Thermoluminescence (TL) or thermally stimulated luminescence (TSL) spectroscopy is based on liberating charge carriers from traps in the bandgap by providing enough thermal energy to overcome the ...potential barrier of the traps. It provides a powerful tool to measure the positions of the localized states/traps in the bandgap. Despite that, its applications in semiconductors are very limited. Herein, the basics of TL spectroscopy and the recent advances in the technique with focus on cryogenic thermally stimulated photoemission spectroscopy (C‐TSPS) which extends TL measurements to cryogenic regime and allows the detection of very low concentrations of shallow and deep localized states is discussed. One goal herein is to introduce the reader to the use of TL and C‐TSPS in the characterization of semiconductors, explaining how it can be applied and demonstrating its advantages as a powerful tool for measuring shallow donor/acceptor ionization energies in semiconductors and as a method for characterizing compensating defects. The article also discusses interesting potential applications of C‐TSPS in new research areas such as corrosion and formation of oxide layers on metal surfaces.
Herein, a new perspective is provided on how to use thermoluminescence as a powerful research tool for semiconductors demonstrating its capabilities in measuring donor/acceptor ionization energies and densities and presenting new instrumentation development that expands its applications to new areas and guides the research efforts in understanding and controlling the electronic and photonic properties of materials.
Persistent photoconductivity was observed in strontium titanate (SrTiO(3)) single crystals. When exposed to sub-bandgap light (2.9 eV or higher) at room temperature, the free-electron concentration ...increases by over 2 orders of magnitude. After the light is turned off, the enhanced conductivity persists for several days, with negligible decay. From positron lifetime measurements, the persistent photoconductivity is attributed to the excitation of an electron from a titanium vacancy defect into the conduction band, with a very low recapture rate.
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•Effective regulation of Ce:YAG ceramics by Sc3+ substituting in Al3+ site.•High thermal stability (~6% loss, 150 °C) and high quantum efficiency of 84.2%.•Spectral property of ...ceramics presented a 21 nm blueshift and decreased Stokes shift.•Tunable optoelectronic performance for ceramic-based WLED/LD.
Realizing the high brightness solid-state lighting with the emission spectra similar to that of sun light is significantly challenged by the inherent deficiency of the luminescence spectrum and thermal robustness in the single sturctured Ce3+:Y3Al5O12 (Ce:YAG) transparent ceramic (TC). In this study, based on the idea of energy band engineering, the energy splitting intensity of 5d level and the energy gap between the ground band and the 5d1 energy level of Ce3+ ion in Ce:YAG TC were effectively modified via Sc doping. A series of Ce:Y3Al5−xScxO12 (Ce:YASG) TCs were fabricated with impressive properties, showing a decreased stokes shift and a distinct blue-shift (541 → 520 nm) with broadened full width in emission spectra. Particularly, the prepared TCs exhibited a desired thermal stability (only ~6% luminescent intensity loss at 150 °C) and high internal quantum efficiency (IQE) of 84.2%. The optimal composition between Ce3+ and Sc3+ ions was investigated by constructing the Ce:YASG and (Y1−yCey)3Al4ScO12 (YCASG) TC-based white LEDs/LDs in a remote excitation mode. Both the luminous efficiency of radiation (LER) as high as 218 lm/W and tunable color from pale-green (pale-white) to yellowish white (pale-green) region were obtained. Therefore, the Ce:YASG TC is a highly promising color conversion material for high power lighting and displaying applications in the future.
In this work, a small amount of CaO single dopant was adopted to realize the densification and microstructure control of fine grained YAG ceramic with excellent optical quality, by a simple ...solid‐state reaction and one‐step vacuum sintering method. Then, highly transparent YAG ceramics (T = 84.4% at 1064 nm) were obtained just after vacuum sintering at 1820°C for 8 hours. The average grain size was only 2.7 μm, when the total amount of CaO was as low as 0.045 wt%. The effect of CaO on the microstructural evolution and optical property of the as‐fabricated YAG ceramics was systematically investigated in detail. It was found that CaO dopant promoted both densification and grain growth of YAG ceramics when the sintering temperature was lower than 1660°C, however, it dramatically inhibited grain growth when the sintering temperature was further increased.
