Synthesis of Multifunctional Mn‐Doped CdTe/ZnS Core/Shell Quantum Dots

The synthesis of a novel water‐soluble Mn‐doped CdTe/ZnS core‐shell quantum dots using a proposed ultrasonic assistant method and 3‐mercaptopropionic acid (MPA) as stabilizer is descried. To obtain a high luminescent intensity, post‐preparative treatments, including the pH value, reaction temperature, reflux time and atmosphere, have been investigated. For an excellent fluorescence of Mn‐doped CdTe/ZnS, the optimal conditions were pH 11, reflux temperature 100°C and reflux time 3 h under N₂ atmosphere. While for phosphorescent Mn‐doped CdTe/ZnS QDs, the synthesis at pH 11, reflux temperature 100°C and reflux time 3 h under air atmosphere gave the best strong phosphorescence. The characterizations of Mn‐doped CdTe/ZnS QDs were also identified using AFM, IR, powder XRD and thermogravimetric analysis. The data indicated that the photochemical stability and the photoluminescence of CdTe QDs are greatly enhanced by the outer inorganic ZnS shell, and the doping Mn²⁺ ions in the as‐prepared quantum dots contribute to strong luminescence. The strong luminescence of Mn‐doped CdTe/ZnS QDs reflected that Mn ions act as recombination centers for the excited electron‐hole pairs, attributing to the transition from the triplet state (⁴T₁) to the ground state (⁶A₁) of the Mn²⁺ ions. All the experiments demonstrated that the surface states played important roles in the optical properties of Mn‐doped CdTe/ZnS core‐shell quantum dots.     

Effect of CdS Interlayer on Properties of CdTe Based Quantum Dots

Highly luminescent thioglycolic acid-capped CdTe-based core/shell quantum dots (QDs) were synthesized through encapsulating CdTe QDs in various inorganic shells including CdS, ZnS and CdZnS. CdTe/CdS core/shell QDs exhibited a significant redshift of emission peaks (a maximum emission peak of 652 nm for the core/shell QDs and 575 nm for CdTe cores) with increasing shell thickness. In contrast, the redshift of photoluminescence (PL) peak wavelength of CdTe/ZnS QDs was less than 15 nm. The PL peak wavelengths of the core/shell QDs depended strongly on core size and shell thickness. The PL quantum yields (QYs) of the CdTe/CdS core/shell QDs are up to 67 % while that of CdTe/ZnS core/shell QDs is 45 %. A composite CdZnS shell made CdTe cores a high PL QY up to 51 % and broadly adjusted PL spectra (a maximum PL peak wavelength of 664 nm). The epitaxial growth of the shell was confirmed by X-ray powder diffraction analysis and luminescence decay experiments. Because of high PL QYs, tunable PL spectra, and low toxicity from a ZnS surface layer, CdTe/CdZnS core/shell QDs will be great potential for bioapplications.     

CdS/ZnS core-shell quantum dots capped with mercaptoacetic acid as fluorescent probes for Hg(II) ions

We have synthesised water soluble CdS/ZnS core-shell quantum dots (QDs) capped with mercaptoacetic acid (MAA). They were characterised by UV–vis absorption spectroscopy, fluorescence spectroscopy, FT-IR and transmission electron microscopy. Such QDs can be used as fluorescent probes for the determination of metal ions because they quench the fluorescence of the QDs. The QDs exhibit absorption and emission bands at 345?nm and 475?nm respectively, which is more longer wavelength compared to MAA-capped CdS QDs and obviously is the result of the larger particle size. The fluorescence intensity of CdS-based QDs is strongly enhanced by coating them with a shell of ZnS. In addition, such functionalised QDs are more sensitive to Hg(II) ions. Parameters such as pH, temperature and concentration of the QDs have been optimised. A high selectivity and sensitivity toward Hg(II) ions is obtained at pH 7.4 and a concentration of 12.0?mg of QDs per L. Under optimum conditions, the fluorescence intensity of CdS/ZnS QDs is linearly proportional to the concentration of Hg(II) in the range from 2.5 to 280?nM, with a detection limit of 2.2?nM. The effect of potentially interfering cations was examined and confirmed the high selectivity of this material.

