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| 4. |
- Hastings-Simon, S R, et al.
(författare)
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Spectral hole-burning spectroscopy in Nd3+: YVO4
- 2008
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 77:12
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Tidskriftsartikel (refereegranskat)abstract
- We present spectral hole-burning measurements on the 879 nm, I-4(9/2) -> F-4(3/2) transition in Nd3+ : YVO4. We observe antiholes in the spectrum along with long lived spectral holes, which demonstrates optical pumping between the ground state Zeeman levels. The spectral holes are narrow (homogeneous linewidth of 63 kHz) at 2.1 K with a 300 mT applied magnetic field. We also perform preliminary spectral tailoring in this material by creating a 40 MHz wide transmission window in the inhomogeneous absorption. These results show the potential of the Zeeman levels in Nd doped materials to be used for spectral tailoring for quantum and classical information processing.
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| 8. |
- Moncorge, R, et al.
(författare)
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Linear and non-linear spectroscopy of Ho3+-doped YVO4 and LuVO4
- 2005
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 17:42, s. 6751-6762
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Tidskriftsartikel (refereegranskat)abstract
- Rare-earth-doped crystals can be attractive materials for quantum information processing, because of the long coherence times that can be expected, in particular, from non-Kramers ions. In this paper, Ho3+-doped yttrium and lutetium vanadate single crystals have been investigated using linear and coherent optical spectroscopy. For Ho3+:YVO4, the crystal-field levels of the I-5(8), F-5, F-5(4) and S-5(2) multiplets have been determined and compared with crystal-field level calculations. This allowed us to unambiguously assign most of the observed transitions, although some results suggest that the site symmetry of the Ho3+ ion could deviate from D-2d. Similar conclusions were reached for Ho3+:LuVO4. Hole burning measurements indicate that the coherence time of the I-5(8)-F-5(5) optical transitions is rather short in both compounds (around 40 ns). Assuming that the coherence is limited by spin interactions, this is accounted for by the high nuclear moment of the nearby vanadium ions, since the large crystal-field level splittings of the I-5(8) and F-5(5) multiplets do not favour a large enhanced nuclear Zeeman effect.
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| 10. |
- Fluri, A., et al.
(författare)
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Anisotropic Proton and Oxygen Ion Conductivity in Epitaxial Ba2In2O5 Thin Films
- 2017
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:40, s. 21797-21805
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Tidskriftsartikel (refereegranskat)abstract
- Solid oxide oxygen ion and proton conductors are a highly important class of materials for renewable energy conversion devices like solid oxide fuel cells. Ba2In2O5 (BIO) exhibits both oxygen ion and proton conduction, in a dry and humid environment, respectively. In a dry environment, the brownmillerite crystal structure of BIO exhibits an ordered oxygen ion sublattice, which has been speculated to result in anisotropic oxygen ion conduction. The hydrated structure of BIO, however, resembles a perovskite and the protons in it were predicted to be ordered in layers. To complement the significant theoretical and experimental efforts recently reported on the potentially anisotropic conductive properties in BIO, we measure here both the proton and oxygen ion conductivity along different crystallographic directions. Using epitaxial thin films with different crystallographic orientations, the charge transport for both charge carriers is shown to be anisotropic. The anisotropy of the oxygen ion conduction can indeed be explained by the layered structure of the oxygen sublattice of BIO. The anisotropic proton conduction, however, further supports the suggested ordering of the protonic defects in the material. The differences in proton conduction along different crystallographic directions attributed to proton ordering in BIO are of a similar extent as those observed along different crystallographic directions in materials where proton ordering is not present but where protons find preferential conduction pathways through chainlike or layered structures.
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| 11. |
- Haro-Gonzalez, P., et al.
(författare)
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Eu3+ as a luminescent probe for the local structure of trivalent dopant ions in barium zirconate-based proton conductors
- 2013
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 247, s. 94-97
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Tidskriftsartikel (refereegranskat)abstract
- The luminescence spectra and decay kinetics of dry and hydrated samples of BaZr0.9Y0.099Eu0.001O2.95 have been measured at room temperature. The spectra of the dry sample evidence two D-5(0) -> F-7(0) bands clearly indicating that Eu3+ (replacing Y3+ in the Zr4+ position of the average cubic perovskite structure) occupies two different local structures, whilst only one Eu3+ site is observed for the hydrated material. From the spectral data, it is possible to identify the nature of these two sites and to propose point group symmetries for the average local geometry around Eu3+. The decay time of the D-5(0) level becomes shorter upon hydration, due to the interaction with high-frequency O-H stretching vibrations, indicating an attractive interaction between protons and dopant atoms. (C) 2013 Elsevier B.V. All rights reserved.
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| 12. |
- Lin, Yuan-Chih, 1987, et al.
