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Two-dimensional (2D) materials exhibit many unique optical and electronic properties that are highly desirable for application in optoelectronics. Here, we report the study of photodetector based on 2D Bi2O2Te grown on n-Si substrate. The 2D Bi2O2Te material was transformed from sputtered Bi2Te3 ultrathin film after rapid annealing at 400 ℃ for 10 min in air atmosphere. The photodetector was capable of detecting a broad wavelength from 210 nm to 2.4 μm with excellent responsivity of up to 3x105 and 2x104 AW-1, and detectivity of 4x1015 and 2x1014 Jones at deep ultraviolet (UV) and short-wave infrared (SWIR) under weak light illumination, respectively. The effectiveness of 2D materials in weak light detection was investigated by analysis of the photocurrent density contribution. Importantly, the facile growth process with low annealing temperature would allow direct large-scale integration of the 2D Bi2O2Te materials with complementary metal-oxide–semiconductor (CMOS) technology.

Two-dimensional (2D) materials exhibit many unique optical and electronic properties that are highly desirable for application in optoelectronics. Here, we report the study of a photodetector based on 2D Bi2O2Te grown on an n-Si substrate. The 2D Bi2O2Te material was transformed from a sputtered Bi2Te3 ultrathin film after rapid annealing at 400 °C for 10 min under an air atmosphere. The photodetector was capable of detecting a broad wavelength ranging from 210 nm to 2.4 μm with an excellent responsivity of up to 3 × 105 and 2 × 104 AW−1 and a detectivity of 4 × 1015 and 2 × 1014 Jones for deep ultraviolet (UV) and short-wave infrared (SWIR) under weak light illumination, respectively. The effectiveness of 2D materials in weak light detection was investigated by the analysis of the photocurrent density contribution. Importantly, the facile growth process at low annealing temperatures would allow the direct large-scale integration of 2D Bi2O2Te materials with the complementary metal–oxide–semiconductor (CMOS) technology.

Sulphur-doped graphene quantum dots (S-GQDs) were prepared in this work by a novel and facile method using the co-combustion (T-X-J method) of a liquid mixture of paraffin oil and carbon disulphide (CS2). Ultra-high performance (R: 307 A W−1; D*: 1.5 × 1014 Jones) ultraviolet photodetectors based on S-GQDs were fabricated under ambient conditions, shedding light on the fabrication of graphene based high-performance optoelectronic devices.

Solution processable high-performance, large-area, low-cost infrared organic photodetectors (OPDs) have been receiving more and more attention for their important applications both in scientific and technological fields. The search for a simple method to upgrade device performance for OPDs becomes increasingly important. Here, the performance of an OPD in the near-infrared (NIR) region is tremendously improved by doping iodine into the device's active layer (P3HT:PCBM:I2), 2.7 wt% iodine doping may increase the absorption by 31.3% for the active film and result in a ∼11 000-fold increase in responsivity for the detector. A high detectivity (D*) of ∼1.6 × 1012 cm Hz1/2 W−1, a good specific responsivity (R) of ∼80 A W−1 and a large EQE (external quantum efficiency) of 120% are achieved under illumination (λ = 850 nm) at room temperature. Systematic characterizations reveal that iodine-doping can introduce acceptor states in the energy band gap for the polymer layer, and thus increase the harvesting to long wavelength photons. A small dose of iodine doping can significantly induce improvement in device performance. This work demonstrates a simple but feasible method to enhance an NIR optoelectronics device.

Ultraviolet (UV) photodetectors are important optoelectronic devices. The development of a high-performance UV detector, however, has been impeded by lack of stable p-type wide gap semiconductors. Herein, an extremely high UV response for a ZnO nanorods/phenanthrene (Phen) photovoltaic detector has been realized, utilizing phenanthrene as a p-type wide gap organic semiconductor; a detectivity (D*) as high as ∼9.0 × 1013 cm Hz1/2 W−1 has been reached, showing significant potential for optoelectronic applications.

Functionalized graphene quantum dot (GQD) based materials play an important role in the development of high-performance, low-cost, large-area optoelectronic devices. The progress, however, is impeded by the poor understanding of the physical mechanism for GQDs in these devices. In this paper, chlorine doped GQD (Cl-GQD) based photovoltaic photodetectors have been fabricated using a solution process, and it was found that the presence of Cl-GQDs can significantly enhance the performance of the device. The improved performance of Cl-GQD based devices has been investigated by systematically studying the structural, morphological, optical, electrical, electrochemical and photoelectrical properties. The important photovoltaic detectors parameters such as the saturation current densities (J0), barrier heights (Φb), built-in potentials (Vbi), carrier concentrations (N) and depletion layer widths (Wd) have been calculated and discussed by studying the I–V and C–V characteristics under different illuminations. The frequency dependent capacitance and conductance have also been discussed. The results provide guidance for developing high-performance graphene based optoelectronic devices.

