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
It is known that oil paintings containing zinc white are subject to rapid degradation. This is caused by the interaction between the active groups of binder and the metal ions of the pigment, which gives rise to the formation of new zinc complexes
[...] Read more.
It is known that oil paintings containing zinc white are subject to rapid degradation. This is caused by the interaction between the active groups of binder and the metal ions of the pigment, which gives rise to the formation of new zinc complexes (metal soaps). Ongoing studies on zinc white paints have been limited to the chemical mechanisms that lead to the formation of zinc complexes. On the contrary, little is known of the photo-physical changes induced in the zinc oxide crystal structure following this interaction. Time-resolved photoluminescence spectroscopy has been applied to follow modifications in the luminescent zinc white pigment when mixed with binder. Significant changes in trap state photoluminescence emissions have been detected: the enhancement of a blue emission combined with a change of the decay kinetic of the well-known green emission. Complementary data from molecular analysis of paints using Fourier transform infrared spectroscopy confirms the formation of zinc carboxylates and corroborates the mechanism for zinc complexes formation. We support the hypothesis that zinc ions migrate into binder creating novel vacancies, affecting the photoluminescence intensity and lifetime properties of zinc oxide. Here, we further demonstrate the advantages of a time-resolved photoluminescence approach for studying defects in semiconductor pigments. Full article
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Open AccessArticle New Developments in Cathodoluminescence Spectroscopy for the Study of Luminescent Materials
Materials 2017, 10(3), 312; doi:10.3390/ma10030312
Received: 22 January 2017 / Revised: 7 March 2017 / Accepted: 15 March 2017 / Published: 17 March 2017
Cited by 2 | PDF Full-text (4578 KB) | HTML Full-text | XML Full-text
Abstract
Herein, we describe three advanced techniques for cathodoluminescence (CL) spectroscopy that have recently been developed in our laboratories. The first is a new method to accurately determine the CL-efficiency of thin layers of phosphor powders. When a wide band phosphor with a band
[...] Read more.
Herein, we describe three advanced techniques for cathodoluminescence (CL) spectroscopy that have recently been developed in our laboratories. The first is a new method to accurately determine the CL-efficiency of thin layers of phosphor powders. When a wide band phosphor with a band gap (Eg > 5 eV) is bombarded with electrons, charging of the phosphor particles will occur, which eventually leads to erroneous results in the determination of the luminous efficacy. To overcome this problem of charging, a comparison method has been developed, which enables accurate measurement of the current density of the electron beam. The study of CL from phosphor specimens in a scanning electron microscope (SEM) is the second subject to be treated. A detailed description of a measuring method to determine the overall decay time of single phosphor crystals in a SEM without beam blanking is presented. The third technique is based on the unique combination of microscopy and spectrometry in the transmission electron microscope (TEM) of Brunel University London (UK). This combination enables the recording of CL-spectra of nanometre-sized specimens and determining spatial variations in CL emission across individual particles by superimposing the scanning TEM and CL-images. Full article
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Review

