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Graphene hosts intriguing photocarrier dynamics such as negative transient Terahertz (THz) photoconductivity, high electron temperature, benefiting from the unique linear Dirac dispersion. In this work, the pressure effects of photocarrier dynamics of graphene have been investigated using in situ time-resolved THz spectroscopy in combination with diamond anvil cell exceeding 9 GPa. We find that the negative THz conductivity maintains in our studied pressure range both for monolayer and bilayer graphene. In particular, the amplitude of THz photoconductivity in monolayer graphene manifests an extraordinary dropping with pressure, compared with that from the counterparts such as bulk silicon and bilayer graphene. Concomitantly, the time constant is reduced with increasing pressure, highlighting the pressure-induced hot carrier cooling. The pressure dependence of photocarrier dynamics in monolayer graphene is likely related with the enhancement of the interfacial coupling between diamond surface and sample, allowing for the activity of new electron-phonon scattering. Our work is expected to provide an impetus for the studies of high-pressure THz spectroscopy of two-dimensional materials.

Facilitating charge separation and transport of semiconductors is pivotal to improving their solar-to-hydrogen conversion efficiency. To this end, manipulating the charge dynamics via element doping has attracted much attentions. Here, we doped phosphorus (P) into two-dimensional (2D) single-crystalline quaternary sulfide (SCQS) nanobelts, enabling significantly enhanced photocatalytic H

Van der Waals heterostructures composed of different two-dimensional films offer a unique platform for engineering and promoting photoelectric performances, which highly demands the understanding of photocarrier dynamics. Herein, large-scale vertically stacked heterostructures with MoS2 and ReSe2 monolayers are fabricated. Correspondingly, the carrier dynamics have been thoroughly investigated using different ultrafast spectroscopies, including Terahertz (THz) emission spectroscopy, time-resolved THz spectroscopy (TRTS), and near-infrared optical pump-probe spectroscopy (OPPS), providing complementary dynamic information for the out-of-plane charge separation and in-plane charge transport at different stages. The initial charge transfer (CT) within the first 170 fs, generating a transient directional current, is directly demonstrated by the THz emissions. Furthermore, the TRTS explicitly unveils an intermediate free-carrier relaxation pathway, featuring a pronounced augmentation of THz photoconductivity compared to the isolated ReSe2 layer, which likely contains the evolution from immigrant hot charged free carriers to bounded interlayer excitons (∼0.7 ps) and the surface defect trapping (∼13 ps). In addition, the OPPS reveals a distinct enhancement in the saturable absorption along with long-lived dynamics (∼365 ps), which originated from the CT and interlayer exciton recombination. Our work provides comprehensive insight into the photocarrier dynamics across the charge separation and will help with the development of optoelectronic devices based on ReSe2-MoS2 heterostructures.

Understanding the coupling between electrons and phonons in iron chalcogenides FeTexSe1-x has remained a critical but arduous project in recent decades. The direct observation of the electron-phonon coupling effect through electron dynamics and vibrational properties has been lacking. Here, we report the first pressure-dependent ultrafast photocarrier dynamics and Raman scattering studies on an iron chalcogenide FeTe0.5Se0.5 to explore the interaction between electrons and phonons in this unconventional superconductor. The lifetime of the excited electrons evidently decreases as the pressure increases from 0 to 2.2 GPa, and then increases with further compression. The vibrational properties of the A1g phonon mode exhibit similar behavior, with a pronounced frequency reduction appearing at approximately 2.3 GPa. The dual evidence reveals the enhanced electron-phonon coupling strength with pressure in FeTe0.5Se0.5. Our results give an insight into the role of the electron-phonon coupling effect in iron-based superconductors.

