| 1. |
- Monemar, B, et al.
(författare)
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Magnetic properties of bound hole states for complex neutral defects in semiconductors
- 1986
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 36:3, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of an electron-hole pair bound to complex neutral defects in semiconductors are discussed and compared to experimental data for both direct- and indirect-bandgap materials. The properties of bound hole states for such defects are discussed in a general formalism, which avoids the generally inadequate effective-mass-like description often used in previous literature. In the case of low symmetry defects with a dominantly hole-attractive local potential the primary bound hole state is often nondegenerate and shows a spin-like character with a quenched angular momentum. This case has recently been demonstrated experimentally for a large number of defects in GaP and Si. A strong spin-orbit interaction may inhibit such a quenching so that the bound hole angular momentum is at least partly retained. This situation often prevails for complex defects in materials like CdTe and ZnTe, where the valence band spin-orbit splitting Δso is large. For electron-attractive central cell potentials, the bound hole state is generally effective-mass-like, and retains its anisotropic magnetic behaviour due to the hole angular momentum. Experimental data supporting this situation are also demonstrated, for both Si and compound semiconductors.
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| 2. |
- Sendova-Vassileva, M, et al.
(författare)
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Depth dependence of photoluminescence and chemical bonding in porous silicon
- 1999
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Ingår i: Journal of Luminescence. - 0022-2313 .- 1872-7883. ; 80:1-4, s. 179-182
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Tidskriftsartikel (refereegranskat)abstract
- Porous silicon (PS) is studied by stepwise peeling of the surface layer to clarify the non-uniformity in the photoluminescence (PL) and correlate it with the in-depth chemical bonding and structure of the 30 μm thick layer. The PL intensity grows by an order of magnitude after the peeling off of the first 10 μm and decreases five times in the next 5 μm while the peak maximum position shifts from 730 to 800 nm. X-ray photoelectron spectroscopy (XPS) measurements show that Si–Si and Si–O bonds are present both on the surface and below, and the preferential oxidation state of silicon changes from 3+ and 4+ on the surface to 1+ and 2+ below 10 μm. Using Raman spectroscopy silicon nanocrystals are shown to exist. Their mean size can be estimated at about 3 nm. These results show that the strongest PL comes from a region in the PS layer where silicon nanocrystallites are surrounded by oxides with a low level of oxidation and not from the strongly oxidized surface layer.
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| 3. |
- Auzel, Francois, et al.
(författare)
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Homogeneous line width of rare-earth-doped glasses for levels in a Stark level ladder : A new simple rule
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 122:1-2, s. 453-455
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Tidskriftsartikel (refereegranskat)abstract
- Concentrating on higher Stark states in multiplet ladders of lanthanide-doped glasses, we show that at 10 K, the homogeneous widths along Stark ladders vary quasi-linearly with the energy position in the ladder.Assuming that the mechanisms creating the homogeneous widths are first-order processes, either direct processes or two-phonon nonradiative transitions, the observed behavior is simply explained by the fact that energy separations between Stark levels for usual glasses are less, i.e., not far from kT(D), the Debye energy. This in turn provides quasi-equal phonon transition probabilities between individual Stark states. A simple theoretical relationship is derived and compared with experiments.
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| 4. |
- Auzel, Francois, et al.
(författare)
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Photon trapping in ruby and lanthanide-doped materials: Recollections and revival
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 125:1-2, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- After some recollections of phonon and photon trapping in ruby, a critical review of this effect of renewed interest in trivalent lanthanide-doped materials is presented showing that the two independent derivations taking their roots in the work of Milne for gases and of Birks for organic scintillators are practically described by an analogous phenomenological equation when re-absorption is weak. The problem of obtaining "extrinsic" quantum efficiency larger than one is briefly discussed.
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| 5. |
- Bano, Nargis, et al.
(författare)
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Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC
- 2010
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Ingår i: Journal of Luminescence. - : Elsevier Science B.V., Amsterdam.. - 0022-2313 .- 1872-7883. ; 130:6, s. 963-968
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Tidskriftsartikel (refereegranskat)abstract
- Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors.
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| 6. |
- Basiev, T. T., et al.
(författare)
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Luminescent nanophotonics and advanced solid state lasers
- 2013
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 133, s. 233-243
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Tidskriftsartikel (refereegranskat)abstract
- In this review, authors present their latest findings in luminescence quenching kinetics theory and advanced solid state laser experiments. Luminescence quenching kinetics is a popular and exceptionally useful tool to analyze the nanosized luminophores and laser material nanostructure. Quenching kinetics may be multistage, some stages having a complex, not exponential, form. It is often the case for modern laser materials, which are nanostructurized, and for particular cases of energy transfer (such as cooperative down-conversion). We present compact and easy-to-use analytical expressions and computer simulation for various cases of nonexponential quenching kinetics: migration-accelerated quenching in bulk material; cooperative luminescence quenching in bulk material; and two extreme cases of energy transfer in nanoparticles - static and with superfast migration (both including cooperative case of luminescence quenching in ensembles of acceptors comprised of two-, three-, and more particles). We also review the most perspective laser experiments lately performed in our laboratory, including those on fluoride laser nanoceramics and materials for middle infra-red lasers. (c) 2011 Elsevier B.V. All rights reserved.
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| 7. |
- Basieva, Irina, et al.
