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13 pages, 3048 KiB

Open AccessArticle

Thermal Quenching of Intrinsic Photoluminescence in Amorphous and Monoclinic HfO₂ Nanotubes

by Artem Shilov, Sergey Savchenko, Alexander Vokhmintsev, Kanat Zhusupov and Ilya Weinstein

Materials 2024, 17(22), 5587; https://doi.org/10.3390/ma17225587 - 15 Nov 2024

Viewed by 299

Abstract

Nanotubular hafnia arrays hold significant promise for advanced opto- and nanoelectronic applications. However, the known studies concern mostly the luminescent properties of doped HfO₂-based nanostructures, while the optical properties of nominally pure hafnia with optically active centers of intrinsic origin are [...] Read more.

Nanotubular hafnia arrays hold significant promise for advanced opto- and nanoelectronic applications. However, the known studies concern mostly the luminescent properties of doped HfO₂-based nanostructures, while the optical properties of nominally pure hafnia with optically active centers of intrinsic origin are far from being sufficiently investigated. In this work, for the first time we have conducted research on the wide-range temperature effects in the photoluminescence processes of anion-defective hafnia nanotubes with an amorphous and monoclinic structure, synthesized by the electrochemical oxidation method. It is shown that the spectral parameters, such as the position of the maximum and half-width of the band, remain almost unchanged in the range of 7–296 K. The experimental data obtained for the photoluminescence temperature quenching are quantitatively analyzed under the assumption made for two independent channels of non-radiative relaxation of excitations with calculating the appropriate energies of activation barriers—9 and 39 meV for amorphous hafnia nanotubes, 15 and 141 meV for monoclinic ones. The similar temperature behavior of photoluminescence spectra indicates close values of short-range order parameters in the local atomic surrounding of the active emission centers in hafnium dioxide with amorphous and monoclinic structure. Anion vacancies

V_{O}^{-}

and

V_{O}^{2 -}

appeared in the positions of three-coordinated oxygen and could be the main contributors to the spectral features of emission response and observed thermally stimulated processes. The recognized and clarified mechanisms occurring during thermal quenching of photoluminescence could be useful for the development of light-emitting devices and thermo-optical sensors with functional media based on oxygen-deficient hafnia nanotubes. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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21 pages, 2539 KiB

Open AccessArticle

Photoluminescence Spectra of Helium Ion-Implanted Diamond

by Andrey A. Khomich, Alexey Popovich and Alexander V. Khomich

Materials 2024, 17(21), 5168; https://doi.org/10.3390/ma17215168 - 23 Oct 2024

Viewed by 485

Abstract

Ion implantation in diamond crystals is widely used both for producing conducting microstructures in the bulk of the material and for creating isolated photon emitters in quantum optics, photonics, cryptography, and biosensorics. The photoluminescence (PL) spectra of helium ion-implanted diamonds are dominated by [...] Read more.

Ion implantation in diamond crystals is widely used both for producing conducting microstructures in the bulk of the material and for creating isolated photon emitters in quantum optics, photonics, cryptography, and biosensorics. The photoluminescence (PL) spectra of helium ion-implanted diamonds are dominated by two sharp emission lines, HR1 and HR2 (from Helium-Related), at ~536 and 560 nm. Here, we report on PL studies of helium-related optical centers in diamonds. Experiments have been carried out on a (110) plate of natural single-crystal type IIa diamonds. The uniform distribution of radiation defects in a 700 nm-thick layer was obtained by ten cycles of multiple-energy (from 24 to 350 kV) helium ion implantation with a total dose of 5 × 10¹⁶ cm⁻². The diamonds were annealed in steps in a vacuum oven at temperatures from 200 to 1040 °C. It is demonstrated that helium ion implantation in diamonds followed by annealing gives rise to more than a dozen various centers that are observed in the PL spectra in the range of 530–630 nm. The transformations of the PL spectra due to annealing are investigated in detail. The spectral shapes of phonon sidebands are determined for the HR1, HR2, and HR3 bands with ZPLs at ~536, 560, and 577 nm, respectively, and it is shown that these bands are attributed to interstitial-related centers in diamonds. The reported results are important for understanding the structure and properties of helium-related defects in diamonds. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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12 pages, 1588 KiB