Owing to its anisotropic optical and electrical properties, rhenium diselenide (ReSe2) has garnered considerable attention recently as a candidate material for polarization-sensitive photodetectors. However, the direct and controllable synthesis of large-sized ReSe2 with a uniform thickness is still a great challenge. Herein, we have refined the synthesis method to obtain uniform monolayer ReSe2 flakes with a size of up to ~ 106 μm on sapphire via an ambient-pressure chemical vapor deposition technique using Na promoter from sodium chloride. Interestingly, optical pump-probe spectroscopy revealed a fast switching from saturable absorption (SA) to absorption enhancement (AE) in subpicosecond time scale, followed by a slower decay induced by exciton recombination. Furthermore, both AE and SA signals exhibited clear angular dependence with a periodicity of 180°, which reflected the dichroism in nonlinear absorption dynamics. In addition, the photocarrier dynamics including free-carrier transport and subpicosecond relaxation due to exciton formation or surface trapping was probed using time resolved terahertz spectroscopy. We believe that our study serves as a reference for atomically controlled synthesis of large-sized ReSe2 and provides useful insights on its optoelectronic properties for novel device applications.

Van der Waals heterostructures composed of different two-dimensional films offer a unique platform for engineering and promoting photoelectric performances, which highly demands the understanding of photocarrier dynamics. Herein, large-scale vertically stacked heterostructures with MoS

Van der Waals heterostructures offer a new platform to engineer the properties of two-dimensional (2D) materials. Large scale heterostructures of MoS 2 and ReSe 2 monolayers were fabricated and fully investigated using time-resolved terahertz (THz) spectroscopy (TRTS), THz emission spectroscopy, and optical pump-probe spectroscopy (OPPS). The charge transfer (CT) time was estimated to be 170 fs by fitting the photocurrent model to the emitted THz pulse. In TRTS, free carrier dominated dynamic has been unambiguous investigated. In addition, it is found that interlayer and intralayer excitons are dominant in carrier dynamics before and after CT saturation in the OPPS. The intriguing results pave the way for further understanding the ultrafast carrier relaxation dynamics in 2D heterostructures and potential applications in opto-electronic devices.

Terahertz (THz) time-domain spectroscopy (THz-TDS) of polycrystalline MnCr2O4 was performed at g-factors of MnCr2O4 were also obtained using THz-TDS. This work provides new insights into the spin dynamics of chromite spinel compounds in the THz region.

The two-dimensional (2D) semiconductor lead iodide (PbI2) has recently attracted considerable attention owing to its favorable properties in both applications as photodetectors and as a precursor for lead halide perovskite solar cells. Although earlier experiments have investigated the structural stability of PbI2 below 20 GPa, the electric structures at high pressure remain ambiguous, as does the crystal structure at higher pressures. Herein, a structural phase transition and a semiconductor-metal transition are revealed in PbI2 through high-pressure femtosecond optical pump-probe spectroscopy combined with Raman spectra, synchrotron x-ray diffraction (XRD), and resistance measurements up to 70 GPa. Two discontinuities appear in the pressure-dependent amplitude of the ultrafast spectroscopy at approximately 24.8 and 37.6 GPa. Raman spectra and in situ XRD patterns confirm a structural phase transition from orthorhombic Pnma to tetragonal I4/MMM symmetry at the first discontinuity. The second discontinuity is ascribed to the closure of the bandgap and the enhanced electron-phonon interaction across the semiconductor-metal transition, which is also revealed by the temperature dependencies of resistance for PbI2 under pressure. Our results not only help to design optical devices based on lead iodide but also highlight that ultrafast spectroscopy is an efficient noncontact tool to investigate the crystalline and electric phase transition under pressures simultaneously.

We perform femtosecond pump-probe spectroscopy to in situ investigate the ultrafast photocarrier dynamics in bilayer graphene and observe an acceleration of energy relaxation under pressure. In combination with in situ Raman spectroscopy and ab initio molecular dynamics simulations, we reveal that interlayer shear and breathing modes have significant contributions to the faster hot-carrier relaxations by coupling with the in-plane vibration modes under pressure. Our work suggests that further understanding the effect of interlayer interaction on the behaviors of electrons and phonons would be critical to tailor the photocarrier dynamic properties of bilayer graphene.