Jump to: Research

Open AccessFeature PaperReview Thermoluminescence as a Research Tool to Investigate Luminescence Mechanisms
Materials 2017, 10(12), 1357; doi:10.3390/ma10121357
Received: 27 September 2017 / Revised: 22 November 2017 / Accepted: 23 November 2017 / Published: 26 November 2017
PDF Full-text (4223 KB) | HTML Full-text | XML Full-text
Abstract
Thermally stimulated luminescence (TSL) is known as a technique used in radiation dosimetry and dating. However, since the luminescence is very sensitive to the defects in a solid, it can also be used in material research. In this review, it is shown how
[...] Read more.
Thermally stimulated luminescence (TSL) is known as a technique used in radiation dosimetry and dating. However, since the luminescence is very sensitive to the defects in a solid, it can also be used in material research. In this review, it is shown how TSL can be used as a research tool to investigate luminescent characteristics and underlying luminescent mechanisms. First, some basic characteristics and a theoretical background of the phenomenon are given. Next, methods and difficulties in extracting trapping parameters are addressed. Then, the instrumentation needed to measure the luminescence, both as a function of temperature and wavelength, is described. Finally, a series of very diverse examples is given to illustrate how TSL has been used in the determination of energy levels of defects, in the research of persistent luminescence phosphors, and in phenomena like band gap engineering, tunnelling, photosynthesis, and thermal quenching. It is concluded that in the field of luminescence spectroscopy, thermally stimulated luminescence has proven to be an experimental technique with unique properties to study defects in solids. Full article
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Open AccessFeature PaperReview Surface Sensitive Techniques for Advanced Characterization of Luminescent Materials
Materials 2017, 10(8), 906; doi:10.3390/ma10080906
Received: 25 May 2017 / Revised: 25 July 2017 / Accepted: 1 August 2017 / Published: 4 August 2017
Cited by 1 | PDF Full-text (9951 KB) | HTML Full-text | XML Full-text
Abstract
The important role of surface sensitive characterization techniques such as Auger electron spectroscopy (AES), X-ray photo electron spectroscopy (XPS), time of flight scanning ion mass spectrometry (TOF-SIMS) and High resolution transmission electron microscopy (HRTEM) for the characterization of different phosphor materials is discussed
[...] Read more.
The important role of surface sensitive characterization techniques such as Auger electron spectroscopy (AES), X-ray photo electron spectroscopy (XPS), time of flight scanning ion mass spectrometry (TOF-SIMS) and High resolution transmission electron microscopy (HRTEM) for the characterization of different phosphor materials is discussed in this short review by giving selective examples from previous obtained results. AES is used to monitor surface reactions during electron bombardment and also to determine the elemental composition of the surfaces of the materials, while XPS and TOF-SIMS are used for determining the surface chemical composition and valence state of the dopants. The role of XPS to determine the presence of defects in the phosphor matrix is also stated with the different examples. The role of HRTEM in combination with Energy dispersive spectroscopy (EDS) for nanoparticle characterization is also pointed out. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: New developments in cathodoluminescence spectroscopy for the study of luminescent materials
Authors: Daniel den Engelsen, George R. Fern, Paul G. Harris, Terry G. Ireland, Jack Silver
Affiliation: Centre for Phosphor and Display Materials, Wolfson Centre for Materials Processing, Brunel University London, Uxbridge, Middlesex, UB8 3PH, UK
Abstract: Cathodoluminescence (CL) spectroscopy has long been a widely used tool for the study of luminescent electronic materials: phosphors, semiconductors and nano-structured devices [1–5]. Apart from recording spectra it can also be used to probe electronic properties on a nanometre scale with an electron beam in a scanning electron microscope (SEM). In this article three innovations, of which two refer to the combination of CL spectroscopy and microscopy in a SEM, for studying phosphors that have been recently developed in our laboratory will be reviewed [6–9].
The first is a new method to determine the CL-efficiency of thin layers of phosphor powders. When the inorganic phosphor to be investigated is a wide band phosphor with a band gap (Eg) > 5 eV, charging of the phosphor particles will occur upon bombardment with electrons. To overcome this problem of charging a comparison method has been developed [6,7].
The study of CL of luminescent material with a SEM is the second subject to be treated [8]. In ordinary SEMs that are equipped with a photon detector, e.g. a photo multiplier tube (PMT), the panchromatic image of the (luminescent) specimen can reveal features that cannot be observed with the secondary electron detectors of the SEM. A detailed description to determine the decay time of phosphor materials in a SEM without a beam blanking device is presented.
Finally is the combination of microscopy and spectrometry in a transmission electron microscope (TEM) will be presented [9,10]. The JEOL TEM of Brunel University was, when it was delivered, a unique instrument being equipped with a VulcanTM CL detector of Gatan (USA) for imaging (panchromatic) and spectroscopic purposes. This combination of microscopic and spectroscopic techniques enabled the recording of CL-spectra of nanometre-sized specimens and determining spatial differences in one crystal by superimposing the STEM and light images.
In the paper the principles of the three measuring methods and some examples of use will be presented and discussed.

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