Photoluminescence investigation of MPA–ZnS QDs interaction with selenite ion

The interaction between water-soluble zinc sulfide quantum dots (ZnS QDs) and selenite ion was investigated by photoluminescence method. The water-soluble ZnS QDs were synthesized using a simple and fast procedure based on the co-precipitation of nanoparticles in an aqueous solution in the presence of 3-mercaptopropionic acid (MPA), as the capping agent. Fluorescence intensity for MPA–ZnS QDs, with a strong fluorescent emission at about 430 nm, decreased in the presence of selenite. The influence of the effective parameters including pH and temperature was investigated. The results showed that under the optimum conditions, the fluorescence intensity change of QDs was linearly proportional to the selenite concentration in the range 4.0 × 10^?5–7.2 × 10^?4 mol L^?1. Moreover, the quenching mechanism was discussed to be a static quenching procedure.     

Facile synthesis of N-acetyl-L-cysteine capped ZnS quantum dots as an eco-friendly fluorescence sensor for Hg2+

This paper described an investigation of a novel eco-friendly fluorescence sensor for Hg²⁺ ions based on N-acetyl-l-cysteine (NAC)-capped ZnS quantum dots (QDs) in aqueous solution. By using safe and low-cost materials, ZnS QDs modified by NAC were easily synthesized in aqueous medium via a one-step method. The quantitative detection of Hg²⁺ ions was developed based on fluorescence quenching of ZnS QDs with high sensitivity and selectivity. Under optimal conditions, its response was linearly proportional to the concentration of Hg²⁺ ions in a range from 0 to 2.4 × 10⁻⁶ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁹ mol L⁻¹. Most of common physiologically relevant cations and anions did not interfere with the detection of Hg²⁺. The proposed method was applied to the trace determination of Hg²⁺ ions in water samples. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra.     

Enhancement of thermal conductivity and tensile strength of liquid silicone rubber by three-dimensional alumina network

ABSTRACT

Rapidly increasing demands for higher integration density and stability of electronic devices embrace higher requirements for thermally conductive silicone rubber, which is promisingly used in ultra-thin components. In this work, alumina whiskers (AWs) and alumina flakes (AFs) are used to modify liquid silicone rubber (LSR) by fabricating binary (AFs/LSR) or ternary (AWs/AFs/LSR) composites. The thermal conductivity and mechanical strength of the binary and ternary composites were investigated. Thermal conductivity of the binary AFs/LSR composite (25AFs/LSR) was 0.1990 W m^?1 K^?1, while the thermal conductivity of the ternary AFs/AWs/LSR composite (20AFs/5AWs/LSR) was 0.2655 W m^?1 K^?1. Furthermore, the tensile strength of the ternary AWs/AFs/LSR composites increased by 180.9% as compared with the binary system, increased to 7.81 MPa from 2.78 MPa due to the introduction of 1 wt% AWs. As a reason, a significant synergistic effect of AWs and AFs in the enhancement of both thermal and mechanical properties of the LSR was proved. Furthermore, the dielectric property measurements demonstrated that the ternary composites exhibited a lower dielectric constant and dielectric loss, indicating that the AWs/AFs/LSR composites were qualified to be applied in the field of electronic devices.     