The chemical nature of the organic cations governs the optoelectronic properties of two-dimensional organic-inorganic perovskites. But its mechanism is not fully understood. Here, we apply femtosecond broadband sum frequency generation vibrational spectroscopy to investigate the molecular conformation of spacer organic cations in two-dimensional organic-inorganic perovskite films and establish a correlation among the conformation of the organic cations, the charge carrier mobility, and broadband emission. Our study indicates that both the mobility and broadband emission show strong dependence on the molecular conformational order of organic cations. The gauche defect and local chain distortion of organic cations are the structural origin of the in-plane mobility reduction and broad emission in two-dimensional organic-inorganic perovskites. Both of the interlayer distance and the conformational order of the organic cations affect the out-of-plane mobility. This work provides molecular-level understanding of the conformation of organic cations in optimizing the optoelectronic properties of two-dimensional organic-inorganic perovskites., Understanding the correlation between molecular structure and properties of 2D hybrid perovskites is crucial for material design and device performance. Here, the authors reveal that conformation of organic cations in the inorganic cages has strong effects on charge mobility and broadband emission behaviour.

The frequency and time resolved conductivity in a photoexcited large-area monolayer tungsten disulfide (WS

The dynamics of carrier relaxation and charge transport of photoinduced carriers in Lead Sulfide nanocrystals with quantum confinement, synthesized by chemical bath deposition method, have been simultaneously determined using time-resolved terahertz spectroscopy with sub-picosecond time resolution. We use both Drude-Smith and Drude Lorenz model to successfully reproduce the photoconductivity spectra, which manifest that localized free-carriers not bounded excitons are responsible to the THz transport in PbS nanocrystals. The pump fluence dependence of carrier dynamics reveals the process of Auger recombination through the interaction between free carriers and excitons.

Main text The CCQM-K148.a comparison was coordinated by the BIPM on behalf of the CCQM Organic Analysis Working Group for NMIs and DIs which provide measurement services in organic analysis under the CIPM MRA. It was undertaken as a "Track A" comparison within the OAWG strategic plan. CCQM-K148.a demonstrates capabilities for assigning the mass fraction content of a solid organic compound having moderate molecular complexity, where the compound has a molar mass in the range (75 - 500) g/mol and is non-polar (pKow < −2), when present as the primary organic component in a neat organic solid and where the mass fraction content of the primary component in the material is in excess of 950 mg/g. Participants were required to report the mass fraction of Bisphenol A present in one supplied unit of the comparison material. Participants using a mass balance method for the assignment were also required to report their assignments of the impurity components present in the material. Methods used by the seventeen participating NMIs or DIs were predominantly based on either stand-alone mass balance (summation of impurities) or qNMR approaches, or the combination of data obtained using both methods. The results obtained using thermal methods based on freezing-point depression methods were also reported by a limited number of participants. There was excellent agreement between assignments obtained using all three approaches to assign the BPA content. The assignment of the values for the mass fraction content of BPA consistent with the KCRV was achieved by most of the comparison participants with an associated relative standard uncertainty in the assigned value in the range (0.1 - 0.5)%. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Vibrational properties and ultrafast photocarrier dynamics of 2H–TaS2 under pressures are studied by the experiments of Raman scattering and femtosecond time resolved spectroscopy. With increasing pressure, the linewidth of two-phonon Raman mode broadens, especially features with a sudden rapid increase above 10 GPa. Meanwhile, the ultrafast dynamics show that the fast decay through optical phonon scattering is significantly suppressed in amplitude and prolonged in lifetime; however, the weight of the slow decay component originating from acoustic phonon scattering is enhanced at high pressures. Furthermore, the electron-phonon (e-ph) coupling constant, λq, and the density of states (DOS) near the Fermi level, N(0), are evaluated qualitatively, which reveals a drastic decrease in e-ph coupling strength and a sudden increase in the DOS beyond 10 GPa. This turning pressure is consistent with the critical point where T c of superconductivity peaks while the charge density wave (CDW) vanishes, indicating the direct correlations between λq, N(0), superconductivity, and the CDW under pressure. The anomaly of the DOS may imply the occurrence of a topological transition of the electronic structure. Our work not only provides valuable information for the understanding of competition between the CDW and superconductivity in 2H–TaS2 but also may open up a routine to unveil the pressure-induced electronic topological transition.

