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Special Issue "Luminescent Materials 2017"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Energy Materials".

Deadline for manuscript submissions: closed (31 October 2017)

Special Issue Editors

Guest Editor
Dr. Jonathan Kitchen

Chemistry, University of Southampton, Southampton, SO17 1BJ, UK
Website | E-Mail
Guest Editor
Dr. Robert Elmes

Department of Chemistry, Maynooth University, National University of Ireland, Maynooth, Ireland
Website | E-Mail

Special Issue Information

Dear Colleagues,

Luminescent materials have continued to attract the interest of researchers over the past decade, and with many important technological applications for everyday life, the field shows no signs of slowing down.

Applications for luminescent materials traverse the traditional chemical and biological sciences where examples include light emitting technology (LEDs/OLEDs), bio-markers for diagnostics, sensor technologies, solar cells, logic gates/molecular electronics, and cellular imaging agents to name just a few. Similarly, the systems used to create luminescent materials have been constructed using a diverse range of luminophores that include those based purely on organic systems, those based on emissive metals (transition metals and lanthanides) and hybrid mixtures of both. Moreover, luminescent materials can take many forms and, over the past few years there have been many excellent examples reported in the literature including soft materials (e.g., micelles and colloids), nano-particles (e.g., surface functionalised AuNPs), polymers (e.g., biodegradable polymeric biomaterials), gels (e.g., supramolecular organo- and hydro-gels), quantum dots, thin films (e.g., Langmuir-Blodgett monolayers), clays, 2D and 3D network materials (e.g., MOFs/COFs, ordered layered materials), as well as others.

With this Special Issue we aim to highlight some new advances in the field of luminescent materials, from fundamentals aspects through to application and future directions for the field.  We would like to take this opportunity to invite contributions from experts in the field where we welcome both original research papers, as well as review articles.

Dr. Jonathan A. Kitchen
Dr. Robert Elmes
Guest Editors

Manuscript Submission Information

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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 materials
  • Supramolecular Materials
  • Photoluminescence
  • Electroluminescence
  • Chemiluminescence
  • Lanthanides
  • Bio-markers
  • Cellular Imaging
  • Soft-materials
  • Polymers
  • Gels
  • Sensors
  • Up-conversion
  • Quantum Dots
  • Thin Films
  • Nano-particles

Published Papers (11 papers)