Open AccessArticle

Application of Fluorescent Carbon Dots as Catalysts for the Ring-Opening Reaction of Epoxides

by Diana M. A. Crista, Joaquim C. G. Esteves da Silva and Luís Pinto da Silva

Materials 2023, 16(24), 7620; https://doi.org/10.3390/ma16247620 - 13 Dec 2023

Viewed by 1120

Abstract

Considering the increased anthropogenic emissions of CO₂ into the atmosphere, it is important to develop economic incentives for the use of CO₂ capture methodologies. The conversion of CO₂ into heterocyclic carbonates shows significant potential. However, there is a need for [...] Read more.

Considering the increased anthropogenic emissions of CO₂ into the atmosphere, it is important to develop economic incentives for the use of CO₂ capture methodologies. The conversion of CO₂ into heterocyclic carbonates shows significant potential. However, there is a need for suitable organocatalysts to reach the required efficiency for these reactions. Given this, there has been an increasing focus on the development of organocatalytic systems consisting of a nucleophile and a hydrogen bond donor (HBD) so that CO₂ conversion can occur in ambient conditions. In this work, we evaluated the potential of fluorescent carbon dots (CDs) as catalytic HBDs in the ring-opening reaction of epoxides, which is typically the rate-limiting step of CO₂ conversion reactions into heterocyclic carbonates. The obtained results demonstrated that the CDs had a relevant catalytic effect on the studied model reaction, with a rate constant of 0.2361 ± 0.008 h⁻¹, a percentage of reactant conversion of 70.8%, and a rate constant enhancement of 32.2%. These results were better than the studied alternative molecular HBDs. Thus, this study demonstrated that CDs have the potential to be used as HBDs and employed in organocatalyzed CO₂ conversion into value-added products. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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17 pages, 16459 KiB

Open AccessArticle

Vertically Well-Aligned ZnO Nanoscintillator Arrays with Improved Photoluminescence and Scintillation Properties

by Murat Kurudirek, Sinem V. Kurudirek, Nolan E. Hertel, Anna Erickson, Paul J. Sellin, Sharmistha Mukhopadhyay, Aykut Astam and Christopher J. Summers

Materials 2023, 16(20), 6717; https://doi.org/10.3390/ma16206717 - 17 Oct 2023

Cited by 2 | Viewed by 1067

Abstract

ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical [...] Read more.

ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical and scintillation properties of the ZnO nanostructures. Measurement of the nanorod (NR) length, corresponding photoluminescence (PL) and scintillation spectra and their dependence on the additives present in the solution are discussed. ZnO NRs grown on a silica substrate, whose UV transmission was found to be better than glass, showed high-quality structural and optical properties. It was found that the addition of sodium citrate significantly reduced defects and correspondingly increased the intrinsic near-band-edge (NBE) UV emission intensity at ~380 nm. To obtain high-quality nanostructures, samples were annealed in a 10% H₂ + 90% N₂ atmosphere. The anneal in the forming gas atmosphere enhanced the emission of the UV peak by reducing defects in the nanostructure. NRs are highly tapered towards the end of the structure. The tapering process was monitored using time growth studies, and its effect on PL and reflectance spectra are discussed. A good alpha particle response was obtained for the grown ZnO NRs, confirming its potential to be used as an alpha particle scintillator. After optimizing the reaction parameters, it was concluded that when ammonium hydroxide and sodium citrate were used, vertically well-aligned and long ZnO nanoarrays with highly improved optical and scintillation properties were obtained. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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8 pages, 902 KiB

Open AccessCommunication

Acceleration of Near-IR Emission through Efficient Surface Passivation in Cd₃P₂ Quantum Dots

by Logan Smith, K. Elena Harbison, Benjamin T. Diroll and Igor Fedin

Materials 2023, 16(19), 6346; https://doi.org/10.3390/ma16196346 - 22 Sep 2023

Viewed by 1500

Abstract

Fast near-IR (NIR) emitters are highly valuable in telecommunications and biological imaging. The most established NIR emitters are epitaxially grown In_xGa_1−xAs quantum dots (QDs), but epitaxial growth has several disadvantages. Colloidal synthesis is a viable alternative that produces a [...] Read more.