Visual object tracking in complex environments is a challenging task in smart surveillance fields. In order to enhance the robust tracking performance, many tracking algorithms based on multi cues integration have been proposed. However, how the multiple cues are fused during tracking is still an open issue. This paper integrates multiple cues into particle filtering framework for robust tracking in situations where no single cue is suitable. A novel quality function is introduced to evaluate the reliability of each cue. With the weights corresponding to the cue reliabilities, the combined likelihood is estimated as the weighted average of each cue. Experiments show that tracking with multiple weighted cues provides more reliable performance than single cue tracking.

Two categories of CdZnTe (CZT) wafers were grown, one by the modified vertical Bridgman method (MVBM) under Te-rich and the other under Te-stoichiometric conditions. The effects of annealing in saturated Cd vapor on CZT properties such as precipitate, infrared (IR) transmission, etch pit density (EPD) and full-width at half-maximum (FWHM) value of X-ray rocking curve were systematically discussed. As-grown CZT wafers grown under Te-rich conditions contain large-size Te precipitates with density of high-103–low-104 cm−2 and IR transmission less than 60%. The micron-size Te precipitates were entirely removed and IR transmission was increased to over 60% after annealing based on the Cd-diffusion-induced thermomigration mechanism. In comparison, as-grown wafers grown under Te-stoichiometric conditions contain Cd precipitates with density of high-105 cm−2 and IR transmission ∼60%. After annealing, the precipitate density was reduced to low-104 cm−2 and IR transmission exceeded 60%, indicating a simple and yet novel approach for eliminating Cd precipitates. The FWHM and EPD of CZT wafers were not significantly influenced by annealing. In short, crystal growth under Te-rich conditions was proved to be a practical technique for producing high-quality CZT.

Graphene quantum dots (GQDs) possess unique photoelectronic properties ascribed to quantum confinement and edge effects, which have evoked important development and wide application in the optoelectronic field. Doping GQDs with heteroatoms can further modulate the energy band structure and thus produce unexpected properties. Herein, we obtained fluorine-doped GQDs (F-GQDs) by adopting an effective preparation technique, which includes the treatment of the as-prepared reaction precursor, fluorinated carbon fibers, with ultrasonic liquid phase exfoliation. The proposed method is simple, handy, and low-cost, opening up an alternate approach to prepare F-GQDs. Through multiple characterization techniques, the effective incorporation of fluorine in GQDs was confirmed, and the as-prepared F-GQDs exhibit excellent photoelectrical properties and good ultraviolet absorption performances. Accordingly, we have fabricated a vertical photovoltaic UV detector based on F-GQDs. The unoptimized device has an exceptionally...

Graphene has attracted much attention at various research fields due to its unique optical, electronic and mechanical properties. Up to now, graphene has not been widely used in optoelectronic fields due to the lack of large-area uniform doped graphene (n-doped and p-doped) with smooth surface. Therefore, it is rather desired to develop some effective doping methods to extend graphene to optoelectronics. Here we developed a novel doping method to prepare large-area (> centimeter scale) uniform doped graphene film with a nanoscale roughness(RMS roughness ∼1.4 nm), the method (nano-metal film doping method) is simple but effective. Using this method electron doping (electron-injection) may be easily realized by the simple thermal deposition of Ag nano-film on a transferred CVD graphene. The doping effectiveness has been proved by Raman spectroscopy and spectroscopic ellipsometry. Importantly, our method sheds light on some potential applications of graphene in optoelectronic devices such as photodetectors, LEDs, phototransistors, solar cells, lasers etc.

Sulphur-doped carbon-based materials have attracted a great deal of interest because of their important applications in the fields of oxygen reduction reactions, hydrogen storage, supercapacitors, photocatalysts and lithium ion batteries. Here, we report a new member of sulphur-doped carbon-based materials, i.e. sulphur doped graphene quantum dots (S-GQDs). The S-GQDs were prepared by a hydrothermal method using fructose and sulphuric acid as source materials. Absorption and photoluminescence investigations show that inter-band crossings are responsible for the observed multiple emission peaks. The incorporation of ∼1 at% of S into the quantum dots can effectively modify the electronic structure of the S-GQDs by introducing S-related energy levels between π and π* of C. The additional energy levels in the S-GQDs lead to efficient and multiple emission peaks.

