Influence of pH on luminescence from water-soluble colloidal Mn-doped ZnSe quantum dots capped with different mercaptoacids

Water-soluble ZnSe/ZnS core–shell quantum dots with ZnSe core doped by manganese ions show different luminescence response to pH changes in aqueous solutions depending on the type of solubilizing agents (thioglycolic acid, mercaptoundecanoic acid, sodium mercaptopropylsulfonate). In the case of long-chain mercaptoundecanoic acid only excitonic emission is affected by pH changes. Short-chain thioglycolic acid brings about equal excitonic/Mn emission variations with pH, while mercaptopropylsulfonate-stabilized quantum dots are insensitive to pH. The mechanism discussed here is based on the competition between different relaxation channels for excited excitons in ZnSe: excitonic radiative recombination, energy transfer to Mn ion and the photogenerated electron trapping due to the presence of protonated carboxyl group. ZnSe:Mn/ZnS quantum dots stabilized with long-chain mercaptoacids may be used as a new type of fluorescence ratiometric pH-sensor or indicator.     

A Simple Strategy to Prepare Colloidal Cu‐Doped ZnSe(S) Green Emitter Nanocrystals in Aqueous Media

A novel and simple method is described for preparing colloidal Cu‐doped ZnSe(S) quantum dots (QDs) in aqueous media by introducing copper ions using the same method as to prepare colloidal ZnSe(S). More specifically, the Cu‐doped ZnSe(S) are prepared through the nucleation‐doping method in the presence of 3‐mercaptopropionic acid as stabilizers using zinc perchlorate, copper sulphate, and NaHSe as precursors. Confirmation of the preparation of Cu‐doped ZnSe(S) nanocrystals (NCs) is done with absorption and emission spectroscopies (UV–vis and PL) as the QDs show intensive green emissions. The reduction of ions Cu²⁺ to Cu⁺ is confirmed by using electron paramagnetic resonance (EPR), in which Cu⁺ ions are silent. The size determination is performed by using transmission electron microscopy (TEM) and dynamic light scattering (DLS), resulting in Cu‐doped ZnSe(S) particles with a mean diameter of 4.6 ± 3.5 nm. The excellent stability observed for the nanoparticles overcomes the intrinsic instability of traditional aqueous Cu‐doped ZnSe(S) NCs.     

Study of Polycation-Capped Mn:ZnSe Quantum Dots as a Novel Fluorescent Probe for Living Cells

Transition metal manganese ion (Mn²⁺) doped zinc selenide quantum dots (Mn:ZnSe D-Dots) have been considered as a new material for fluorescent probes in biological labeling. However, this application is limited by the low membrane permeability of D-Dots. In this work, Mn:ZnSe D-Dots were capped with the polycation Sofast to label living cells. For the first time, the efficiency of cellular uptake in living cells is significantly enhanced. Various molar ratios of Sofast to D-Dots were explored and compared to obtain the optimal reaction conditions between Sofast and D-Dots for preparing Sofast/D-Dots nano-compound. A comparison on the fluorescence labeling ability of living cells were made between Sofast/D-Dots and pure D-Dots. Results from laser scanning confocal microscope show that Sofast/D-Dots complexes enter the cells more efficiently than pure D-Dots, even with a lower concentration and shorter incubation time. The cytotoxicities of D-Dots and Sofast/D-Dots were also studied. It was found that Sofast/D-Dots have a much lower cytotoxicity than cadmium-containing quantum dots (i.e. CdTe and CdTe/ZnS). Our results suggest that the non-heavy-metal-containing Sofast/D-Dots complexes have a great potential in the application of biological labeling, especially of long-time bioimaging in living cells.     

微波法制备Mn2+掺杂ZnSe纳米材料及谱学性能研究

过渡金属掺杂的Ⅱ-Ⅳ族纳米材料有望替代CdSe类量子点作为新型的荧光标记物而受到广泛关注.利用微波加热法的体加热特点,以不同有机胺为配体溶剂,控制反应条件,制备了Mn2+掺杂的ZnSe纳米材料,并分别利用TEM、EDS、荧光光谱等手段对其形貌、结构和性能的关系进行了探索.Mn2+掺杂的纳米ZnSe粒子为200～500 nm的球形粒子,表面平整,为单晶的纤锌矿结构.掺杂后纳米粒子的发射峰显示Mn2+的跃迁发射,但不同的配体溶剂和掺杂量对产物的发光性能有明显影响.     

Determination of L-tyrosine Based on Luminescence Quenching of Mn-Doped ZnSe Quantum Dots in Enzyme Catalysis System

In this paper, we attempted to develop a novel application of Mn-doped ZnSe quantum dots (Mn: ZnSe d-dots) as probes to detect L-tyrosine (L-Tyr). The bio-conjugates of horseradish peroxidase (HRP)-conjugated Mn: ZnSe d-dots were used in the enzyme catalyzed reaction of L-Tyr with H₂O_2. Compared with traditional CdTe QDs, Mn: ZnSe d-dots have better biocompatibility and less negative impact on enzyme catalyzed system. In HRP-conjugated Mn: ZnSe-L-Tyr-H₂O₂ system, electron transfer occurred between Mn: ZnSe d-dots and HRP. It resulted in the luminescence quenching of the Mn: ZnSe d-dots., which can be used to detect L-Tyr. The coupling of efficient quenching of Mn: ZnSe d-dots photoluminescence (PL) and the effective enzyme-catalysis can afford a simple and sensitive method for L-Tyr detection. The Mn: ZnSe d-dots-enzyme catalyzed system displays great potential in the development of enzyme-based biosensing systems for various analytes.     