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Research

Jump to: Review

Open AccessArticle Tuning the Photoluminescence of Graphene Quantum Dots by Photochemical Doping with Nitrogen
Materials 2017, 10(11), 1328; doi:10.3390/ma10111328
Received: 28 September 2017 / Revised: 31 October 2017 / Accepted: 14 November 2017 / Published: 20 November 2017
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Abstract
Nitrogen-doped graphene quantum dots (NGQDs) were synthesized by irradiating graphene quantum dots (GQDs) in an NH3 atmosphere. The photoluminescence (PL) properties of the GQDs and the NGQDs samples were investigated. Compared with GQDs, a clear PL blue-shift of NGQDs could be achieved
[...] Read more.
Nitrogen-doped graphene quantum dots (NGQDs) were synthesized by irradiating graphene quantum dots (GQDs) in an NH3 atmosphere. The photoluminescence (PL) properties of the GQDs and the NGQDs samples were investigated. Compared with GQDs, a clear PL blue-shift of NGQDs could be achieved by regulating the irradiating time. The NGQDs obtained by irradiation of GQDs for 70 min had a high N content of 15.34 at % and a PL blue-shift of about 47 nm. This may be due to the fact that photochemical doping of GQDs with nitrogen can significantly enhance the contents of pyridine-like nitrogen, and also effectively decrease the contents of oxygen functional groups of NGQDs, thus leading to the observed obvious PL blue-shift. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Co-Precipitation Synthesis and Optical Properties of Mn4+-Doped Hexafluoroaluminate w-LED Phosphors
Materials 2017, 10(11), 1322; doi:10.3390/ma10111322
Received: 29 September 2017 / Revised: 2 November 2017 / Accepted: 7 November 2017 / Published: 17 November 2017
PDF Full-text (6725 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Mn4+-activated hexafluoroaluminates are promising red-emitting phosphors for white light emitting diodes (w-LEDs). Here, we report the synthesis of Na3AlF6:Mn4+, K3AlF6:Mn4+ and K2NaAlF6:Mn4+ phosphors through a
[...] Read more.
Mn4+-activated hexafluoroaluminates are promising red-emitting phosphors for white light emitting diodes (w-LEDs). Here, we report the synthesis of Na3AlF6:Mn4+, K3AlF6:Mn4+ and K2NaAlF6:Mn4+ phosphors through a simple two-step co-precipitation method. Highly monodisperse large (~20 μm) smoothed-octahedron shaped crystallites are obtained for K2NaAlF6:Mn4+. The large size, regular shape and small size distribution are favorable for application in w-LEDs. All Mn4+-doped hexafluoroaluminates show bright red Mn4+ luminescence under blue light excitation. We compare the optical properties of Na3AlF6:Mn4+, K3AlF6:Mn4+ and K2NaAlF6:Mn4+ at room temperature and 4 K. The luminescence measurements reveal that multiple Mn4+ sites exist in M3AlF6:Mn4+ (M = Na, K), which is explained by the charge compensation that is required for Mn4+ on Al3+ sites. Thermal cycling experiments show that the site distribution changes after annealing. Finally, we investigate thermal quenching and show that the luminescence quenching temperature is high, around 460–490 K, which makes these Mn4+-doped hexafluoroaluminates interesting red phosphors for w-LEDs. The new insights reported on the synthesis and optical properties of Mn4+ in the chemically and thermally stable hexafluoroaluminates can contribute to the optimization of red-emitting Mn4+ phosphors for w-LEDs. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Optical Characterization of Nano- and Microcrystals of EuPO4 Created by One-Step Synthesis of Antimony-Germanate-Silicate Glass Modified by P2O5
Materials 2017, 10(9), 1059; doi:10.3390/ma10091059
Received: 3 July 2017 / Revised: 2 September 2017 / Accepted: 5 September 2017 / Published: 9 September 2017
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Abstract
Technology of active glass-ceramics (GC) is an important part of luminescent materials engineering. The classic method to obtain GC is based on annealing of parent glass in proper temperature and different time periods. Generally, only the bulk materials are investigated as a starting
[...] Read more.
Technology of active glass-ceramics (GC) is an important part of luminescent materials engineering. The classic method to obtain GC is based on annealing of parent glass in proper temperature and different time periods. Generally, only the bulk materials are investigated as a starting host for further applications. However, the effect of an additional heat-treatment process on emission and structural properties during GC processing is omitted. Here, we focus on the possibility of obtaining transparent glass-ceramic doped with europium ions directly with a melt-quenching method. The influence of phosphate concentration (up to 10 mol %) on the inversion symmetry of local environment of Eu3+ ions in antimony-germanate-silicate (SGS) glass has been investigated. The Stark splitting of luminescence spectra and the local asymmetry ratio estimated by relation of (5D07F2)/(5D07F1) transitions in fabricated glass confirms higher local symmetry around Eu3+ ions. Based on XRD and SEM/EDX measurements, the EuPO4 nano- and microcrystals with monoclinic geometry were determined. Therefore, in our experiment, we confirmed possibility of one-step approach to fabricate crystalline structures (glass-ceramic) in Eu–doped SGS glass without additional annealing process. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle The Effect of Heat Treatment on the Emission Color of P-Doped Ca2SiO4 Phosphor