Removal of Pb(II) from water samples using surface modified core/shell CdZnS/ZnS QDs as adsorbents: Characterization,adsorption, kinetic and thermodynamic studies

This research presents aqueous colloidal method to synthesize CdZnS/ZnS surface modified core/shell quantum dots (QDs) with capping agents 2-mercaptoacetic acid and 3-mercaptopropanoic acid. The QDs were characterized by the different analytical techniques. Using Plackett–Burman and Central composite designs, optimum conditions for the removal of Pb(II) from aqueous medium were developed: QDs (0.013 g) at pH 6.9, time of adsorption and desorption (20 min), temperature (61.1 °C) and dilution on 100 ppb standard solutions. Moreover, Freundlich models suggested that Pb(II) adsorption was favorable on the heterogeneous surface of QDs. The values of ΔG^° and ΔH^° (?59.26 KJ/mol.K) suggested the process was spontaneous and exothermic. The negative ΔS^° (?0.16 KJ/mol.K) indicates that the Pb(II) chemisorb on QDs. While, system follows the pseudo-second order rate equation which indicates that rate limiting step involves chemical reaction and could be influenced by the intraparticle/pore diffusion of Pb(II) ions with QDs. By using atomic absorption spectrophotometer, developed method was tested for Pb(II) removal from tap and ground water samples taken from the different districts of Karachi City. The % recovery for Pb(II) was found to be 96.4 % (tap water) and 94.8 % (ground water) with LOD = 0.1 ng mL^?1 and LOQ = 0.90 ng mL^?1.     

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1−x/ZnS (core/shell) quantum dots

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)_x(CuInS₂)_1?x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO₂ drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)_x(CuInS₂)_1?x/ZnS (core–shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose—quantum dot hybrid aerogels have apparent densities of 37.9–57.2 mg cm^?3. Their BET surface areas range from 296 to 686 m² g^?1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)₂ route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO₂ drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.     

CdSe/ZnS量子点敏化太阳能电池电子注入与光伏性能表征

合成了CdSe/ZnS核壳结构量子点(QDs), 将其作为光敏剂吸附在TiO2纳米晶薄膜上, 组装成量子点敏化太阳能电池(QDSSCs), 从电子注入速率和电池性能两方面对QDSSCs进行了表征. 为了定量研究ZnS层包覆对电子注入的影响, 运用飞秒瞬态光谱技术, 测试了包覆ZnS前后, CdSe-TiO₂体系的电子注入速率. 实验测得ZnS包覆前后电子注入速率分别为7.14×10¹¹s^-1和2.38×10^-11s^-1, 可以看出包覆后电子注入速率明显降低, 仅为包覆前的1/3. 电池器件J-V性能测试表明, ZnS作为绝缘层包覆在CdSe的表面有效提高了QDSSCs的填充因子和稳定性, 但同时也导致了效率的降低. 上述结果说明了电子注入速率的降低是导致电池电流和效率下降的重要原因, 为今后优化核壳结构QDSSCs的电流和效率提供了依据.     

Highly-controllable imprinted polymer nanoshell at the surface of silica nanoparticles based room-temperature phosphorescence probe for detection of 2,4-dichlorophenol

This paper reports a facile and general method for preparing an imprinted polymer thin shell with Mn-doped ZnS quantum dots (QDs) at the surface of silica nanoparticles by stepwise precipitation polymerization to form the highly-controllable core–shell nanoparticles (MIPs@SiO₂–ZnS:Mn QDs) and sensitively recognize the target 2,4-dichlorophenol (2,4-DCP). Acrylamide (AM) and ethyl glycol dimethacrylate (EGDMA) were used as the functional monomer and the cross-linker, respectively. The MIPs@SiO₂–ZnS:Mn QDs had a controllable shell thickness and a high density of effective recognition sites, and the thickness of uniform core–shell 2,4-DCP-imprinted nanoparticles was controlled by the total amounts of monomers. The MIPs@SiO₂–ZnS:Mn QDs with a shell thickness of 45 nm exhibited the largest quenching efficiency to 2,4-DCP by using the spectrofluorometer. After the experimental conditions were optimized, a linear relationship was obtained covering the linear range of 1.0–84 μmol L⁻¹ with a correlation coefficient of 0.9981 and the detection limit (3σ/k) was 0.15 μmol L⁻¹. The feasibility of the developed method was successfully evaluated through the determination of 2,4-DCP in real samples. This study provides a general strategy to fabricate highly-controllable core–shell imprinted polymer-contained QDs with highly selective recognition ability.     

