| 1. |
- Duteil, F., et al.
(författare)
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Er/O doped Si1-xGex alloy layers grown by MBE
- 2001
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 17:1-2, s. 131-134
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Silicon-based light emitting diodes (LEDs) containing an Er/O-doped Si1-xGex active layer have been studied. The structures were grown by molecular beam epitaxy (MBE), with Er and O concentrations of 5 × 1019 and 1 × 1020 cm-3, respectively, using Er and silicon monoxide sources. The microstructure has been studied by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy, and it is found that Er/O-doped Si0.92Ge0.08 layers of high crystalline quality, can be obtained. Electroluminescence (EL) measurements have been performed on reverse-biased Er/O doped diodes both from the surface and from the edge and the emission at 1.54 µm associated with the Er3+ ions has been studied at 300 K and lower temperatures. To evaluate the possibility to use a Si1-xGex layer for waveguiding in Si-based optoelectronics, studies of the refractive index n of strained Si1-xGex as a function of the Ge concentration have been done by spectroscopic ellipsometry in the range 0.3-1.7 µm. At 1.54 µm the refractive index increases monotonically with the Ge concentration up to n = 3.542 for a Ge concentration of 21.3%. © 2001 Elsevier Science B.V.
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| 2. |
- Inganäs, Olle, et al.
(författare)
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Optical emission from confined poly(thiophene) chains
- 1998
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 9:1-4, s. 104-108
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the stages of the luminescence processes in substituted and soluble poly(thiophenes), using results from determinations of absolute quantum yields of photoluminescence, fast pump-probe experiments and microcavity devices. Enhancement of the quantum yield of photoluminescence, with poly(thiophenes) in the solid state, call be obtained by dispersing the conjugated chain in a molecularly dispersed polymer blend, or by adding side chains designed for forcing the conjugated main chains apart. At the wavelength of stimulated emission, we observe a narrow bandwidth emission in the high-Q one-dimensional microcavity devices prepared by sandwiching two dielectric mirrors around a thin polymer film, A strong enhancement of the power efficiency is observed at a pump power of 1 mu W/cm(2), but does not conclusively show lasing characteristics. (C) 1998 Elsevier Science B.V.
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| 3. |
- Ni, Wei-Xin, et al.
(författare)
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1.54 µm light emitting devices based on Er/O-doped Si layered structures grown by molecular beam epitaxy
- 2001
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 17:1-2, s. 65-69
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Two types of Si:Er light emitting devices have been processed and characterized with an aim to efficiently use hot electrons for impact excitation. One is a p+-SiGe/i-Si/n-Si:Er:O/n+-Si tunneling diode with a design favoring electron tunneling from the SiGe valence band to the Si conduction band and subsequent acceleration. Another type of Si:Er light emitters is based on a heterojunction bipolar transistor (HBT) structure containing an Er-doped active layer in the collector. In these devices, one can introduce hot electrons from the HBT emitter in a controlled way with a collector bias voltage prior to the avalanche breakdown to improve the impact excitation efficiency. Intense electroluminescence was observed at 300 K at low current (0.1 A cm-2) and low bias (3 V). An impact cross-section value of 1 × 10-14 cm2 has been estimated, which is a 100-fold increase compared with the values reported from any other type of Er-doped LEDs. © 2001 Elsevier Science B.V.
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| 4. |
- Pitois, Claire, et al.
(författare)
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Fluorinated dendritic polymers and dendrimers for waveguide applications
- 2003
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 21:1-3, s. 499-506
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Tidskriftsartikel (refereegranskat)abstract
- I Fluorinated hyperbranched polymers and dendrimers with low optical losses and functionality to modify refractive index and add a cross-linking unit were developed. The results of refractive index. measurements indicate a tunability of the refractive index between approximately 1.5 and 1.6, and optical losses below 0.5 dB/cm at 1550 nm. Dendrimers with similar, surface group structure and possibility to surface functionalization were prepared using a lanthanide. cation as focal point. Results on luminescent properties in the NIR and IR regions were measured for lanthanide ions such as Nd3+ and Er3+, showing characteristic emission bands at 1.06, 1.3 and 1.5 mum. The associated absorption and excitation spectra were found similar to those of the corresponding ions in optical glasses.
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| 5. |
- Rönnow, Daniel, et al.
(författare)
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Surface Roughness Effects in Ellipsometry: Comparison of Truncated Sphere and Effective Medium Models
- 1995
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 4:6, s. 815-821
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the applicability of effective medium models for describing the effects of surface roughness on ellipsometric data. The ellipsometric parameters of a model surface composed of truncated spherical bumps on a substrate were calculated and compared to the Bruggeman effective medium theory. It is possible to fit the model calculations with the Bruggeman theory. However, the thickness and volume fraction of the effective medium layer describing the surface roughness do not correspond to the physical height and volume fraction of the bumps on the model surface.