Materials 2017, 10(9), 1000; doi:10.3390/ma10091000
Received: 25 July 2017 / Revised: 21 August 2017 / Accepted: 21 August 2017 / Published: 26 August 2017
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Abstract
In a series of (Ca2–x/2–yEuyx/2)(Si1–xPx)O4 (x = 0.06, 0.02 ≤ y ≤0.5), various color-emitting phosphors were successfully synthesized by a solid-state reaction. These phosphors were characterized
[...] Read more.
In a series of (Ca2–x/2–yEuyx/2)(Si1–xPx)O4 (x = 0.06, 0.02 ≤ y ≤0.5), various color-emitting phosphors were successfully synthesized by a solid-state reaction. These phosphors were characterized by photoluminescence (PL) spectroscopy, X-ray powder diffractometry, transmission electron microscopy, and X-ray absorption fine structure spectroscopy. We evaluated the effect of heat treatment on PL properties with various annealing temperatures at 1373–1773 K for 4 h before/after reduction treatment from Eu3+ to Eu2+. In the red-emitting (Ca1.95Eu3+0.020.03)(Si0.94P0.06)O4+δ phosphor, the highest PL intensity exhibited when it was annealed at 1773 K. On the other hand, in the green-emitting (Ca1.95Eu2+0.020.03)(Si0.94P0.06)O4 phosphor, the highest PL intensity was realized when it was annealed at 1473 K and consequently treated under a reductive atmosphere. With increasing annealing temperature, the emission peak wavelength steadily decreased. Furthermore, with increasing Eu2+ content, the emission peak wavelength increased, with the color of emitting light becoming yellowish. Thus, the PL properties of the phosphors were affected by both the structural change from β to α’L, which occurred by heat treatment, and the amount of doped Eu ions. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Preparation of Luminescent Metal-Organic Framework Films by Soft-Imprinting for 2,4-Dinitrotoluene Sensing
Materials 2017, 10(9), 992; doi:10.3390/ma10090992
Received: 14 July 2017 / Revised: 9 August 2017 / Accepted: 21 August 2017 / Published: 25 August 2017
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Abstract
A novel technique for the creation of metal-organic framework (MOF) films based on soft-imprinting and their use as gas sensors was developed. The microporous MOF material [Zn2(bpdc)2(bpee)] (bpdc = 4,4′-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) was synthesized solvothermally and activated by
[...] Read more.
A novel technique for the creation of metal-organic framework (MOF) films based on soft-imprinting and their use as gas sensors was developed. The microporous MOF material [Zn2(bpdc)2(bpee)] (bpdc = 4,4′-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) was synthesized solvothermally and activated by removing the occluded solvent molecules from its inner channels. MOF particles were characterized by powder X-ray diffraction and fluorescence spectroscopy, showing high crystallinity and intense photoluminescence. Scanning electron microscope images revealed that MOF crystals were mainly in the form of microneedles with a high surface-to-volume ratio, which together with the high porosity of the material enhances its interaction with gas molecules. MOF crystals were soft-imprinted into cellulose acetate (CA) films on quartz at different pressures. Atomic force microscope images of soft-imprinted films showed that MOF crystals were partially embedded into the CA. With this procedure, mechanically stable films were created, with crystals protruding from the CA surface and therefore available for incoming gas molecules. The sensing properties of the films were assessed by exposing them to saturated atmospheres of 2,4-dinitrotoluene, which resulted in a substantial quenching of the fluorescence after few seconds. The soft-imprinted MOF films on CA/quartz exhibit good sensing capabilities for the detection of nitroaromatics, which was attributed to the MOF sensitivity and to the novel and more efficient film processing method based on soft-imprinting. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Insight the Luminescence Properties of AlON: Eu, Mg Phosphor under VUV Excitation
Materials 2017, 10(7), 723; doi:10.3390/ma10070723