Material that can emit broad spectral wavelengths covering deep ultraviolet, visible, and near-infrared is highly desirable. It can lead to important applications such as broadband modulators, photodetectors, solar cells, bioimaging, and fiber communications. However, there is currently no material that meets such desirable requirement. Here, we report the layered structure of nitrogen-doped graphene quantum dots (N-GQDs) which possess broadband emission ranging from 300 to >1000 nm. The broadband emission is attributed to the layered structure of the N-GQDs that contains a large conjugated system and provides extensive delocalized π electrons. In addition, a broadband photodetector with responsivity as high as 325 V/W is demonstrated by coating N-GQDs onto interdigital gold electrodes. The unusual negative photocurrent is observed which is attributed to the trapping sites induced by the self-passivated surface states in the N-GQDs.

We report on a detailed investigation on the temperature-dependent behavior of photoluminescence from molecular beam epitaxy (MBE)-grown chlorine-doped ZnSe epilayers. The overwhelming neutral donor bound exciton ((ClX)-X-0) emission at 2.797 eV near the band edge with a full-width at half-maximum (FWHM) of similar to 13 meV reveals the high crystalline quality of the samples used. In our experiments, the quick quenching of the (ClX)-X-0 line above 200 K is mainly due to the presence of a nonradiative center with a thermal activation energy of similar to 90 meV, The same activation energy and similar quenching tendency of the (ClX)-X-0 line and the I-3 line at 2.713 eV indicate that they originate from the same physical mechanism. We demonstrate for the first time that the dominant decrease of the integrated intensity of the I, line is due to the thermal excitation of the "I-3 center"-bound excitons to its free exciton states, leaving the "I-3 centers" as efficient nonradiative centers. The optical performance of ZnSe materials is expected to be greatly improved if the density of the "I-3 center" can be controlled. The decrease in the luminescence intensity at moderately low temperature (30-200 K) of the (ClX)-X-0 line is due to the thermal activation of neutral-donor-bound excitons ((ClX)-X-0) to free excitons. (C) 2000 Published by Elsevier Science B.V.

It is of scientific importance to obtain graphene quantum dots (GQDs) with narrow-size distribution in order to unveil their size-dependent structural and optical properties, thereby further to explore the energy band diagram of GQDs. Here, a soft-template microwave-assisted hydrothermal method to prepare GQDs with diameters less than 5 nm ± 0.55 nm is reported. The size-dependent photoluminescence (PL) quantum yield (QY) decay lifetime and electron energy loss spectroscopy (EELS) of the GQDs are studied systematically. The QY of the GQDs with an average diameter of 2 nm is the highest (15%) among all the samples investigated and the QY decreases with increasing diameter of the GQDs. The size-dependence of the PL decay lifetime is also observed. The result suggests that spatial confinement effects related to radiative relaxation play an important role in the size-dependent decay lifetime. A realistic energy band diagram of the GQDs is deduced from the experimental results.

Ultraviolet (UV) photodetector is a kind of important optoelectronic device which can be widely used in scientific and engineering fields including astronomical research, environmental monitoring, forest-fire prevention, medical analysis, and missile approach warning etc. The development of UV detector is hindered by the acquirement of stable p-type materials, which makes it difficult to realize large array, low-power consumption UV focal plane array (FPA) detector. Here, we provide a novel structure (Al/Poly(9,9-di-n-octylfuorenyl-2,7-diyl)(PFO)/ZnO/ITO) to demonstrate the UV photovoltaic (PV) response. A rather smooth surface (RMS roughness: 0.28 nm) may be reached by solution process, which sheds light on the development of large-array, light-weight and low-cost UV FPA detectors.

Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small as 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest emission wavelength among all the solution-based QDs. The GQDs exhibit typical excitation wavelength-dependent properties as expected in carbon-based quantum dots. However, the emission wavelength is independent of the size of the GQDs. The unique optical properties of the GQDs are attributed to the self-passivated layer on the surface of the GQDs as revealed by electron energy loss spectroscopy. The photoluminescence quantum yields of the GQDs were determined to be 7–11%. The GQDs are capable of converting blue light into white light when the GQDs are coated onto a blue light emitting diode.

