Electronic structure and optical properties of the lanthanide activated RE3(Al1−xGax)5O12 (RE=Gd, Y, Lu) garnet compounds
TL;DR: In this article, the properties of the lanthanide dopants in the RE3(Al1−xGax)5O12 (RE=Gd, Y, Lu and x=0, 0.2.
About: This article is published in Journal of Luminescence.The article was published on 2013-02-01. It has received 270 citations till now. The article focuses on the topics: Lanthanide & Electronic structure.
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TL;DR: In this paper, a review of the recent advances in the discovery and structural design of LED phosphors is presented, including the discovery of the novel phosphors from the existing structural models, discovery of new crystal materials by doping and structural modification of the known phosphors.
848 citations
TL;DR: This review will provide insight into the relation between crystal chemistry and luminescence for the important class of Ce3+-doped garnet phosphors, and summarize previous research on the structural design and optical properties of garnet phosphate materials to discuss future research opportunities.
Abstract: Garnets have the general formula of A3B2C3O12 and form a wide range of inorganic compounds, occurring both naturally (gemstones) and synthetically. Their physical and chemical properties are closely related to the structure and composition. In particular, Ce3+-doped garnet phosphors have a long history and are widely applied, ranging from flying spot cameras, lasers and phosphors in fluorescent tubes to more recent applications in white light LEDs, as afterglow materials and scintillators for medical imaging. Garnet phosphors are unique in their tunability of the luminescence properties through variations in the {A}, [B] and (C) cation sublattice. The flexibility in phosphor composition and the tunable luminescence properties rely on design and synthesis strategies for new garnet compositions with tailor-made luminescence properties. It is the aim of this review to discuss the variation in luminescence properties of Ce3+-doped garnet materials in relation to the applications. This review will provide insight into the relation between crystal chemistry and luminescence for the important class of Ce3+-doped garnet phosphors. It will summarize previous research on the structural design and optical properties of garnet phosphors and also discuss future research opportunities in this field.
762 citations
TL;DR: The major achievements and research and development trends from the last decade in the field of single crystal scintillator materials are described in this paper, where two material families are included, namely, those of halide and oxide compounds.
Abstract: In this review, the major achievements and research and development (R&D) trends from the last decade in the field of single crystal scintillator materials are described. Two material families are included, namely, those of halide and oxide compounds. In most cases, the host crystals are doped with Ce3+, Pr3+ or Eu2+ rare earth ions. Their spin- and parity-allowed 5d–4f transitions enable a rapid scintillation response, on the order of tens to hundreds of nanoseconds. Technological recipes, extended characterization by means of optical and magnetic spectroscopies, and theoretical studies are described. The latter provide further support to experimental results and provide a better understanding of the host electronic band structure, energy levels of specific defects, and the emission centers themselves. Applications in medical imaging and dosimetry, security measures, high-energy physics and the high-tech industry, in which X(γ)-rays or particle beams are used and monitored, are recognized as the main driving factor for R&D activities in this field.
493 citations
TL;DR: In this article, a review of persistent luminescence (PersL) can be found, starting from the introduction of longstanding histories of PersL, providing comprehensive insights into its physical mechanism.
378 citations
TL;DR: In this paper, the authors investigated the possibility of thermal ionization as a cause of the quenching process by measuring thermoluminescence (TL) excitation spectra at various temperatures.
Abstract: Y3Al5O12(YAG):Ce3+ is the most widely applied phosphor in white LEDs (w-LEDs) because of strong blue absorption and efficient yellow luminescence combined with a high stability and thermal quenching temperature, required for the extreme operating conditions in high-power w-LEDs. The high luminescence quenching temperature (∼600 K) has been well established, but surprisingly, the mechanism for temperature quenching has not been elucidated yet. In this report we investigate the possibility of thermal ionization as a cause of this quenching process by measuring thermoluminescence (TL) excitation spectra at various temperatures. In the TL excitation (TLE) spectrum at room temperature there is no Ce3+:5d1 band (the lowest excited 5d level). However, in the TLE spectrum at 573 K, which corresponds to the onset temperature of luminescence quenching, a TLE band due to the Ce3+:5d1 excitation was observed at around 450 nm. On the basis of our observations we conclude that the luminescence quenching of YAG:Ce3+ at ...