Due to the widespread use of synthetic peptide drugs, their quantification and the analysis of impurities have become increasingly important in clinical and medical settings. Moreover, quantifying proteins using synthetic peptides as internal or external standards is a general approach, and the key to this approach is the knowing purities of the peptides. In this paper, synthetic glucagon was quantified using a mass balance method. The impurities in glucagon were analyzed and then accurately quantified separately. Karl Fischer (KF) titration and ion chromatography (IC) were used to determine the water and trifluoroacetic acid (TFA) contents in the samples, respectively. Furthermore, the inorganic ion content in the samples was determined by inductively coupled plasma mass spectrometry (ICP-MS). The sequence of peptide impurities was identified by a Thermo Fisher Orbitrap mass. Samples were determined to be 896.36 ± 0.68 mg/g after subtracting all impurity masses from the sample mass. The result can be traced to SI units.

λ-Ti3O5 was a newly discovered material with intriguing phase transition characteristics, which exhibits huge potential in the application of memory and tunable optoelectronic devices. However, the fabrication of λ-Ti3O5 still presents a great challenge and its application needs further investigation. In this work, we developed a novel method to fabricate nanocrystalline λ-Ti3O5 by carbothermal reduction of nano-TiO2, and explored its terahertz transmission properties through a temperature induced phase transition. A second phase was introduced to inhibit the grain growth of titanium oxide during the carbothermal reduction, by performing a surface modification of the precursor nano-TiO2 particles with Al2O3. This process was proved to be critical for the formation of nanocrystalline λ-Ti3O5. An in situ XRD analysis combined with a first-principles calculation based on plane wave DFT indicated that the nanocrystalline λ-Ti3O5 exhibited a semimetallic λ phase to metallic α phase transition across a large temperature range. The phase transition was accompanied by continuous, slow and reversible tuning of the terahertz transmission amplitude. This work provides considerable insights into the synthesis of λ-Ti3O5 and opens up studies on the applications of λ-Ti3O5 in the THz range, such as but not limited to sensors and smart windows.

Two-dimensional layered bi-transition metal chalcogenides with exotic physical and optoelectronic properties are becoming attractive and promising candidates for next-generation electronics and optoelectronics. Herein, we report a representative of bi-transition metal sulfide, the strip-shaped CuTaS3 crystal, analyzing its intrinsic electrical transport properties and potential optoelectronic applications by fabricating CuTaS3-based devices. The time-resolved Terahertz (THz) spectroscopy (TRTS) results indicate a rapid quenching of photoconductivity in CuTaS3 bulk within 4.1 ps photoexcitation. PL measurement and CuTaS3-based field effect transistors (FETs) show a typical n-type semiconducting behavior with a small, direct bandgap of 1.24 eV. Density functional theory (DFT) calculations reveal charge transfers between different atoms and phonon dispersion relations to help understand the structural and vibrational properties of CuTaS3. A CuTaS3-based-phototransistor was demonstrated with a responsivity of 7.6 mA W−1 and fast photoresponse time of 0.3–0.4 s, as well as excellent photoswitching stability. Our results may pave the way for developing other layered bi-transition metal chalcogenides and implementations in electronic and optoelectronic applications.

The frequency and time resolved conductivity in a photoexcited large-area monolayer tungsten disulfide (WS2) have been simultaneously determined by using time-resolved terahertz spectroscopy. We use the Drude-Smith model to successfully reproduce the transient photoconductivity spectra, which demonstrate that localized free carriers, not bounded excitons, are responsible for the THz transport. Upon the optical excitation with 400 nm and 530 nm wavelength, the relaxation dynamics of the free carriers include fast and slow decay components with time constants approximately smaller than 1 ps and between 5-7 ps, respectively. The former sub-picosecond decay is attributed to the charge carrier loss induced by the exciton formation, while both the Auger recombination and the surface trapping can contribute to the slow relaxation.