Graphene oxide nanosheets (GONs) have attracted considerable interest due to their potential applications in electronic and optoelectronic devices. Graphene oxide (GO) is usually prepared by using Hummers' method or modified Hummers' methods, which require graphite and strong oxidizers, followed by exfoliation to obtain GONs. The main drawbacks of this top-down approach are the use of strong oxidizing agents and small lateral size of GONs. Here, we present a self-assembly method to synthesize GONs with tunable thickness ranging from ∼1 nm (monolayer) to ∼1500 nm. The lateral sizes of the monolayer and few-layer (

In order to increase the species of organic infrared semiconductor, we synthesized organic infrared semiconductor phthalocyanine gadolinium by using o-phthalodinitrile and GdCl3 as reactants, ammonium molybdate as catalyzer. Under light and dark field modes of microscope, the translucency emerald-like powder of phthalocyanine gadolinium has been observed, the size of the small grain for the sample is around 5μm in diameter, the size of larger grain may reach to several tens of microns. The main vibrational peaks in FT-IR spectrum and Raman spectrum have been assigned. Elementary analysis shows that the experimental data of phthalocyanine gadolinium in the main agree with those of calculated data. The UV-Vis absorption spectrum of the sample indicates the sandwich-like structure of phthalocyanine gadolinium. The organic infrared semiconductor phthalocyanine gadolinium thin film on quartz substrate has been prepared with our synthesized powdered sample by using solution method. The characterizations of XRD and UV-Vis-NIR absorption have been carried out for the phthalocyanine gadolinium thin film on quartz substrate, XRD shows that phthalocyanine gadolinium diffractions occur at 2θ=6.851,8.290 and 8.820 degrees, the corresponding plane spacings (d) for the diffraction peaks are 12.8921, 10.6570, and 10.0176A.The diffraction peaks locate at low diffraction angle, suggesting that the molecular size of the phthalocyanine gadolinium is big that causes the large spacing of crystal planes. The UV-Vis-NIR absorption of phthalocyanine gadolinium thin film on quartz substrate implies that within near infrared band there is a absorption in the 1.3~2.0μm wavelength range peaked at ca. 1.75μm, indicating the important potential application value of phthalocyanine gadolinium in the field of organic infrared optoelectronics.

The study of FT-IR spectrum, Raman spectrum, UV-Vis absorption spectrum as well as photoluminescence spectrum on organic ultraviolet semiconductor KIP-OUVS-1 has been investigated. The main vibrational peaks of organic ultraviolet semiconductor KIP-OUVS-1 in FT-IR spectrum and Raman spectrum have been assigned. The study of UV-Vis solution absorption spectrum on the organic ultraviolet semiconductor KIP-OUVS-1 shows that there is an obvious ultraviolet absorption peak in 210~280nm range, there are several ultraviolet absorption peaks in 290~390nm range too. The photoluminescence spectra of organic ultraviolet semiconductor KIP-OUVS-1 at different excitation wavelengths have also been investigated, the result shows that in the excitation wavelength of 220~360nm range, the shapes for different photoluminescence peaks are similar under different excitation wavelengths, the sole difference among them is strength of the peaks. At 280nm and 300nm excitation wavelengths, the relatively strong peaks have been gotten, at 220nm and 250nm excitation wavelengths, however, the photoluminescence peaks are relatively weak. Furthermore, for organic ultraviolet semiconductor KIP-OUVS-1, the photoluminescence peaks have a stokes' red shift compared with those absorption peaks for the solution samples, and an enantiomorphous symmetry, which is the powerful experimental proof of Franck-Condon theory, between the absorption spectrum and photoluminescence spectrum has been observed too. For the reason that the organic ultraviolet semiconductor KIP-OUVS-1 may be used to prepare large-area thin film and flexible device on low-price, flexible substrates by means of thermal evaporation and solution method, thus, the authors deduce that the organic ultraviolet semiconductor KIP-OUVS-1 may have an important application potential in ultraviolet optoelectronic detecting or lighting field.

UV photodetector is a kind of important optoelectronic devices that has vital applications in both scientific and engineering fields. The development of UV photodetectors has been impeded because of lacking stable p-type wide-gap semiconductor which is crucial for high-performance, low-cost, large-array UV photovoltaic detector. In this paper, we report a novel UV photovoltaic detector fabricated using 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as a sole photoactive material. The highest detectivity (D*) reaches 9.02 × 1011 cm Hz1/2 W−1 at −1 V bias voltage at room temperature under 365 nm illumination for the un-optimized BCP based detector (without using pre-amplifier), which is the highest value for the sole UV organic photoactive material based photovoltaic detector. The optical, electrical, and photovoltaic properties, including the UV absorption, photoluminescence (PL) emission, PL excitation, I-V, C-V, and photoresponse, have been systematically investigated to disclose the internal mechan...