Fast near-IR (NIR) emitters are highly valuable in telecommunications and biological imaging. The most established NIR emitters are epitaxially grown In_xGa_1−xAs quantum dots (QDs), but epitaxial growth has several disadvantages. Colloidal synthesis is a viable alternative that produces a few NIR-emitting materials, but they suffer from long photoluminescence (PL) times. These long PL times are intrinsic in some NIR materials (PbS, PbSe) but are attributed to emission from bright trapped carrier states in others. We show that Cd₃P₂ QDs possess substantial trap emission with radiative times >10¹ ns. Surface passivation through shell growth or coordination of Lewis acids is shown to accelerate the NIR emission from Cd₃P₂ QDs by decreasing the amount of trap emission. This finding brings us one step closer to the application of colloidally synthesized QDs as quantum emitters. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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10 pages, 3085 KiB

Open AccessArticle

Scintillation Properties of Ba₃RE(PO₄)₃ Single Crystals (RE = Y, La, Lu)

by Yuma Takebuchi, Masanori Koshimizu, Kensei Ichiba, Takumi Kato, Daisuke Nakauchi, Noriaki Kawaguchi and Takayuki Yanagida

Materials 2023, 16(13), 4502; https://doi.org/10.3390/ma16134502 - 21 Jun 2023

Cited by 8 | Viewed by 1334

Abstract

Eulytite-type Ba₃RE(PO₄)₃ (RE = Y, La, and Lu) single crystals were synthesized by the floating zone method, and their scintillation properties were investigated. The powder X-ray diffraction measurement revealed that the single phase of Ba₃RE(PO₄ [...] Read more.

Eulytite-type Ba₃RE(PO₄)₃ (RE = Y, La, and Lu) single crystals were synthesized by the floating zone method, and their scintillation properties were investigated. The powder X-ray diffraction measurement revealed that the single phase of Ba₃RE(PO₄)₃ samples were successfully synthesized. The samples exhibited a luminescence peak due to self-trapped exciton at around 400 nm under vacuum ultraviolet and X-ray irradiation. The X-ray-induced scintillation decay time constants of the samples were several microseconds at room temperature. In the ²⁴¹Am α-ray irradiated pulse height spectra, all the samples showed a clear full energy peak, and the absolute light yields of the Ba₃Y(PO₄)₃, Ba₃La(PO₄)₃, and Ba₃Lu(PO₄)₃ single crystals were estimated to be 960, 1160, and 1220 ph/5.5 MeV-α, with a typical error of ±10%, respectively. The scintillation light yields of the Ba₃RE(PO₄)₃ have been quantitatively clarified for the first time. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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12 pages, 3842 KiB

Open AccessEditor’s ChoiceArticle

Upconversion Emission Studies in Er^3+/Yb³⁺ Doped/Co-Doped NaGdF₄ Phosphor Particles for Intense Cathodoluminescence and Wide Temperature-Sensing Applications

by Abhishek Kumar, Helena Couto and Joaquim C. G. Esteves da Silva

Materials 2022, 15(19), 6563; https://doi.org/10.3390/ma15196563 - 21 Sep 2022

Cited by 4 | Viewed by 1880

Abstract

Er³⁺/Yb³⁺ doped/co-doped NaGdF₄ upconversion phosphor nanoparticles were synthesized via the thermal decomposition route of synthesis. The α-phase crystal structure and nanostructure of these particles were confirmed using XRD and FE-SEM analysis. In the power-dependent upconversion analysis, different emission bands [...] Read more.