High sinterability nano-Y
2
O
3
powders for transparent ceramics were successfully synthesized via the decomposition of hydroxyl-carbonate precursors from spray coprecipitation. The chemical ...composition of the precursor was determined as Y(CO
3
)(OH)·
n
H
2
O (
n
= 1–1.5), and it was evolved into Y
2
O
3
particles with clear facets after calcination with the assistance of sulfate. Two dispersion mechanisms, “absorption” and “intercalation,” were proposed to work together to provide the dispersion effect. Microstructural and optical characterization of powders and as-fabricated transparent ceramics was employed to evaluate the sintering behavior of powders. The nanopowders calcined at 1250 °C had weakly agglomerated morphology with the mean particle size of ~140 nm and exhibited excellent sinterability. The in-line transmittance of Y
2
O
3
ceramic of 1 mm thickness that was vacuum sintered at 1800 °C for 8 h without any sintering additives reached 78.7% at 1064 nm.
Abstract
Advancement of optoelectronic and high-power devices is tied to the development of wide band gap materials with excellent transport properties. However, bipolar doping (n-type and p-type ...doping) and realizing high carrier density while maintaining good mobility have been big challenges in wide band gap materials. Here P-type and n-type conductivity was introduced in β-Ga
2
O
3
, an ultra-wide band gap oxide, by controlling hydrogen incorporation in the lattice without further doping. Hydrogen induced a 9-order of magnitude increase of n-type conductivity with donor ionization energy of 20 meV and resistivity of 10
−4
Ω.cm. The conductivity was switched to p-type with acceptor ionization energy of 42 meV by altering hydrogen incorporation in the lattice. Density functional theory calculations were used to examine hydrogen location in the Ga
2
O
3
lattice and identified a new donor type as the source of this remarkable n-type conductivity. Positron annihilation spectroscopy measurements confirm this finding and the interpretation of the experimental results. This work illustrates a new approach that allows a tunable and reversible way of modifying the conductivity of semiconductors and it is expected to have profound implications on semiconductor field. At the same time, it demonstrates for the first time p-type and remarkable n-type conductivity in Ga
2
O
3
which should usher in the development of Ga
2
O
3
devices and advance optoelectronics and high-power devices.
To efficiently capture the energy of the nuclear bond, advanced nuclear reactor concepts seek solid fuels that must withstand unprecedented temperature and radiation extremes. In these advanced ...fuels, thermal energy transport under irradiation is directly related to reactor performance as well as reactor safety. The science of thermal transport in nuclear fuel is a grand challenge as a result of both computational and experimental complexities. Here we provide a comprehensive review of thermal transport research on two actinide oxides: one currently in use in commercial nuclear reactors, uranium dioxide (UO2), and one advanced fuel candidate material, thorium dioxide (ThO2). In both materials, heat is carried by lattice waves or phonons. Crystalline defects caused by fission events effectively scatter phonons and lead to a degradation in fuel performance over time. Bolstered by new computational and experimental tools, researchers are now developing the foundational work necessary to accurately model and ultimately control thermal transport in advanced nuclear fuels. We begin by reviewing research aimed at understanding thermal transport in perfect single crystals. The absence of defects enables studies that focus on the fundamental aspects of phonon transport. Next, we review research that targets defect generation and evolution. Here the focus is on ion irradiation studies used as surrogates for damage caused by fission products. We end this review with a discussion of modeling and experimental efforts directed at predicting and validating mesoscale thermal transport in the presence of irradiation defects. While efforts in these research areas have been robust, challenging work remains in developing holistic tools to capture and predict thermal energy transport across widely varying environmental conditions.
β-phase titanium pentoxide (β-Ti3O5) has great potential applications in sensors, electrodes and laser devices, due to its unique phase-transforming behaviors. However, just this reversible phase ...transition behaviors between λ and β phases made its high purity preparation be challenging, and the high energy consumption of present industrialized method also limited the high-level applications of β-Ti3O5. In this work, a novel carbothermal reduction method has been acquired to produce highly pure β-Ti3O5 compacts from titanium dioxide “wrapped” by phenolic resin served as carbon source. Their phase and microstructure evolutions during the whole reaction process were systematically characterized under the assistance of Rietveld refinement and SEM images. The highly active pyrolytic carbon of phenolic resin could deposit on the surface of TiO2 and this compacted state could promote the generated CO to accelerate the reaction process and decrease the addition of reductant, simultaneously. The reduction sequences were TiO2→ Ti4O7→ Ti3O5→ Ti2O3. The weight ratio of phenolic to precursor of 9.0% could achieve the pure β-Ti3O5 as high as 98.06% under the calcination temperature of 1250 °C for 4 h. This work provided a novel and industrialized route to prepare β-Ti3O5 for applications in sensor and electrode in electrochemical reactions.
•A novel carbon thermal reduction for the high purity β-Ti3O5.•Reduction mechanism of phenolic resin and phase evolution of TiO2.•Carbothermal reduction for the low cost and high efficiency preparation of oxides.
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