Received: 27 April 2017 / Revised: 23 June 2017 / Accepted: 26 June 2017 / Published: 29 June 2017
Cited by 1 | PDF Full-text (2549 KB) | HTML Full-text | XML Full-text
Abstract
Owing to high quantum efficiency, adjustable composition and antioxidation properties of oxynitride phosphors, extensive investigations have focused on their photoluminescence properties under low-energy light excitation (UV or blue light). However, the vacuum ultraviolet (VUV) luminescence properties of oxynitride phosphors are rarely researched. Present
[...] Read more.
Owing to high quantum efficiency, adjustable composition and antioxidation properties of oxynitride phosphors, extensive investigations have focused on their photoluminescence properties under low-energy light excitation (UV or blue light). However, the vacuum ultraviolet (VUV) luminescence properties of oxynitride phosphors are rarely researched. Present work studies the structure and VUV luminescence properties of an oxynitride phosphor: AlON: Eu, Mg, which is synthesized by solid-state reaction. Under 147 nm excitation, it was found that AlON: Eu, Mg phosphor shows a blue emission band centered at about 470 nm. The first principle calculation is used to analyze the origin of the VUV absorption. Compared with BaMgAl10O17: Eu2+ phosphor, AlON: Eu, Mg phosphor shows better thermal stability. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex
Materials 2017, 10(6), 657; doi:10.3390/ma10060657
Received: 19 April 2017 / Revised: 21 May 2017 / Accepted: 8 June 2017 / Published: 16 June 2017
Cited by 1 | PDF Full-text (2154 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A novel orange cationic iridium(III) complex [(TPTA)2Ir(dPPOA)]PF6 (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)2Ir(dPPOA)]PF6 has high thermal stability with a decomposition temperature (Td)
[...] Read more.
A novel orange cationic iridium(III) complex [(TPTA)2Ir(dPPOA)]PF6 (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)2Ir(dPPOA)]PF6 has high thermal stability with a decomposition temperature (Td) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)2Ir(dPPOA)]PF6 was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I’Eclairage) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency (ηL) was 128.5 lm∙W−1. Such a cold white LED became a neutral white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and ηL was 85.2 lm∙W−1. It further became a warm white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and ηL was 46.1 lm∙W−1. The results show that [(TPTA)2Ir(dPPOA)]PF6 is a promising phosphor candidate for fabricating warm white LEDs. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle AC Electroluminescent Processes in Pr3+-Activated (Ba0.4Ca0.6)TiO3 Diphase Polycrystals
Materials 2017, 10(5), 565; doi:10.3390/ma10050565
Received: 24 April 2017 / Revised: 10 May 2017 / Accepted: 16 May 2017 / Published: 21 May 2017
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Abstract
We investigated the properties of alternating current (AC)-driven electroluminescence from (Ba0.4Ca0.6)TiO3:Pr3+ diphase polycrystal-based device. The results of crystal phases and micrographs, and the symmetrical dual emissions in one AC cycle, indicate the spontaneous formation of a
[...] Read more.
We investigated the properties of alternating current (AC)-driven electroluminescence from (Ba0.4Ca0.6)TiO3:Pr3+ diphase polycrystal-based device. The results of crystal phases and micrographs, and the symmetrical dual emissions in one AC cycle, indicate the spontaneous formation of a dielectric/phosphor/dielectric sandwich microstructure in (Ba0.4Ca0.6)TiO3:Pr3+. The electroluminescent device emits a red light of 617 nm, which is attributed to the 1D2-3H4 transition of Pr3+ in the phosphor phase. At a fixed AC frequency, the intensity of electroluminescence exhibits a steep enhancement when applying an increased driving electric field that is beyond a threshold. In a fixed driving electric field, the intensity of electroluminescence shows a rapid rise at low frequencies, but reaches saturation at high frequencies. Based on a double-injection model, we discussed systematically the electroluminescent processes in a whole cycle of AC electric field, which matched well with the experimental data. Our investigation is expected to expand our understanding of such a diphase electroluminescent device, thereby promoting their applications in lighting and displays. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Effect of Partial Crystallization on the Structural and Luminescence Properties of Er3+-Doped Phosphate Glasses
Materials 2017, 10(5), 473; doi:10.3390/ma10050473
Received: 30 March 2017 / Revised: 19 April 2017 / Accepted: 25 April 2017 / Published: 28 April 2017
Cited by 1 | PDF Full-text (25309 KB) | HTML Full-text | XML Full-text
Abstract
