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Cuprous oxide (Cu2O) thin films were grown via radio frequency sputtering deposition at various temperatures. The dielectric functions and luminescence properties of the Cu2O thin films were measured using spectroscopic ellipsometry and photoluminescence, respectively. High-energy peaks were observed in the photoluminescence spectra. Several critical points (CPs) were found using second derivative spectra of the dielectric functions and the standard critical point model. The electronic band structure and the dielectric functions were calculated using density functional theory, and the CP energies were estimated to compare with the experimental data. We identified the high-energy photoluminescence peaks to quasi-direct transitions which arose from the granular structures of the Cu2O thin films. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) properties have been studied for Ge-doped ZnO films grown on Si wafers by RF-magnetron sputtering. A PL line, named as G line, appears at 3.324 eV by Ge doping and is attributed to Ge suboxide states including GeO color centers. As Ge concentration (nGe) increases, the intensities of free-exciton-, and neutral-donor-bound-exciton-, two-electron-satellite-, and G-PL lines increase, while those of their phonon replicas decrease. By Ge doping, no-phonon line deconvoluted from the near-band-edge (NBE) PL at 300 K is enhanced, but its LO phonon replicas are reduced, resulting in the enhancement of the NBE PL with its reduced bandwidth. It is suggested that these results are due to the increase of the Ge suboxide states with increasing nGe, which is also confirmed by the analysis of the Ge 3d core-level spectra by x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

Studies the temperature and power dependence of the photoluminescence spectra which arose from the dislocations at the hetero-interface of very thin and partially strained silicon germanium alloys grown on silicon substrates. Experimental details; Results and discussion; Conclusions.

Optical and electrical characteristics of ZnO films co-implanted with O and As ions have been investigated by photoluminescence (PL), Hall-effect, and current-voltage (I-V) measurements. 100-nm-thick ZnO films grown on n-type Si (100) wafers by RF sputtering have been implanted with various fluences of 30 keV O and 100 keV As ions at room temperature, and subsequently annealed at 800 °C for 20 min in a N2 ambient. The dually-implanted ZnO films show stable p-type characteristics for particular implant combinations, consistent with the observation of dominant PL peaks at 3.328 and 3.357 eV that are associated with the acceptor levels. For these dually-implanted p-type ZnO films/n-type Si diodes, the I-V curves show rectifying p-n junction behavior. Other singly (As)- or dually-implanted samples show n-type or indeterminable doping characteristics. These results suggest that O implantation plays a key role in forming p-type ZnO films by reducing the oxygen vacancy concentration and facilitating the formation of As-related acceptors in ZnO. [ABSTRACT FROM AUTHOR]

Ge nanocrystals (NCs) are shown to form within HfO2 at relatively low annealing temperatures (600¿700 °C) and to exhibit characteristic photoluminescence (PL) emission consistent with quantum confinement effects. After annealing at 600 °C, sample implanted with 8.4*1015 Ge cm-2 show two major PL peaks, at 0.94 and 0.88 eV, which are attributed to no-phonon and transverse-optical phonon replica of Ge NCs, respectively. The intensity reaches a maximum for annealing temperatures around 700 °C and decreases at higher temperatures as the NC size continues to increase. The no-phonon emission also undergoes a significant redshift for temperatures above 800 °C. For fluences in the range from 8.4*1015 to 2.5*1016 cm-2, the average NC size increases from ¿13.5±2.6 to ¿20.0±3.7 nm. These NC sizes are much larger than within amorphous SiO2. Implanted Ge is shown to form Ge NCs within the matrix of monoclinic (m)-HfO2 during thermal annealing with the orientation relationship of [101]m-HfO2//[110]Ge NC. [ABSTRACT FROM AUTHOR]