Luminescence Enhancement based Sensing of L‐Cysteine by Doped Quantum Dots

The interaction of a presynthesized orange emitting Mn²⁺‐doped ZnS quantum dots (QDs) with L‐Cysteine (L?Cys) led to enhance emission intensity (at 596 nm) and quantum yield (QY). Importantly, the Mn²⁺‐doped ZnS QDs exhibited high sensitivity towards L?Cys, with a limit of detection of 0.4±0.02 μM (in the linear range of 3.3–13.3 μM) and high selectivity in presence of interfering amino acids and metal ions. The association constant of L?Cys was determined to be 0.36×10⁵ M^?1. The amplified passivation of the surface of Mn²⁺‐doped ZnS QDs following the incorporation and binding of L?Cys is accounted for the enhancement in their luminescence features. Moreover, the luminescence enhancement‐based detection will bring newer dimension towards sensing application.     

水热法合成AgInS2/ZnS核/壳结构量子点及其荧光性能

以硫脲为硫源,采用谷胱甘肽(GSH)和柠檬酸钠(SC)为配体,通过水热法制备了水溶性AgInS2/ZnS(AIS/ZnS)核/壳结构量子点。系统研究了反应温度和配体用量对量子点的合成及其荧光性能的影响。采用X射线衍射(XRD)、透射电子显微镜(TEM)、紫外可见吸收光谱(UV-Vis)和光致发光光谱(PL)分别对量子点的物相、形貌和光学性能进行了表征,并考察了量子点的稳定性。实验结果表明,随着反应温度从70℃升高至90℃,促进了ZnS壳层的形成,有效地钝化了量子点的表面缺陷,获得的AIS/ZnS核/壳量子点的发光强度显著提高,发光峰位从600 nm蓝移至580 nm。配体的添加可以有效地平衡Zn^2+的化学反应活性,减缓ZnS壳层的生长,抑制核壳界面缺陷的形成,还能消除量子点的表面态,当nGSH/nZn^2+=2.0,nSC/nZn^2+=2.5时,AIS/ZnS量子点的荧光性能最佳。此外,AIS/ZnS核/壳结构量子点还具有优异的光学稳定性。     

Nanoclusters formation in ion mobility spectrometry and change separation selectivity of picoline isomers

Ion mobility spectrometry (IMS) was applied to determine the influence of structural features of nanocluster formation of picoline isomers in ion mobility spectrometry. Since the results of our studies show that different isomers have the same mobilities in pure nitrogen buffer gas and their corresponding peaks are totally overlapped, 2-butanol vapor was introduced into buffer gas by means of an online system from 0 to 300 mL min^?1. We found different structural features of these isomeric compounds which cause distinct differences in ion mobility spectra. These differences result from the formation of different nanocluster product ions (~1 nm³) with different cross section areas formed depending on the occurrence of certain structural features (position of the methyl group on the pyridine ring). The size of cluster product ions formed was determined using cross section area measurements. The effects of temperature in the range from 80 to 200 °C and electric field strength have also been investigated. At 140–160 °C and 636 V cm^?1, optimum peak-to-peak resolution can be obtained.     