We present a systematic study on optical reflection (OR) and photoluminescence (PL) of gold nanosphere arrays formed on polystyrene (PS) templates. These optical coefficients are measured at room-temperature when the diameter of single nanosphere varies from 200 nm to 2000 nm and the shell thickness changes from 5 nm to 15 nm. The OR spectrum shows the surface plasmon resonance (SPR) and two peaks at about 375 nm and 540 nm wavelengths for all samples. The strong PL emission is observed in 315–350 nm wavelength. We find that the amplitude of the OR and PL spectra depends quite sensitively on diameter and shell thickness of the nanosphere.

A highly accurate method for measuring pentachlorophenol (PCP) concentrations in textile samples was developed. This highly accurate method for the analysis of textile samples is valuable, given the inherent challenges associated with the complexity of the sample matrix. This method can be applied to certify the concentration of pentachlorophenol in textile CRMs. A measurement procedure based on isotope dilution liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) was developed. Samples were pretreated with acid and then with n-hexane. Excellent precision was obtained. The validated concentration ranges for the method were 1.0-50 ng/g, the LOD was 1.0 ng/g, and the LOQ was 5.0 ng/g. The precision of this method is in the range of 0.80-1.40%. The method can trace to mass.

Undoped and 0.56 at.% Sb-doped ZnO thin films were prepared by pulsed laser deposition (PLD) under vacuum and an oxygen pressure of 0.2 Pa with sintered ceramic as targets. The effects of Sb doping and deposition atmosphere on structure and optical–electrical properties of the films were studied by X-ray diffraction (XRD), scanning probe microscopy (SPM), Hall Effect measurement, transmittance spectra, and photoluminescence (PL) spectra. The results showed that undoped and Sb-doped films deposited under vacuum had better crystallinity, higher carrier concentration, lower bandgap (Eg), and single violet emission as compared with the films deposited in an oxygen pressure of 0.2 Pa. Compared with undoped ZnO film, Sb-doped ZnO film had higher carrier concentration and almost uniform Eg in both atmospheres, and it exhibited obviously improved crystallinity and green emission under an oxygen pressure of 0.2 Pa. The results implied that the deposition atmosphere strongly affected the growth kinetics of the films and intrinsic defect in the films, and Sb doping seemed also to affect the growth kinetics of the films under certain conditions and introduced SbZn defects and possibly SbZn-2VZn defects, thus the structure and optical–electrical properties of the films were modified by the deposition atmosphere and Sb doping.

ZnO thin films were deposited on glass substrates at room temperature (RT) similar to 500 degrees C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 degrees C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments: the grain size increased and stress relaxed for the films deposited at 200-500 degrees C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E-g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 degrees C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.

The self-assembled growth of vertically well-aligned ZnO nanorod arrays with uniform length and diameter on Si substrate has been demonstrated via thermal evaporation and vapor-phase transport. The structural, photoluminescence (PL), and field emission properties of the as-prepared nanorod arrays were investigated. The PL spectrum at 10 K shows a strong and sharp near-band gap emission (NBE) peak ( full width at half-maximum (FWHM) = 4.7 meV) and a weak neglectable deep-level emission (DL) peak (I-NBE/I-DL= 220), which implies its good crystallinity and high optical quality. The room-temperature NBE peak was deduced to the composition of free exciton and its first-order replicas emissions by temperature-dependent PL spectra. The field emission measurements indicate that, with a vacuum gap of 400 Am, the turn-on field and threshold field is as low as 2.3 and 4.2 V/mu m. The field enhancement factor beta and vacuum gap d follows a universal equation.