(författare)
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Inorganic Phosphor Materials for Lighting
- 2016
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Ingår i: Topics in Current Chemistry. - : Springer Science and Business Media LLC. - 0340-1022 .- 2365-0869 .- 2364-8961. ; 374:2, s. 374-421
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Forskningsöversikt (refereegranskat)abstract
- This chapter addresses the development of inorganic phosphor materials capable of converting the near UV or blue radiation emitted by a light emitting diode to visible radiation that can be suitably combined to yield white light. These materials are at the core of the new generation of solid-state lighting devices that are emerging as a crucial clean and energy saving technology. The chapter introduces the problem of white light generation using inorganic phosphors and the structure-property relationships in the broad class of phosphor materials, normally containing lanthanide or transition metal ions as dopants. Radiative and non-radiative relaxation mechanisms are briefly described. Phosphors emitting light of different colors (yellow, blue, green, and red) are described and reviewed, classifying them in different chemical families of the host (silicates, phosphates, aluminates, borates, and non-oxide hosts). This research field has grown rapidly and is still growing, but the discovery of new phosphor materials with optimized properties (in terms of emission efficiency, chemical and thermal stability, color, purity, and cost of fabrication) would still be of the utmost importance.
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| 13. |
- Lin, Yuan-Chih, 1987, et al.
(författare)
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Understanding the Interactions between Vibrational Modes and Excited State Relaxation in Y₃₋ₓCeₓAl₅O₁₂: Design Principles for Phosphors Based on 5d-4f Transitions
- 2018
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 30:6, s. 1865-1877
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Tidskriftsartikel (refereegranskat)abstract
- The oxide garnet Y 3 Al 5 O 12 (YAG), when a few percent of the activator ions Ce 3+ substitutes for Y 3+ , is a luminescent material widely used in phosphor-converted white lighting. However, fundamental questions surrounding the defect chemistry and luminescent per formance of this material remain, especially in regard to the nature and role of vibrational dynamics. Here, we provide a complete phonon assignment of YAG and establish the general spectral trends upon variation of the Ce 3+ dopant concentration and temperature, which are shown to correlate with the macroscopic luminescence properties of Y 3-x Ce x Al 5 O 12 . Increasing the Ce 3+ concentration and/or temperature leads to a red-shift of the emitted light, as a result of increased crystal-field splitting due to a larger tetragonal distortion of the CeO 8 moieties. Decreasing the Ce 3+ concentration or cosubstitution of smaller and/or lighter atoms on the Y sites creates the potential to suppress thermal quenching of luminescence because the frequencies of phonon modes important for nonradiative relaxation mechanisms are upward-shifted and hence less readily activated. It follows that design principles for finding new Ce 3+ -doped oxide phosphors emitting at longer wavelengths require tetragonally distorted environments around the CeO 8 moieties and a sufficiently rigid host structure and/or low activator-ion concentration to avoid thermal quenching of luminescence.
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| 14. |
- Lin, Yuan-Chih, 1987, et al.
(författare)
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Unraveling the impact of different thermal quenching routes on the luminescence efficiency of the Y3Al5O12:Ce3+ phosphor for white light emitting diodes
- 2020
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7534 .- 2050-7526. ; 8:40, s. 14015-14027
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Tidskriftsartikel (refereegranskat)abstract
- Cerium doped yttrium aluminium garnet, Y3-zCezAl5O12, is the prototype material for solid-state white lighting and it still is an important white LED phosphor. However, fundamental understanding of the thermal quenching of luminescence, which leads to a pronounced reduction of the emission intensity under high-power light-emitting diode operation, remains to be obtained. Here we show, through a multitechnique approach based on photoluminescence, thermoluminescence and mode-selective vibrational excitation experiments that thermal quenching of luminescence in Y3-zCezAl5O12 is caused by a combined effect of thermal ionization, thermally activated concentration quenching, and thermally activated 5d → 4f crossover relaxation via electron-phonon coupling, and establish the general trends upon variation of the Ce3+ concentration and temperature. Thermal quenching below 600 K is primarily the result of concentration quenching and crossover relaxation, which can be suppressed by keeping the Ce3+ dopant concentration far below 0.7 mol%, whereas for temperatures above 600 K thermal ionization is the predominating quenching process. This new insight into the interplay between different thermal quenching processes provides design principles for optimizing the light emittance and colour stability of new phosphor materials used in white lighting devices characterized by certain operating temperatures. This journal is
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| 15. |
- Lin, Yuan-Chih, 1987, et al.
(författare)
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Unraveling the Mechanisms of Thermal Quenching of Luminescence in Ce3+-Doped Garnet Phosphors †
- 2019
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 31:11, s. 3851-3862
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Forskningsöversikt (refereegranskat)abstract
- The environmental and economic benefits of phosphor-converted white-light-emitting diodes (pc-WLEDs) have been increasingly appreciated in recent years. However, a significant challenge in this field pertains to a phenomenon known as thermal quenching, which takes place inside phosphors and leads to a pronounced reduction of the emission intensity under high-power light-emitting diode operation. The development of new, more thermally stable phosphors depends on a better understanding of the mechanisms underpinning thermal quenching in phosphors. Here we review the current understanding of thermal quenching mechanisms in Ce3+-doped garnet phosphors, which are widely considered one of the most important families of phosphors for application in pc-WLEDs. In particular, we highlight key structural and dynamical properties, such as the coordination environment of the Ce3+ ions, phonons and local vibrational modes, and structural and chemical defects, which are shown to correlate with phosphor performance. We also discuss the perspectives for future studies in this field in hopes of accelerating the development of new efficient phosphors featuring suppressed thermal quenching of luminescence.