Er³⁺/Yb³⁺ doped/co-doped NaGdF₄ upconversion phosphor nanoparticles were synthesized via the thermal decomposition route of synthesis. The α-phase crystal structure and nanostructure of these particles were confirmed using XRD and FE-SEM analysis. In the power-dependent upconversion analysis, different emission bands at 520 nm, 540 nm, and 655 nm were obtained. The sample was also examined for cathodoluminescence (CL) analysis at different filament currents of an electron beam. Through CL analysis, different emission bands of 526 nm, 550 nm, 664 nm, and 848 nm were obtained. The suitability of the present sample for temperature-sensing applications at a wide range of temperatures, from room temperature to 1173 K, was successfully demonstrated. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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22 pages, 4000 KiB

Open AccessArticle

Life Cycle Assessment-Based Comparative Study between High-Yield and “Standard” Bottom-Up Procedures for the Fabrication of Carbon Dots

by Sónia Fernandes, Joaquim C. G. Esteves da Silva and Luís Pinto da Silva

Materials 2022, 15(10), 3446; https://doi.org/10.3390/ma15103446 - 11 May 2022

Cited by 6 | Viewed by 2045

Abstract

Carbon dots (CDs) are carbon-based nanomaterials with remarkable properties that can be produced from a wide variety of synthesis routes. Given that “standard” bottom-up procedures are typically associated with low synthesis yields, different authors have been trying to devise alternative high-yield fabrication strategies. [...] Read more.

Carbon dots (CDs) are carbon-based nanomaterials with remarkable properties that can be produced from a wide variety of synthesis routes. Given that “standard” bottom-up procedures are typically associated with low synthesis yields, different authors have been trying to devise alternative high-yield fabrication strategies. However, there is a doubt if sustainability-wise, the latter should be really preferred to the former. Herein, we employed a Life Cycle Assessment (LCA) approach to compare and understand the environmental impacts of high-yield and “standard” bottom-up strategies, by applying different life cycle impact assessment (LCIA) methods. These routes were: (1) production of hydrochar, via the hydrothermal treatment of carbon precursors, and its alkaline peroxide treatment into high-yield CDs; (2) microwave treatment of carbon precursors doped with ethylenediamine; (3) and (6) thermal treatment of carbon precursor and urea; (4) hydrothermal treatment of carbon precursor and urea; (5) microwave treatment of carbon precursor and urea. For this LCA, four LCIA methods were used: ReCiPe, Greenhouse Gas Protocol, AWARE, and USEtox. Results identified CD-5 as the most sustainable synthesis in ReCiPe, Greenhouse Gas Protocol, and USEtox. On the other hand, in AWARE, the most sustainable synthesis was CD-1. It was possible to conclude that, in general, high-yield synthesis (CD-1) was not more sustainable than “standard” bottom-up synthesis, such as CD-5 and CD-6 (also with relatively high-yield). More importantly, high-yield synthesis (CD-1) did not generate much lower environmental impacts than “standard” approaches with low yields, which indicates that higher yields come with relevant environmental costs. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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Review

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23 pages, 3434 KiB

Open AccessReview

Negative Thermal Quenching of Photoluminescence: An Evaluation from the Macroscopic Viewpoint

by Shirun Yan

Materials 2024, 17(3), 586; https://doi.org/10.3390/ma17030586 - 25 Jan 2024

Cited by 2 | Viewed by 1449

Abstract

Negative thermal quenching (NTQ) denotes that the integral emission spectral intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. NTQ has been the subject of intensive investigations in recent years, and a large number of phosphors [...] Read more.

Negative thermal quenching (NTQ) denotes that the integral emission spectral intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. NTQ has been the subject of intensive investigations in recent years, and a large number of phosphors are reported to have exhibited NTQ. In this paper, a collection of results in the archival literature about NTQ of specific phosphors is discussed from a macroscopic viewpoint, focusing on the following three aspects: (1) Could the NTQ of a given phosphor be reproducible? (2) Could the associated data for a given phosphor exhibiting NTQ be in line with the law of the conservation of energy? (3) Could the NTQ of a given phosphor be demonstrated in a prototype WLED device? By analyzing typical cases based on common sense, we hope to increase awareness of the issues with papers reporting the NTQ of specific phosphors based on spectral intensity, along with the importance of maintaining stable and consistent measurement conditions in temperature-dependent spectral intensity measurement, which is a prerequisite for the validity of the measurement results. Full article

(This article belongs to the Special Issue Advances in Luminescent Materials)

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