C-axis-orientated ZnO thin films were prepared on glass substrates by pulsed-laser deposition (PLD) technique in an oxygen-reactive atmosphere, using a metallic Zn target. The effects of growth condition such as laser energy and substrate temperature on the structural and optical properties of ZnO films had been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission spectra and room-temperature (RT) photoluminescence (PL) measurements. The results showed that the thickness, crystallite size, and compactness of ZnO films increased with the laser energy and substrate temperature. Both the absorption edges and the UV emission peaks of the films exhibited redshift, and UV emission intensity gradually increased as the laser energy and substrate temperature increased. From these results, it was concluded that crystalline quality of ZnO films was improved with increasing laser energy and substrate temperature.

The pressure behavior of the ultraviolet (UV) and green emission bands in ZnO tetrapod-like micro-rods has been investigated at 300 and 70 K, respectively. The pressure coefficient of the UV band at 300 K is 24.5 meV/GPa, consistent with that of the band gap of bulk ZnO. However, the pressure coefficient of the green band is 25 meV/GPa, far larger than previous literature reports. The green band in this work originates from Cu-related emission, as confirmed by the fine structure observed in the spectra at 10 K. The pressure coefficients of four phonon replicas of the free exciton emission (FX) at 70 K are 21.0, 20.2, 19.8, and 19.3 meV/GPa, respectively. The energy shift rate of the FX emission and the LO phonon energies is then determined to be 21.4 and 0.55 meV/GPa. The pressure coefficient of the neutral donor bound exciton ((DX)-X-0) transition is 20.5 meV/GPa, only 4% smaller than that of FX. This confirms that the (DX)-X-0 emission corresponds to excitons bound to neutral shallow donors. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Terahertz (THz) time domain spectroscopy (THz-TDS) of a CoCr₂O₄ single crystal has been performed under magnetic fields up to 8 Tesla. The magnetic field dependences of inter-sublattice exchange resonance at different temperatures have been investigated. Benefiting from the phase and polarization sensitive detection technique in THz-TDS, the circular absorption dichroism and Faraday ellipticity in the THz frequency region are observed and are found to be tunable by the external magnetic field. The complex indices of refraction are obtained under different magnetic field, which present distinct rotatory dispersions arising from the exchange magnetic resonance.

We use ultrafast phase-contrast imaging to directly observethe cone-like terahertz (THz) Cherenkov wave generated by optical rectification of femtosecond laser pulses focused into bulk lithium niobate (LiNbO₃) single crystals. The transverse imaging geometry allows the Cherenkov angle, THz wave velocity, and optical pump pulse group velocity to be measured. Furthermore, transition-like THz radiation generated by the femtosecond laser pulse at the air-crystal boundary is observed. The effect of optical pump pulse polarization on the generation of THz Cherenkov waves and transition-like radiation in LiNbO₃ is also investigated.

Microscale wide and millimeters long comblike ZnO single crystals with well-aligned cuboid nanobranches were fabricated using a double-tube simple thermal evaporation method without the presence of...

Arrays of vertically well-aligned ZnO nanorod–nanowall junctions have been synthesized on an undoped ZnO-coated silicon substrate by a carbothermal reduction and vapour phase transport method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the nanostructures are well-oriented with the c-axis perpendicular to the substrate. The room temperature photoluminescence (PL) spectrum of the as-prepared ZnO nanostructure reveals a dominant near-band-edge (NBE) emission peak and a weak deep level (DL) emission, which demonstrates its good optical properties. Temperature-dependent PL spectra show that both the intensity of NBE and DL emissions increased with decreasing temperature. The NBE emission at 3.27 eV is identified to originate from the radiative free exciton recombination. The possible growth mechanism of ZnO nanorod–nanowall junctions is also proposed.