(författare)
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Static cooperative luminescence quenching in nanoparticles
- 2014
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 151, s. 88-92
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Tidskriftsartikel (refereegranskat)abstract
- In nanoparticles (NPs) static quenching of luminescence may be slower than in bulk media due to the space restrictions on acceptor location. Many-body cooperative quenching (manifesting itself as, e.g., down-conversion) occurs when the donor energy is transferred to two-, three-, or more particles (a cooperative acceptor) at once. Random distribution of acceptor particles in diluted media accounts for the non-exponential form of the kinetics. When the analytical expression for the kinetics form is known, it can be fitted to the experiment in order to find various micro- and macro-quenching parameters of the luminescent material. In this paper, we present an analytical law for cooperative quenching kinetics in NPs at longer time. Its clear and compact form reflects the fact that, on average, donors located on the surface of NPs are the last to decay having acceptors on one side only. We compared the resulting formula with the Monte-Carlo computer simulation, and they show good agreement. (C) 2014 Elsevier B.V. All rights reserved.
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| 8. |
- Echresh, Ahmad, et al.
(författare)
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High photocurrent gain in NiO thin film/M-doped ZnO nanorods (M = Ag, Cd and Ni) heterojunction based ultraviolet photodiodes
- 2016
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Ingår i: Journal of Luminescence. - : ELSEVIER SCIENCE BV. - 0022-2313 .- 1872-7883. ; 178, s. 324-330
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Tidskriftsartikel (refereegranskat)abstract
- The thermal evaporation method has been used to deposit p-type NiO thin film, which was combined with hydrothermally grown n-type pure and M-doped ZnO nanorods (M=Ag, Cd and Ni) to fabricate a high performance p-n heterojunction ultraviolet photodiodes. The fabricated photodiodes show high rectification ratio and relatively low leakage current. The p-NiO/n-Zn0.94Ag0.06O heterojunction photo diode displays the highest photocurrent gain (similar to 1.52 x 10(4)), a photoresponsivity of similar to 4.48 x 10(3) AW(-1) and a photosensitivity of similar to 13.56 compared with the other fabricated photodiodes. The predominated transport mechanisms of the p-n heterojunction ultraviolet photodiodes at low and high applied forward bias may be recombination-tunneling and space charge limited current, respectively. (C) 2016 Elsevier B.V. All rights reserved.
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| 9. |
- Echresh, Ahmad, et al.
(författare)
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Light emitting diode based on n-Zn0.94M0.06O nanorods/p-GaN (M= Cd and Ni) heterojunction under forward and reverse bias
- 2015
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 160, s. 305-310
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we report on the improvement in the optoelectronic properties of n-ZnO nanorods/p-GaN heterojunction. This was achieved by doping the ZnO with cadmium (Cd) and nickel (Ni). The ZnO and Zn0.94M0.06O nanorods grown hydrothermally on the p-GaN substrate were used to fabricate the light emitting diodes (LEDs). Structural measurement revealed that nanorods with wurtzite structure having a preferential orientation along the (002) c-axis. The UV-vis spectra show that the optical band gap of Zn0.94M0.06O nanorods is decreased in comparison to ZnO nanorods. Electrical measurements of the fabricated LEDs show an obvious rectifying behaviour with low threshold voltage. Electroluminescence (EL) characteristics of LEDs operated at forward and reverse bias were investigated. The EL spectra under forward bias show that doping ZnO nanorods with Cd and Ni led to an intensity enhancement of the broad peak in the visible region while the blue peak originating from the p-GaN substrate remains almost unaffected. The effect of doping was to reduce the valence band offsets and consequently more hole injection has occurred leading to the observed enhancement of the broad band in the visible region. Under reverse bias all heterojunction LEDs show the blue light emission peak originating from the p-GaN substrate.
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| 10. |
- Enrichi, Francesco, et al.
(författare)
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Visible to NIR downconversion process in Tb3+-Yb3+ codoped silica-hafnia glass and glass-ceramic sol-gel waveguides for solar cells
- 2018
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 193, s. 44-50
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of photovoltaic solar cells is strongly related to the spectral absorption and photo-conversion properties of the cell's active material, which does not exploit the whole broadband solar spectrum. This mismatch between the spectrum of the solar light and the wavelength dependent cell's response can be partially overcome by using luminescent conversion layers in front or in the back of the solar cell. In this paper, the investigation of Tb3+-Yb3+ co-doped SiO2-HfO2 glass and glass-ceramic waveguides is presented. Due to a down-conversion process based on cooperative energy transfer between one Tb3+ ion and two Yb3+ ions, a blue photon at 488 nm can be divided in two NIR photons at 980 nm. Films with different molar concentrations of rare earths, up to a total amount of [Tb+Yb] = 15%, were prepared by a sol-gel route, using dip-coating deposition on SiO2 substrates. For all the films, the molar ratio [Yb]/[Tb] was taken equal to 4. The comparison of the energy-transfer efficiency between Tb3+ and Yb3+ ions in the glass and in the glass-ceramic materials demonstrated the higher performance of the glass-ceramic, with a maximum quantum transfer efficiency of 179% for the highest rare earth doping concentration. Moreover, experimental results and comparison with proper rate equations modelling showed a linear dependence of the photoluminescence emission intensity for the Yb3+ ions 2F5/2 → 2F7/2 transition at 980 nm on the excitation power, indicating a direct transfer process from Tb3+ to Yb3+ ions. The reported waveguides could find applications not only as downconverting filters in transmission but also as efficient solar concentrators in the near-IR spectral region
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