P-n junction GaN light-emitting diodes (LEDs) were fabricated using Ga-doped ZnO (GZO) films as electrical contacts and characterized by electroluminescence (EL) and current-voltage (I-V) measurements. GaN p-n epilayers with a total thickness of ~6 μm were grown on c-plane (0001) sapphire substrates by metal-organic chemical vapor deposition. Half region of the p-GaN layer was etched until the n-GaN layer was exposed, and 100-nm-thick GZO contacts were deposited on the p- and n-GaN layers by RF sputtering with varying Ga concentration ( n) from 1 to 5 mol%. Based on the results of Hall effect, photoluminescence (PL), and X-ray diffraction (XRD), the GZO films were expected to act as best electrical contacts for the LEDs at n = 2 mol%. Under forward-bias conditions, the I-V curves showed diode characteristics except n = 5 mol%, and the leakage current was minimized at n = 2 mol%. Two dominant EL peaks of ultraviolet and yellow emissions were observed at ~376 and ~560 nm, and attributed to near-band-edge- and defect-related radiative transitions, respectively. At n = 2 mol%, the UV EL showed markedly large intensities for all injection currents, consistent with the results of Hall effect, PL, I-V, and XRD. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) and Raman scattering have been used to study the defect-related growth of Ge nanocrystals during annealing of Ge+-implanted SiO2 films. Under 250 nm (∼5 eV) photon excitation, the as-implanted sample has two strong PL bands peaked at 288 nm (4.3 eV) and 395 nm (3.1 eV), which are denoted as α- and β-bands, respectively. The (β/α) ratio increases with increasing implant dose. The position and linewidth of the crystalline-Ge Raman peak found approximately 300 cm−1 after annealing at 550 °C remain almost unchanged by further increasing the annealing temperature up to 1100 °C. The annealing behaviours of Raman peaks including the extra 229, 435/485 cm−1 ones, characteristic of amorphous Ge, Ge–Si intermixing, respectively, are closely related to those of both the absolute and relative (β/α) intensities of the α- and β-bands. These are discussed with reference to the Ge-related oxygen deficient defects in the films. [Copyright &y& Elsevier]

SiO1.2/SiO2 multilayers were grown on n-type (100) Si wafers by ion beam sputtering and subsequently annealed at 1100 °C to form SiO2-embedded Si (S-Si) nanocrystals (NCs). The SiO2 matrix was then removed from S-Si NCs by chemical treatments to prepare freestanding Si (F-Si) NCs. The photoluminescence (PL) peak of F-Si NCs at ∼657 nm (1.89 eV) is blue-shifted with respect to that of S-Si NCs at ∼816 nm (1.52 eV). The peak shift of ∼0.37 eV is much larger than what is expected by the quantum confinement effect. The PL lifetime of F-Si NCs (∼3 ns) is much shorter than that of S-Si NCs (∼50 μs). Possible physical mechanisms are discussed to explain the origin of the fast PL band found in F-Si NCs. [ABSTRACT FROM AUTHOR]

A band of ∼1.6 nm diameter Si nanocrystals (NCs) has been prepared at a depth of about 5 nm within SiO2 by atomic-layer deposition of 2 nm amorphous Si on 5 nm SiO2 and subsequent thermal oxidation at 900 °C. After 4 h light exposure of 5.66 W/cm2, photoluminescence (PL) spectrum of the Si NCs is almost 60 times enhanced with its peak blueshifted by about 30 nm. The enhancement rate of the PL intensity with illumination time increases as the oxidation time increases. The PL intensity and its peak wavelength are partially recovered by annealing the samples at 440 K for 1 h, suggesting the effect is metastable. It is proposed that the anomalous light-induced effect is originated from the defect states at the Si NCs/SiO2 interfaces. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL), photoluminescence, and transmission electron microscopy have been used to study the light-emitting and structural properties of (1&1bar;02) sapphire implanted with 30-key Si ions and subsequently annealed at temperatures up to 1100°C. This procedure creates oriented Si crystallites with diameters in the range 4-5 nm together with extended defects parallel to the (0001) planes of (1&1bar;02) Al2O3. Several CL hands found in Si--implanted Al2O3(Al2O3:Si-) before and/or after annealing are compared with those from O- and Al--implanted samples. These and related experiments, including annealing temperature and implant dose dependence, suggest that a yellow CL band (2.16 eV/574 nm) from annealed Al2O3:Si- is nanocrystal related, while others are defect related. [ABSTRACT FROM AUTHOR]