Vertically well-aligned ZnO nanoridge, nanorod, nanorod-nanowall junction, and nanotip arrays have been successfully synthesized on Si (100) substrates using a pulsed laser deposition prepared ZnO film as seed layer by thermal evaporation method. Experimental results illustrated that the growth of different morphologies of ZnO nanostructures was strongly dependent upon substrate temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that the ZnO nanostructures were single crystals with a wurtzite structure. Compared with those of the other nanostructures, the photoluminescence (PL) spectrum of nanorod-nanowall junctions showed the largest intensity ratio of ultraviolet (UV) to yellow-green emission and the smallest full-width at half-maximum (FWHM) of the UV peak, reflecting the high optical quality and nearly defect free of crystal structure. The vertical alignment of the nanowire array on the substrate is attributed to the epitaxial growth of the nanostructures from the ZnO buffer layer. The growth mechanism was also discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.

Zn2SiO4:Mn2+, Zn2SiO4:Eu3+ and Zn2SiO4:Mn2+ Eu3+ phosphors were prepared by a sol-gel process and their luminescence spectra were investigated. The emission bands from intra-ion transitions of Mn2+ and Eu3+ samples were studied as a function of pressure. The pressure coefficient of Mn2+ emission was found to be -25.3 +/- 0.5 and -28.5 +/- 0.9 meV/GPa for Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+ Eu3+, respectively. The Eu3+ emission shows only weak pressure dependence. The pressure dependences of the Mn2+ and Eu3+ emissions in Zn2SiO4:Mn2+ Eu3+ are slightly different from that in Zn2SiO4:Mn2+ and Zn2SiO4:Eu3+ samples, which can be attributed to the co-doping of Mn2+ and Eu3+ ions. The Mn2+ emission in the two samples, however, exhibits analogous temperature dependence and similar luminescence lifetimes, indicating no energy transfer from Mn2+ to Eu3+ occurs. (c) 2005 Elsevier B.V. All rights reserved.

Efficient green emission from ZnMgS:Mn2+ nanoparticles prepared by co-doping Mg2+ and Mn2+ ions into ZnS lattices has been observed. The synthesis is carried out in aqueous solution, followed by a post-annealing process, thus showing the features of less complexity, low cost, and easy incorporation of dopants. In comparison with the emission of ZnS:Mn2+ nanoparticles, which is located generally around 590 nm, the photoluminescence of ZnMgS:Mn2+ nanoparticles is blue-shifted by 14 nm in wavelength, leading to the enhanced green emission. The X-ray diffraction, electron spin resonance, and pressure dependent photoluminescence measurements suggest that the change of the crystal field caused by Mg2+ ionic doping and the lower symmetry in the nanoparticles may account for the blue-shift of the photoluminescence. The ZnMgS:Mn2+ nanoparticles with 1% Mn2+ doping exhibit the strongest luminescence, which could potentially meet the requirements for the construction of green light emitting diodes.

New observations on the luminescence Of In2S3 and europium-doped In2S3 nanoparticles show a green (5 10 nm) emission from In2S3 and In1.8Eu0.2S3 nanoparticles while a blue (425 nm) emission is observed from ln(1.6)Eu(0.4)S(3) nanoparticles. Both the blue and green emissions have large Stokes shifts of 62 and 110 nm, respectively. Excitation with longer-wavelength photons causes the blue emission to shift to a longer wavelength while the green emission wavelength remains unchanged. The lifetimes of both the green and blue emissions are similar to reported values for excitonic recombination. When doped with Eu3+, in addition to the broad blue and green emissions, a red emission near 615 nm attributed to Eu3+ is observed. Temperature dependences on nanoparticle thin films indicate that with increasing temperature, the green emission wavelength remains constant, however, the blue emission shifts toward longer wavelengths. Based on these observations, the blue emission is attributed to exciton recombination and the green emission to Indium interstitial defects. These nanoparticles show full-color emission with high efficiency, fast lifetime decays, and good stability; they are also relatively simple to prepare, thus making them a new type of phosphor with potential applications in lighting, flat-panel displays, and communications.