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| 6. |
- Strömme, Maria, et al.
(författare)
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Optical constants of sputtered hafnium nitride films. Intra- and interband contributions
- 1995
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 4:5, s. 629-639
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Tidskriftsartikel (refereegranskat)abstract
- Transparent and opaque films of hafnium nitride have been prepared by reactive magnetron sputtering in an argon-nitrogen atmosphere. The films were deposited upon heated Coming glass substrates with a deposition rate of about 2.1 nm/s. The optical constants of the films were calculated using Kramers-Kronig integration and ellipsometry for the opaque samples and a combined method for transparent samples. Detailed observation of the thickness variation in the optical constants revealed a clear trend: larger n-values and smaller k-values in the VIS-and NIR-range for thinner films. This was analysed within the framework of the classical Drude model and found to be an effect of shorter relaxation time for thinner films. The effect is as large as a factor of three in the film thickness interval 15–380 nm. The optical effective mass of the d-electrons was found to be in the interval 0.82–0.95 of the free electron mass, which is significantly lower than in TiN but similar to ZrN. The interband contribution to ϵ2(ω) was obtained by subtraction of the Drude part from the experimental dielectric function. It exhibits a sharp increase for λ < 400 nm, indicating the threshold for interband transistion.
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| 7. |
- Valenta, J., et al.
(författare)
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Electroluminescence microscopy and spectroscopy of silicon nanocrystals in thin SiO2 layers
- 2001
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Ingår i: Optical materials (Amsterdam). - 0925-3467 .- 1873-1252. ; 17:02-jan, s. 45-50
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Tidskriftsartikel (refereegranskat)abstract
- Stable continuously operable electroluminescent diodes have been fabricated by Sii-ion implantation and annealing of thin SiO2 layers on a silicon substrate. The external quantum efficiency of the device is reaching 3 x 10(-5) for the best diodes. Electroluminescence (EL) emission band is wide and centered at 800 nm. EL is due to radiative recombination of tunneling carriers in Si-nanocrystals(NC) with small contribution of oxide defects (peak at 650 nm). EL images reveal inhomogeneous emission structures on the micrometer scale. Mainly, a small number of bright spots with diffraction limited size (similar to 600 nm) with a homogeneous background are observed and their EL spectra measured using an imaging spectrometer with a liquid-nitrogen-cooled CCD camera. The bright EL spots originate from the efficiently excited emission of oxide defects and/or emission of a few (possibly single) Si-NC, most likely at places with locally increased current. The low efficiency is probably a consequence of current tunneling through optically inactive nanocrystals or defects in a very thin oxide layer.
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| 8. |
- Almeida, J. M. P., et al.
(författare)
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Femtosecond laser processing of glassy and polymeric matrices containing metals and semiconductor nanostructures
- 2013
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 35:12, s. 2643-2648
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Tidskriftsartikel (refereegranskat)abstract
- Tailoring properties of materials by femtosecond laser processing has been proposed in the last decade as a powerful approach for technological applications, ranging from optics to biology. Although most of the research output in this field is related to femtosecond laser processing of single either organic or inorganic materials, more recently a similar approach has been proposed to develop advanced hybrid nanomaterials. Here, we report results on the use of femtosecond lasers to process hybrid nanomaterials, composed of polymeric and glassy matrices containing metal or semiconductor nanostructures. We present results on the use of femtosecond pulses to induce Cu and Ag nanoparticles in the bulk of borate and borosilicate glasses, which can be applied for a new generation of waveguides. We also report on 3D polymeric structures, fabricated by two-photon polymerization, containing Au and ZnO nanostructures, with intense two-photon fluorescent properties. The approach based on femtosecond laser processing to fabricate hybrid materials containing metal or semiconductor nanostructures is promising to be exploited for optical sensors and photonics devices.
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| 9. |
- Bagheri, Niusha, et al.
(författare)
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Change in the emission saturation and kinetics of upconversion nanoparticles under different light irradiations
- 2019
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 97
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Tidskriftsartikel (refereegranskat)abstract
- Nd3+-sensitized upconversion nanoparticles (UCNPs) can be excited by both 980 and 808 nm light, which is regarded as a particularly advantageous property of these particles. In this work, we demonstrate that the nanoparticles can exhibit significantly different response when excited at these two excitation wavelengths, showing dependence on the intensity of the excitation light and the way it is distributed in time. Specifically, with 808 nm excitation saturation in the emitted luminescence is more readily reached with increasing excitation intensities than upon 980 nm excitation. This is accompanied by delayed upconversion luminescence (UCL) kinetics and weaker UCL intensities. The different luminescence response at 808 and 980 nm excitation reported in this work is relevant in a manifold of applications using UCNPs as labels and sensors. This could also open new possibilities for multi-wavelength excitable UCNPs for upconversion color display and in laser-scanning microscopy providing selective readouts and sub-sectioning of samples.
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| 10. |
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