A significant enhancement of photoluminescence (PL) intensity is observed in microdisks of 0.5 and 1 μm diam, which have been fabricated from Si/Ge/Si single quantum wells (SQWs) grown by molecular-beam epitaxy. The three major PL peaks found at 0.972, 0.957, and 0.920 eV are identified as a no-phonon transition of localized exciton, associated transverse-acoustical, and transverse-optical phonon replicas in Si, respectively. It is suggested that the formation of microdisks from the Si/Ge/Si SQWs enhances the intrinsic PL transitions significantly by suppressing the impurity-related ones. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract We first report highly-flexible and -stable deep-ultraviolet (DUV) photodiodes (PDs) by employing graphene (GR) quantum dots (GQDs) sandwiched between top/bottom GR layers on polyethylene terephthalates (PETs). Here, 3-aminopropyl triethoxysilane is inserted between the bottom GR and the PET substrate to enhance the bending stabilities without degradation or delamination by the chemical bonding. GQDs of ∼5 nm diameter are proved to be well formed on the bottom GR by various structural and optical analysis tools including high-resolution transmission electron microscopy, Raman scattering, and photoluminescence. The DUV PDs exhibit 10 photo-/dark-current ratio, 0.1 AW-1 responsivity (R), and 1.1 × 1013 cm Hz1/2/W detectivity at a wavelength of 254 nm. In addition, the R is reduced by only 13% even after 1000-times repeated bending tests at a bending curvature of 4 mm, and is almost consistent during the operations for 1000 h under ambient conditions. Highlights • First report of flexible deep UV photodiodes by employing graphene quantum dots. • 0.1 AW-1 responsivity and 1.1 × 1013 cm Hz1/2/W detectivity is achieved. • Stability maintaining ∼87% of initial responsivity after 1000 bending cycles. [ABSTRACT FROM AUTHOR]

Ge nanocrystals (NCs) are shown to form within HfO2 at relatively low annealing temperatures (600¿700 °C) and to exhibit characteristic photoluminescence (PL) emission consistent with quantum confinement effects. After annealing at 600 °C, sample implanted with 8.4*1015 Ge cm-2 show two major PL peaks, at 0.94 and 0.88 eV, which are attributed to no-phonon and transverse-optical phonon replica of Ge NCs, respectively. The intensity reaches a maximum for annealing temperatures around 700 °C and decreases at higher temperatures as the NC size continues to increase. The no-phonon emission also undergoes a significant redshift for temperatures above 800 °C. For fluences in the range from 8.4*1015 to 2.5*1016 cm-2, the average NC size increases from ¿13.5±2.6 to ¿20.0±3.7 nm. These NC sizes are much larger than within amorphous SiO2. Implanted Ge is shown to form Ge NCs within the matrix of monoclinic (m)-HfO2 during thermal annealing with the orientation relationship of [101]m-HfO2//[110]Ge NC. [ABSTRACT FROM AUTHOR]

Nonvolatile flash-memory capacitors containing graphene quantum dots (GQDs) of 6, 12, and 27 nm average sizes (d) between SiO2 layers for use as charge traps have been prepared by sequential processes: ion-beam sputtering deposition (IBSD) of 10 nm SiO2 on a p-type wafer, spin-coating of GQDs on the SiO2 layer, and IBSD of 20 nm SiO2 on the GQD layer. The presence of almost a single array of GQDs at a distance of ∼13 nm from the SiO2/Si wafer interface is confirmed by transmission electron microscopy and photoluminescence. The memory window estimated by capacitance–voltage curves is proportional to d for sweep voltages wider than ± 3 V, and for d = 27 nm the GQD memories show a maximum memory window of 8 V at a sweep voltage of ± 10 V. The program and erase speeds are largest at d = 12 and 27 nm, respectively, and the endurance and data-retention properties are the best at d = 27 nm. These memory behaviors can be attributed to combined effects of edge state and quantum confinement. [ABSTRACT FROM AUTHOR]