The structure and photoluminscence (PL) properties of Pr-implanted GaN thin films have been studied. RBS/channeling technique was used to explore the damage recovery at high annealing temperature and study the dependence of the radiation damage with ion implantation direction. A complete recovery of the ion implantation damage cannot be achieved at annealing temperatures up to 1050degreesC. It is found that the channeling implantation results in the decrease of the damage. The PL experimental results indicate that the PL efficiency increases exponentially with annealing temperature up to the maximum temperature of 1050degreesC. Moreover, the PL intensity is also seriously affected by ion implantation geometries. The PL intensity for the sample implanted along channeled direction is nearly 2 times more intense than that observed from the sample implanted along random direction. The thermal quenching of PL intensity from 10 to 300K for sample annealed at 1050degreesC is only 30%. (C) 2004 Elsevier B.V. All rights reserved.

The photoluminescence from ZnS1-xTex alloy with 0 < x < 0.3 was investigated under hydrostatic pressure up to 7 GPa. Two peaks were observed in the alloys with x < 0.01, which are related to excitons bound to isolated Te isoelectronic impurities (Te-1 centers) and Te pairs (Te-2 centers), respectively. Only the Te-2 related emissions were observed in the alloys with 0.01 < x < 0.03. The emissions in the alloys with 0.03 < x < 0.3 are attributed to the excitons bound to the Te-n (n greater than or equal to 3) cluster centers. The pressure coefficient of the Te-1 related peak is 89(4) meV/GPa, about 40% larger than that of the band gap of ZnS. On the other hand, the pressure coefficient of the Te-2 related emissions is only 52(4) meV/GPa, about 15% smaller than that of the ZnS band gap. A simple Koster-Slater model has been used to explain the different pressure behavior of the Te-1 and Te-2 centers. The pressure coefficient of the Te-3 centers is 62(2) meV/GPa. Then the pressure coefficients of the Te-n centers decrease rapidly with further increasing Te composition.

The need for certified reference materials (CRM) of illicit drug was emphasized by drug detection in the forensic science as a tool to improve comparability, ensuring accuracy and traceability of analytical results. The production, characterization and certification of reference materials (RMs) is a key activity in improving and maintaining a worldwide coherent system of measurements. For the first time, we developed 9 illicit drug CRMs, including methamphetamine, heroin, ketamine and others. This work describes the production of the series of illicit drug CRMs, according to ISO Guides 34 and 35, which comprises the material processing, homogeneity and stability assessment, CRMs’ characterization including moisture content, trace metal content. The certified values were assigned by two methods. Homogeneity of the CRMs was determined by an in-house validated liquid chromatographic methodology. Potential degradation during storage was also investigated and a shelf-life based on this value was established. The certified values for all the studied reference materials are traceable to the international system of units (SI). The application of purity CRMs with accurate value could eliminated the measurement error in the forensic labs, which could give the accurate and reliable results for the forensic evidence. NIM will continue to carry out in-depth cooperation with IFS with raising the level of science to provide a greater level of rigor and confidence in forensic evidence used in the Chinese criminal justice system. Ketamine and methamphetamine have been applied as CRM in the APMP comparison, and gave the good results (Lab(7)). These CRMs studied have been widely used as standards in routine inspection work for the labs affiliated Institute of Forensic Science. The application of purity CRMs with accurate value could eliminated the measurement error in the forensic labs, which could give the accurate and reliable results for the forensic evidence.

The temperature dependences of the orange and blue emissions in 10, 4.5, and 3 nm ZnS:Mn nanoparticles were investigated. The orange emission is from the T-4(1)-(6)A(1) transition of Mn2+ ions and the blue emission is related to the donor-acceptor recombination in the ZnS host. With increasing temperature, the blue emission has a red-shift. On the other hand, the peak energy of the orange emission is only weakly dependent on temperature. The luminescence intensity of the orange emission decreases rapidly from 110 to 300 K for the 10 nm sample but increases obviously for the 3 nm sample, whereas the emission intensity is nearly, independent of temperature for the 4.5 nm sample. A thermally activated carrier-transfer model has been proposed to explain the observed abnormal temperature behaviour of the orange emission in ZnS:Mn nanoparticles.