This letter reports the far-infrared (FIR) transmission spectra of undoped and Sb-doped p-type Hg1−xCdxTe films grown by a liquid-phase epitaxy (LPE) or molecular-beam epitaxy (MBE) technique. The activation energies of cation vacancy acceptor are found to be ∼10–12 meV and are almost independent on Cd composition. The absorption strength per Hg vacancy, useful for evaluating the cation vacancy density from the absorption spectra, is derived as 3.4×10−12 cm. Further, Zeeman splitting resulting from two different acceptors is observed from magnetotransmission measurement for the Sb-doped LPE sample, and light hole effective mass is estimated. FIR transmission seems to be a powerful tool for nondestructive characterization of impurity states in Hg1−xCdxTe.

Graphene quantum dots (GQDs) are becoming one of the hottest advanced functional materials because of the opening of the bandgap due to quantum confinement effect, which shows unique optical and electrical properties. The chlorine doped GQDs (Cl-GQDs) have been fabricated by chemical exfoliation of HCl treated carbon fibers (CFs), which were prepared from degreasing cotton through an annealing process at 1000 °C for 30 min. Raman study shows that both G and 2D peaks of GQDs may be redshifted (softened) by chlorine doping, leading to an n-type doping. The first vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbing and electron-accepting roles for (Cl)-GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ∼105 at room temperature using a 405 nm laser irradiation under the reverse bias voltage. The study expands the application of (Cl)-GQDs to the important optoelectronic detection devices.

Some newly obtained photoluminescence(PL) data from the ZnSe:Cl epilayers grown by molecular beamepitaxy(MBE) are reported here. The PL spectrum at 10K is dominated by a strong and narrow Cl°X peak at 2.797eV withthe FWHM of about 13meV. The quenching tendency of Cl°X peak with the increasing temperature is clearly characterizedby two temperature regimes, corresponding to two thermal activated nonradiative mechanisms with activation energies of about 16meV and 90meV respectively. The weak emission at 2.713eV is thermally quenched by the presence of nonradiative center with the same activation energy of about 90meV as the Cl°X. The similar quenching tendency of the2.713eV emission and the Cl°X peak implies that they are quenched by the same physical mechanisms.Keywords: MBE Growth, ZnSe:Cl Epilayer, PL 1. INTRODUCTION By virtue of the wider variation range of band-gap, Il-VI materials are suitable for various optoelectromc applicationscovering from the far-infrared to visible and even ultraviolet spectrum range. Besides, Il-VI compounds exhibit significantlylarger exciton binding energies, for example, 21meV in ZnSe' and 60meV in Zn02 compared with 4.2meV in GaAs. The

The Fourier transform and double modulation Fourier transform photoluminescence measurements were performed on HgCdTe films from liquid helium temperature to room temperature in the infrared band to 10 micrometers where the influence from room temperature background blackbody emission is very strong. From the band to band transition photoluminescence peak, which dominated in HgCdTe films with the small cadmium composition, the cadmium composition, crystal-quality-related band tail energy, and the active energy of the non-radiative Shockly-Read center, are obtained. The photoluminescence characterization method is also used to investigate the intentionally doped impurity behavior in HgCdTe. The amphoteric impurity behavior of As implanted in HgCdTe is discovered with the donor and acceptor energy level of 8.5 meV and 31.5 meV, respectively. The Ag impurity level of 70 meV in MBE HgCdTe is also found.

Multicolour emission is realized in chlorine-doped GQDs (Cl-GQDs) prepared by a facile hydrothermal method using fructose and hydrochloric acid as source materials. The average diameter of a Cl-GQD is about 5.4 nm with 2 at.% Cl. The emission colour of the Cl-GQDs can be tuned successively from blue to white, orange, green and red simply by varying the excitation wavelength between 300 and 600 nm. The multicolour emission from the Cl-GQDs can be attributed to Cl doping, which introduces additional energy levels between C π and C π*. The multicolour Cl-GQDs should find applications in bioimaging and optoelectronic devices.

The doping of carbon-based materials is of great importance due to its ability to modulate their optical, electrical and optoelectronic properties. Nitrogen-doped graphene quantum dots (N-GQDs) have received significant attention due to their superior electrocatalytic activity, optical properties and biocompatibility. The energy-level structure of N-GQDs remains unknown, which hinders the development of N-GQDs for various applications. Here, we report a one-pot synthesis method to prepare large-quantity N-GQDs at room temperature and atmospheric pressure under a prolonged reaction time. Using this approach, we can effectively dope N into the N-GQDs. As revealed by electron energy loss spectroscopy, N-doping introduces a new energy level into the electronic structure, which is responsible for tuning the optical properties of the N-GQDs.