Radiative decay processes have been studied in graphene quantum dots (GQDs) by varying their size. The photoluminescence (PL) decay traces are well fitted to a biexponential function with lifetimes of τ1 and τ2, indicating their fast and slow components, respectively. The τ1 is almost constant, irrespective of the average GQD size (da) for two excitation wavelengths of 305 and 356 nm. In contrast, the τ2 decreases as da increases for da ≤ ∼17 nm, but da > ∼17 nm, it increases with increasing da for both the excitation wavelengths, similar to the size-dependent behaviors of the time-integrated PL peak energy. We propose that the τ1 and τ2 originate from size-independent fast band-to-band transition and size-dependent slow transition resulting from the edge-state variation at the periphery of GQDs, respectively. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) and electron-spin resonance have been used to study intrinsic defects in fused silica during ion implantation and annealing procedures designed to form and H-passivate Si crystallites. Under 250 nm (5 eV) photon excitation, the unimplanted silica has PL bands at 390 (3.2 eV) and 288 nm (4.3 eV). Implantation with 400 keV Si ions creates paramagnetic defects but reduces both the 3.2 and 4.3 eV emissions. Implantation to doses >=2x10[sup 17]Si cm[sup -2] produces an additional weak emission band at 466 nm (2.7 eV). Annealing at 1000 °C and hydrogenation at 500 °C affect both the absolute and relative intensities of the 390 and 288 nm emissions, and this is discussed with reference to known defects in the Si-crystallite/silica system. However, the emissions remain weak compared to those in unimplanted silica even though annealing removes the paramagnetic defects produced by implantation and the weak 466 nm emission observed for high doses. Since no other emission is evident at lower energies, it is concluded that implantation either alters or destroys the defect configurations responsible for the 390 and 288 nm emissions or that it creates diamagnetic defects which offer competing nonradiative relaxation channels. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: We have studied photo-induced effects of photoluminescence (PL) for dialkoxy phenylene vinylene polymer (P(MHPV)) films with different thickness under irradiation of 488nm laser line. The samples show photo-induced PL enhancement or quenching depending on excitation level, temperature, and sample thickness. Increasing behaviour of PL intensity with exposure time is observed in relatively thicker samples and the rising rate of the PL intensity is larger under higher intensity of the excitation light. The increasing behaviour of PL intensity with exposure time is changed into the decreasing one at temperatures ≤200K. It is proposed that these unusual behaviours are attributed to the chemical structural variation through degradation of the bridge double bonds linking the phenyl rings, resulting in partial disconnection of conjugation in the polymers during illumination and to the spatial diffusion of excited carriers to non-degraded P(MHPV) regions by energy transfer. [Copyright &y& Elsevier]

Abstract: ZnO films have been deposited on n-type Si (100) wafers by RF magnetron sputtering and subsequently implanted with Nb ions to fluences of (1–8)×1015 cm−2. The ultraviolet near-band-edge photoluminescence (PL) intensity of the implanted films is shown to increase with increasing fluence as well as annealing temperature and becomes maximally ∼7.5 times stronger than the emission from the un-implanted ZnO film. An increase in the PL intensity is attributed to the improved crystallinity of the ZnO resulting from a reduction in the density of native defects by the Nb implantation, as demonstrated by X-ray diffraction and X-ray photoelectron spectroscopy. [Copyright &y& Elsevier]

Abstract: Purified natural DNA extracted from Salmon sperm can only be dissolved in water; it is not soluble in any other organic solvent. Therefore, in this study, the structure of DNA was modified and its solubility was changed. The preparation of organic-soluble DNA was carried out by precipitating the purified DNA in water with the cationic surfactant cetyltrimethylammonium chloride (CTMA). The resulting DNA–lipid complex shows good solubility in alcohol, which allows the fabrication of thin films for studying the photophysical properties of DNA in a solid state. The absorption and photoluminescence (PL) behaviors of CTMA–DNA and polymethylmethacrylate (PMMA) doped with (E)-2-(2-(4-(diethylamino)styryl)-4H-pyran-4-ylidene)malononitrile (DCM) were investigated. In addition, different PL spectral behaviors with differing concentrations of DCM in two different host materials were observed. These behaviors were explained by a mechanism based on intercalation or groove binding of fluorescent dye into the base pairs or aliphatic side-chain moieties of CTMA–DNA. [Copyright &y& Elsevier]