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| 16. |
- Sharma, Suchinder, 1982, et al.
(författare)
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Green persistent luminescence excitable by multiple wavelengths in the CaSc2O4:Ce3+ phosphor co-doped with Mg2
- 2018
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 196, s. 437-441
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Tidskriftsartikel (refereegranskat)abstract
- Calcium scandate (CaSc 2 O 4 ), when substituted with a small amount of the activator ion Ce 3+ to replace Ca 2+ , is a recently discovered green-emitting phosphor promising for solid-state lighting applications. The co-doping with aliovalent ions to compensate for the net positive charge, as induced by the Ce 3+ dopants, is a common approach to change the defect structure and tune the performance of the phosphor, but the underlying mechanisms are unclear. Here we investigate the effect of co-doping with charge-compensating Mg 2+ to substitute for Sc 3+ , using photoluminescence and thermoluminescence techniques. In comparison to the defect structure in Ce 3+ doped CaSc 2 O 4 , the co-doping with charge-compensating Mg 2+ leads to the formation of new traps. These traps are featured by activation energies in the range 0.58–0.64 eV, can be emptied at room temperature and show green long-lasting phosphorescence after excitation at 454, 340, and 254 nm, respectively. Analysis of the spectroscopic results in terms of a vacuum referred binding energy diagram allows us to reach at a plausible luminescence mechanism in {Ce 3+ /Ce 3+ Mg 2+ }-doped CaSc 2 O 4 .
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| 17. |
- Sharma, Suchinder, 1982, et al.
(författare)
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Influence of Ce3+ Concentration on the Thermal Stability and Charge-Trapping Dynamics in the Green Emitting Phosphor CaSc2O4:Ce3
- 2017
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:41, s. 23096-23103
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the Ce3+ concentration on the excitation and emission characteristics, thermal stability, and charge-trapping-detrapping dynamics, of the green-emitting phosphor Ce3+ doped calcium scandium oxide (CaSc2O4) with very dilute Ce3+ substitutions (0.5, 1.0, and 1.5%), has been investigated using optical spectroscopy techniques. The diffuse reflectance and excitation spectra are found to exhibit a nonsystematic behavior with varying Ce3+ concentration, mainly linked to spectral band-overlap, whereas the emission spectra display only minor changes with varying Ce3+ concentration, suggesting that the local structural coordination of the Ce3+ dopants remains the same for different Ce3+ dopant levels. The major impact of Ce3+ concentration is seen on the thermal quenching temperature, which is found to be as high as T-50% approximate to 600 K for the most dilute Ce3+ doping (0.5%), followed by T-50% approximate to 530 K for 1.0% doping and T-50% approximate to 500 K for 1.5% doping, respectively. The materials are found to display a red-shift of the emitted light from 518 to 535 nm with increasing temperature from T = 80 K to T = 800 K, for all Ce3+ dopant levels. Thermoluminescence glow curves provide evidence for five charge-trapping defects, which are found to exhibit different charge-trapping dynamics for excitation into different 5d levels. It is argued that the three deeper traps can be filled by athermal tunneling of charges from the Ce3+ 5d(1) level, while the two shallower traps can only be filled when the charges move through the conduction band of the material.
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| 18. |
- Sharma, Suchinder, 1982, et al.
(författare)
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Weak thermal quenching of the luminescence in the Ca3Sc2Si3O12:Ce3+ garnet phosphor
- 2018
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7534 .- 2050-7526. ; 6:33, s. 8923-8933
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Tidskriftsartikel (refereegranskat)abstract
- We report results of the luminescence properties of the three garnet type phosphors Ce3+-doped Ca3Sc2Si3O12(CSSO:Ce3+), Sr3Y2Ge3O12(SYG:Ce3+) and Y3Al5O12(YAG:Ce3+), investigated using optical spectroscopy techniques and vacuum referred binding energy (VRBE) diagram analysis. By monitoring the temperature dependence of the luminescence decay time we establish an excellent, intrinsic, thermal stability of luminescence in CSSO:Ce3+, with a nearly constant decay time (≈60 ns) up to, at least, T = 860 K. In comparison, SYG:Ce3+and YAG:Ce3+exhibit a significant reduction of the luminescence decay time upon heating, starting at around T = 280 K and T = 550 K, respectively, suggesting a lower internal thermal stability of luminescence in these two garnet phosphors. These findings are supported by the energy separation between the Ce3+5d1level and the conduction band (CB) of the respective hosts, which are found at 1.36 eV (CSSO:Ce3+), 0.45 eV (SYG:Ce3+), and 1.17 eV (YAG:Ce3+), respectively, as predicted by their VRBE diagrams. The performance of CSSO:Ce3+was evaluated by applying the phosphor on a blue InGaN LED. The system shows a luminous efficacy of optical radiation of 243 lm W-1and a linear response with increasing applied voltage, suggesting it is a highly promising phosphor for future technological applications, particularly at high temperature operating environments.
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