Er-doped phosphate glass ceramics were fabricated by melt-quenching technique followed by a heat treatment. The effect of the crystallization on the structural and luminescence properties of phosphate glasses containing Al2O3, TiO2, and ZnO was investigated. The morphological
[...] Read more.
Er-doped phosphate glass ceramics were fabricated by melt-quenching technique followed by a heat treatment. The effect of the crystallization on the structural and luminescence properties of phosphate glasses containing Al2O3, TiO2, and ZnO was investigated. The morphological and structural properties of the glass ceramics were characterized by Field Emission-Scanning Electron Microscopy (FE-SEM), X-ray Diffraction (XRD), and micro-Raman spectroscopy. Additionally, the luminescence spectra and the lifetime values were measured in order to study the influence of the crystallization on the spectroscopic properties of the glasses. The volume ratio between the crystal and the glassy phases increased along with the duration of the heat treatment. The crystallization of the glass ceramics was confirmed by the presence of sharp peaks in the XRD patterns and different crystal phases were identified depending on the glass composition. Sr(PO3)2 crystals were found to precipitate in all the investigated glasses. As evidenced by the spectroscopic properties, the site of the Er3+ ions was not strongly affected by the heat treatment except for the fully crystallized glass ceramic which does not contain Al2O3, TiO2, and ZnO. An increase of the lifetime was also observed after the heat treatment of this glass. Therefore, we suspect that the Er3+ ions are incorporated in the precipitated crystals only in this glass ceramic. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Open AccessArticle Tunable Luminescence in Sr2MgSi2O7:Tb3+, Eu3+Phosphors Based on Energy Transfer
Materials 2017, 10(3), 227; doi:10.3390/ma10030227
Received: 22 December 2016 / Accepted: 17 February 2017 / Published: 24 February 2017
Cited by 1 | PDF Full-text (4166 KB) | HTML Full-text | XML Full-text
Abstract
A series of Tb3+, Eu3+-doped Sr2MgSi2O7 (SMSO) phosphors were synthesized by high temperature solid-state reaction. X-ray diffraction (XRD) patterns, Rietveld refinement, photoluminescence spectra (PL), and luminescence decay curves were utilized to characterize each sample’s properties. Intense green emission due to Tb3+ 5D4→7F5 transition
[...] Read more.
A series of Tb3+, Eu3+-doped Sr2MgSi2O7 (SMSO) phosphors were synthesized by high temperature solid-state reaction. X-ray diffraction (XRD) patterns, Rietveld refinement, photoluminescence spectra (PL), and luminescence decay curves were utilized to characterize each sample’s properties. Intense green emission due to Tb3+ 5D4→7F5 transition was observed in the Tb3+ single-doped SMSO sample, and the corresponding concentration quenching mechanism was demonstrated to be a diople-diople interaction. A wide overlap between Tb3+ emission and Eu3+ excitationspectraresults in energy transfer from Tb3+ to Eu3+. This has been demonstrated by the emission spectra and decay curves of Tb3+ in SMSO:Tb3+, Eu3+ phosphors. Energy transfer mechanism was determined to be a quadrupole-quadrupole interaction. And critical distance of energy transfer from Tb3+ to Eu3+ ions is calculated to be 6.7 Å on the basis of concentration quenching method. Moreover, white light emission was generated via adjusting concentration ratio of Tb3+ and Eu3+ in SMSO:Tb3+, Eu3+ phosphors. All the results indicate that SMSO:Tb3+, Eu3+ is a promising single-component white light emitting phosphor. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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Review

Jump to: Research

Open AccessFeature PaperReview Luminescent Lanthanoid Calixarene Complexes and Materials
Materials 2017, 10(12), 1369; doi:10.3390/ma10121369
Received: 29 October 2017 / Revised: 20 November 2017 / Accepted: 20 November 2017 / Published: 28 November 2017
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Abstract
This review aims to provide an overview of recent examples of lanthanoid-calixarene complexes incorporated into light-emitting materials. Background information on the antenna effect and early work on lanthanoid complexes on calixarenes is provided to set the context. Classes of materials discussed include polymers,
[...] Read more.
This review aims to provide an overview of recent examples of lanthanoid-calixarene complexes incorporated into light-emitting materials. Background information on the antenna effect and early work on lanthanoid complexes on calixarenes is provided to set the context. Classes of materials discussed include polymers, nanoparticles, and metal clusters. Full article
(This article belongs to the Special Issue Luminescent Materials 2017)
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