Abstract: New dendrimers bearing a phenothiazine heterocyclic building block have been successfully prepared and their absorption and emission properties have been investigated in terms of photoluminescence (PL) and electroluminescence (EL). Particularly, the EL has been studied precisely in the heterostructural devices that are fabricated with two dendrimers. The spectrum and the intensity of EL and PL are varied with the number of generation. Significant difference of the I–V–L characteristics and the external quantum efficiency in the dendrimer devices reveals that the EL performance of the higher-generation dendrimers is higher than that of the lower-generation ones. These results suggest that the site isolation between the chromophores suppresses the non-radiative decay process and reduces the interchain molecular excimer emission from the aggregated dendrimers. [Copyright &y& Elsevier]

Abstract: Photoluminescence (PL) and electroluminescence (EL) of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and its crosslinked polymer have been investigated in this work. EL and PL of MEH-PPV were affected in both their spectral shape and intensity after introducing a small degree of crosslink between the polymer chains. It is suggested that the EL enhancement can be attributed to the chemical structural variation by the crosslink in the network structure. [Copyright &y& Elsevier]

Abstract: 300nm SiOx layers grown on p-type (100) Si wafer have been annealed to form Si nanocrystals (NCs) within SiO2. 100nm ZnO films have been then deposited on top of the SiO2:Si NC layers and annealed to form hybrid structures of ZnO/Si NCs. The PLSi (photoluminescence from Si NCs) intensity of the hybrid structures increases almost linearly with decreasing size of Si NCs (dSi) from 3.8 to 2.0nm, whilst the PLZnO (PL from ZnO) gradually increases down to dSi =~2.5nm and then sharply decreases. In the SiO2:Si NC layers without ZnO, the PLSi intensity sharply increases to a maximum at dSi =~2.5nm, and by further decrease of dSi, it decreases. These results suggest that the energy transfer from Si NCs to ZnO occurred in the range of dSi =3.8 to ~2.5nm and vice versa below dSi =~2.5nm. [Copyright &y& Elsevier]

Cathodoluminescence (CL), photoluminescence, and transmission electron microscopy have been used to study the light-emitting and structural properties of (1&1bar;02) sapphire implanted with 30-key Si ions and subsequently annealed at temperatures up to 1100°C. This procedure creates oriented Si crystallites with diameters in the range 4-5 nm together with extended defects parallel to the (0001) planes of (1&1bar;02) Al2O3. Several CL hands found in Si--implanted Al2O3(Al2O3:Si-) before and/or after annealing are compared with those from O- and Al--implanted samples. These and related experiments, including annealing temperature and implant dose dependence, suggest that a yellow CL band (2.16 eV/574 nm) from annealed Al2O3:Si- is nanocrystal related, while others are defect related. [ABSTRACT FROM AUTHOR]

Abstract: Cathodoluminescence (CL) has been studied in graphene quantum dots (GQDs) by varying their average size (d) from 5 to 35 nm. The size dependence of CL peak wavelength is very analogous to that of photoluminescence (PL) peak wavelength unusually showing non-monotonic behaviors having a maximum at d = ∼17 nm. The CL behaviors can therefore be attributed to the novel feature of GQDs, i.e., the circular-to-polygonal-shape and corresponding edge-state variations of GQDs at d = ∼17 nm as d increases. However, the peak wavelengths of CL are especially much smaller than those of PL at both ends in the size range of GQDs, possibly resulting from the recombination of the electron-beam-excited e-h pairs at higher energy states before thermalization due to fast carrier-carrier scattering dominating over electron-phonon scattering in graphene. [Copyright &y& Elsevier]