High Sensibility of Quantum Dots to Metal Ions Inspired by Hydroxyapatite Microbeads

An approach for the sensitive and selective determination of Ag⁺, Cu²⁺ and Hg²⁺ ions was developed based on the fluorescence quenching of mercaptopropionic acid (MPA) capped CdTe quantum dots in the existence of hydroxyapatite (HAP) nanoribbon spherulites. Among various metal ions investigated, it was found that the fluorescence of CdTe QDs was only sensitive to Ag⁺, Cu²⁺ and Hg²⁺ ions. The addition of HAP into the CdTe system could bring forward a sensitivity improvement of about 1 to 2 orders of magnitude in the detection of Ag⁺ and Cu²⁺ compared with the plain CdTe system without the existence of HAP; while there was no sensitization effect for Hg²⁺. Under optimal conditions, the detection limits for Ag⁺, Cu²⁺ and Hg²⁺ were 20, 56 and 3.0 nmol·L^?1, respectively, and the linear ranges were 0.02–50, 0.056–54 and 0.003–2.4 µmol·L^?1, respectively. Mechanisms of both QDs fluorescence quenching by metal ions and the sensitization effect by HAP were also discussed.     

Luminescence enhancement and potential application of sky-blue sulfide phosphor doped with promoter

The luminescence of the ZnS:Tm phosphor was enhanced by the addition of a KCl promoter, and a white phosphor was prepared for potential white-light applications. It was found that a high synthesis temperature and high TmF₃ concentration promoted the substitution of Tm³⁺ ions for Zn²⁺ ions. KCl doping facilitated the growth of the hexagonal phase and decreased the phase transformation temperature of ZnS. In addition, the luminescence center concentration, excitation energy absorption, effective energy transfer, charge balance, and luminescence intensity of the phosphor were improved by the addition of the KCl promoter. The emission pattern and peaks of the ZnS:Tm,KCl phosphor were similar to those of the ZnS:Tm phosphor, indicating that the ligand field variation of Tm³⁺ caused by KCl doping was small. When the sky-blue ZnS:Tm,KCl phosphor was blended with a yellow ZnS:Mn,KCl phosphor in 1:1 weight ratio, white-light emission was observed under excitation from a 6-W ultraviolet lamp (1,350 μW/cm², λ?=?254 nm). The Commission Internationale de l’Eclairage coordinates were (0.36, 0.35), and the luminance intensity was 28.1 cd/m².     

Separation and quantification of quantum dots and dissolved metal cations by size exclusion chromatography–ICP-MS

The prevalence of engineered metallic nanoparticles within electronic products has evoked a need to assess their occurrence and fate within environmental systems upon potential release of these nanoparticles. Quantum dots (QDs) are mixed-metal nanocrystals with the smallest of particle sizes (2–10 nm) that readily leach heavy metal cations in water, potentially creating a co-occurrence of nanoparticulate and dissolved metal pollutants. In this report, we develop a size exclusion chromatography–inductively coupled plasma–mass spectrometry method (SEC-ICP-MS) for the rapid separation and quantification of ~5-nm-sized CdSe/ZnS QDs and dissolved Cd²⁺ and Zn²⁺ cations in water. The SEC-ICP-MS method provided a wide chromatographic separation of CdSe/ZnS QDs and dissolved Cd²⁺ and Zn²⁺ cations only when using the smallest SEC column pore size available and an eluent composition that prevented loss of metals to column polymer surfaces by using a surfactant to ensure elution of QDs (ammonium lauryl sulfate) and a complexing ligand to ensure elution of metal cations (ethylenediaminetetraacetate). Detection limits were between 0.2 and 2 µg L^–1 for Cd²⁺ and Zn²⁺ among dissolved cation and QD phases, and ranges of linearity covered two to three orders of magnitude. Gold nanoparticles of sizes 5, 10, 20 and 50 nm were also effectively separated from dissolved Au³⁺ cations, illustrating the method applicability to a wide range of nanoparticle sizes and compositions. QD and dissolved metal concentrations measured by SEC-ICP-MS were comparable to those measured using the more conventional method of centrifuge ultrafiltration on split samples for dissolved and total metals. The applicability of the SEC-ICP-MS method to environmental systems was verified by measuring QDs and dissolved metals added to samples of natural waters. The method was also applied to monitoring CdSe/ZnS dissolution kinetics in an urban river water. The SEC-ICP-MS developed here may offer improved automation for characterising heterogeneous suspensions containing >1 µg L^–1 heavy metals.     

Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn²⁺ or Cd²⁺ is a worldwide concern. Developing an inexpensive and facile detection method for Zn²⁺ and Cd²⁺ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn²⁺ and Cd²⁺ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S²⁻). The presence of Zn²⁺ (or Cd²⁺) can “turn-on” the weak fluorescence of QDs quenched by S²⁻ due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn²⁺ (or Cd²⁺) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd²⁺). The limit of detection (LOD) for Zn²⁺ and Cd²⁺ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn²⁺ and Cd²⁺ over other metal ions and was successfully used in the detection of Zn²⁺ or Cd²⁺ in real water samples.     

Doped zinc sulfide quantum dots based phosphorescence turn-off/on probe for detecting histidine in biological fluid

We report a turn-on phosphorescence probe for detection of histidine based on Co²⁺-adsorbed N-acetyl-l-cysteine (NAC) capped Mn: ZnS quantum dots (QDs) which is directly synthesized by the hydrothermal method. The phosphorescence of NAC-Mn: ZnS QDs is effectively quenched by Co²⁺ attributing to the adsorption of Co²⁺ onto the surface of QDs with a concomitant in suppressing the recombination process of hole and electron of QDs. The phosphorescence of Co²⁺-adsorbed NAC-Mn: ZnS QDs can be recovered by binding of Co²⁺ with histidine. The quenching and regeneration of the phosphorescence of NAC-Mn: ZnS QDs have been studied in detail. The as-prepared QDs-based probe is applied to determine histidine with a linear range of 1.25–30 μM and a detection limit of 0.74 μM. The relative standard deviation for eleven repeat detections of 20 μM histidine is 0.65%. Co²⁺-adsorbed NAC-Mn: ZnS QDs show high sensitivity and good selectivity to histidine over other amino acids, metal ions and co-existing substances. The proposed QDs probe has been successfully applied to determination of histidine in human urine samples with good recoveries of 98.5–103%.     

Interfacial Electron Transfer from CdSe/ZnS Quantum Dots to TiO2 Nanoparticles: Size Dependence at the Single‐Molecule Level

Electron transfer (ET) kinetics of CdSe/ZnS core/shell quantum dots (QDs) on bare coverslips and a TiO₂ nanoparticle‐coated thin film has been investigated at the single‐molecule level. The QDs prepared have three different diameters of 3.6, 4.6, and 6.4 nm. The trajectories of fluorescence intensity are acquired with respect to the arrival time. The on‐time events and subsequent fluorescence lifetimes are shorter with decreasing size. Given the lifetime measurements for QDs on glass and TiO₂, the rate constant of ET from QDs to TiO₂ may be determined to be 1.3×10⁷, 6.0×10⁶, and 4.7×10⁶ s^?1 for the increasing sizes of the QDs. The plot of on‐time probability density versus arrival time is characterized by power‐law statistics in the short time region and a bending tail in the long time region. Marcus’s ET model is employed to satisfactorily fit the bending tail behavior and to further calculate the ET rate constants. The theoretical counterparts for the different sizes are 1.4×10⁷, 6.4×10⁶, and 1.9×10⁶ s^?1, showing good agreement with the experimental results.     

Radiation-induced conductivity in poly(phenylene vinylene) derivatives

Using the pulse-radiolysis time-resolved microwave conductivity technique the mobility and decay kinetics of radiation-induced charge carriers is studied in a series of poly(2,5-dialkoxy-phenylene vinylene) derivatives. The lower limit to the sum of the mobilities of the positive and negative charge carriers, Σμ_min, depends strongly on the alkoxy functionalization and ranges from 1.2·10⁻⁷ to 1.4·10⁻⁶ m²/V·s at room temperature. Σμ_min increases with the degree of order in the material. The after-pulse conductivity decay kinetics are disperse and are controlled by a combination of charge recombination and trapping.