270 citations
References
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
51,997 citations
TL;DR: The literature on 4f n ↔4f n −1 5d transitions of the trivalent lanthanides in inorganic compounds has been collected as mentioned in this paper from critically analyzing fd-excitation, absorption, reflection and df-emission spectra, values for the spectroscopic red shift of 5d levels and the stokes shift were determined.
853 citations
TL;DR: In this paper, the fluorescence of a number of new Ce3+activated phosphors is described and discussed, and conditions for visible Ce3−activated phosphor emission are indicated, viz., large crystal-field splittings (Y3Al5O12−Ce) or a large Stokes shift (SrY2O4•Ce).
Abstract: The fluorescence of a number of new Ce3+‐activated phosphors is described and discussed. Only host lattices with a sublattice consisting of trivalent lanthanide ions are used to avoid charge compensation of the Ce3+ ion. Usually the Ce3+ emission is in the near‐ultraviolet region. Y3Al5O12–Ce and SrY2O4–Ce, however, show emission in the visible region with a maximum in the green. Conditions for visible Ce3+ emission are indicated, viz., large crystal‐field splittings (Y3Al5O12–Ce) or a large Stokes shift (SrY2O4–Ce). In a number of cases we were able to observe all crystal‐field components of the excited 5d level of Ce3+. The cubic crystal‐field splitting of the 5d level varies strongly with host lattice from 7000 to 14 000 cm−1. The position of the center of the 5d levels in oxides is about 30% lower than in the free ion. For some phosphors we observed more than one emission band at room temperature. This is due to fluorescence from higher excited levels. Efficient energy transfer from Ce3+ to Cr3+ was observed in Y3Al5O12.
564 citations
TL;DR: In this paper, the possibilities of color tuning with the efficient LED phosphor Sr1−x−y−zCaxBaySi2O2N2:Euz2+ (0 ≤ x, y ≤ 1; 0.005 ≤ z ≤ 0.16) are investigated.
Abstract: Color point tuning is an important challenge for improving white light LEDs. In this paper, the possibilities of color tuning with the efficient LED phosphor Sr1−x−y−zCaxBaySi2O2N2:Euz2+ (0 ≤ x, y ≤ 1; 0.005 ≤ z ≤ 0.16) are investigated. The emission color can be tuned in two ways: by changing Eu2+ concentration and by substitution of the host lattice cation Sr2+ by either Ca2+ or Ba2+. The variation in the Eu2+ concentration shows a red shift of the emission upon increasing the Eu concentration above 2%. The red shift is explained by energy migration and energy transfer to Eu2+ ions emitting at longer wavelengths. Along with this (desired) red shift there is an (undesired) lowering of the quantum efficiency and the thermal quenching temperature due to concentration quenching. Partial substitution of Sr2+ by either Ca2+ or Ba2+ also results in a red-shifted Eu2+ emission. For Ca2+ this is expected and the red shift is explained by an increased crystal field splitting for Eu2+ on the (smaller) Ca2+ cation ...
551 citations
TL;DR: In this paper, the authors used a combinatorial approach where targeted single-crystal compositions are obtained by a flexible, time saving, and cost-effective crystal growth technique.
Abstract: The Ce-doped (LuyGd1–x)3(Gay,Al1–y)5O12 single crystals were grown by the micropulling down method. Their structure and chemical composition were checked by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) techniques. Optical, luminescent, and scintillation characteristics were measured by the methods of time-resolved luminescence spectroscopy, including the light yield and scintillation decay. Balanced Gd and Ga admixture into the Lu3Al5O12 structure provided an excellent scintillator where the effect of shallow traps was suppressed, the spectrally corrected light yield value exceeded 40 000 photons/MeV, and scintillation decay was dominated by a 53 ns decay time value which is close to that of Ce3+ photoluminescence decay. This study provides an excellent example of a combinatorial approach where targeted single-crystal compositions are obtained by a flexible, time saving, and cost-effective crystal growth technique.
459 citations