分子束外延生长ZnSe自组织量子点光、电行为研究

分别应用光致发光、电容电压和深能级瞬态傅里叶谱技术详细研究ZnSe自组织量子点样品的光学和电学行为.光致发光温度关系表明ZnSe量子点的光致发光热猝火过程机理.两步猝火过程的理论较好模拟和解释了相关的实验数据.电容电压测量表明样品表观载流子积累峰出现的深度(样品表面下约100nm处)大约是ZnSe量子点层的位置.深能级瞬态傅里叶谱获得的ZnSe量子点电子基态能级位置为ZnSe导带下的011eV,这与ZnSe量子点光致发光热猝火模型得到的结果一致.     

Evidence for Mn2+ fine structure in CdMnSe/ZnSe quantum dots caused by their low dimensionality

JETP Letters - The axial fine structure with strong positive zero-field splitting for Mn2+ ions in CdMnSe/ZnSe quantum dots caused by their low dimensionality was revealed. Magnetic resonance was...     

Magnetic and luminescent properties of manganese-doped ZnSe crystals

Magnetic and photoluminescent properties of manganese-doped ZnSe crystals with different impurity concentrations were investigated. The concentration of Mn²⁺ ions in ZnSe crystals has been varied from 0.01 to 0.3 at%. Magnetic and photoluminescent studies have confirmed the introduction of Mn in ZnSe crystals. It was established that Mn²⁺ ions are responsible for the emission bands with maximum at 616 nm and 633 nm, which correspond to ⁴T₂→⁶A₁ and ⁴T₁→⁶A₁ intracentre transitions of Mn²⁺ ions respectively. It was found that the concentration quenching of the photoluminescent bands is associated with Mn²⁺ ions, which are due to the formation of Mn–Mn clusters. Magnetic properties studies have shown that at high doping levels the manganese atoms form Mn–Mn clusters in ZnSe. From the temperature dependence of magnetic susceptibility of ZnSe:Mn crystals that follows the Curie–Weiss law, it was possible to estimate the Curie–Weiss temperature Θ(x) and the effective Mn–Mn antiferromagnetic exchange constant (J₁).     

水溶性CdTe:Mn量子点的双光子吸收

采用激发波长800 nm、脉宽50 fs、重复频率1 kHz的Ti:sapphire放大飞秒激光器作为激发光源,利用开孔Z扫描技术研究了不同粒径的CdTe:Mn量子点的非线性吸收性质。理论计算结果表明,同一生长时间CdTe:Mn量子点的双光子吸收系数是CdTe量子点的1.1倍,其双光子吸收系数随量子点尺寸的减小而增大,这是由于CdTe:Mn量子点非线性吸收属于反饱和吸收,掺杂了Mn元素,减小了表面缺陷浓度,表明掺杂量子点具有很好的双光子吸收现象。     

Structural, optical and Raman studies of template-free solvothermally synthesized ZnSe/ZnSe:Ce nanoparticles

The present work reports a general, single step and easy solvothermal method to synthesize well crystallized and pure phase Ce³⁺ doped ZnSe nanocrystals for the first time in a unified system. The products were well characterized by powder X-ray diffraction (XRD), UV-vis spectroscopy (UV-vis), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray diffraction (EDAX) and Raman spectroscopy. The products were found to show significant finite size effect as characterized by broadened XRD peaks, blue-shifts of the interband optical absorption edge and the asymmetric broadening of Raman spectra. The emission intensity of Ce³⁺ ion doped ZnSe was found to be considerably increased with respect to the pure one. The observed lineshape of LO modes indicates broadening that is due to the nanosized effect. The structure and properties were correlated and detailed growth mechanism is also discussed.     

基于谷胱甘肽配体的ZnSe量子点对pH响应的时间分辨荧光光谱特性

当前,有关量子点pH响应方面的研究主要集中在含Cd（镉）类量子点,且都是研究其稳态荧光光谱对pH值的响应。然而,Cd类量子点对生物体系具有一定的毒性,且稳态荧光光谱法由于受浓度等因素的影响具有一定的不稳定性,因此应用于生物体系中作为pH探针具有明显的缺点。基于以上分析,通过水相合成法,我们制备出了基于谷胱甘肽配体的水溶性ZnSe量子点,该量子点具有毒性小,生物兼容性好等特点,适合被应用于生物体系中。利用所制备的ZnSe量子点,采用时间相关单光子计数技术,结合紫外可见吸收光谱和稳态荧光光谱,对pH值在5~11不同环境下的ZnSe量子点荧光动力学进行了系统性的研究。ZnSe量子点荧光衰减具有两个寿命组分,拟合得到分别为4和24 ns。通过采集不同探测波长下ZnSe量子点荧光衰减曲线,发现其长寿命组分随探测波长的增加而增加,而短寿命组分基本不随探测波长的改变而改变,结合有关报道分析判断,短寿命和长寿命组分分别来源于核内非局域载流子复合和表面态局域载流子复合。实验发现,处于不同pH值的环境下的ZnSe量子点具有不同的荧光寿命,其荧光寿命与pH值的变化呈负相关。通过比较ZnSe量子点两种荧光寿命组分随pH值的变化关系,发现ZnSe量子点的荧光寿命对pH值的响应主要来源于长寿命组分即表面态寿命,且在不同pH值范围内响应的灵敏度不同,在6~8的pH值范围内响应最为显著,表现为长寿命组分随pH值的增加出现一个较大幅度的衰减。实验进一步发现,ZnSe量子点两个寿命组分的比值在不同pH值范围内具有较好的线性相关性,但在不同pH值范围内斜率不同,通过比较,最大值在pH值为6~8的范围内。另外,与金属钠离子相互作用实验及相关报道表明,金属离子对ZnSe量子点荧光寿命的影响较小。以上研究表明,ZnSe量子点在生物体系pH值检测中具有良好的应用前景。     

Simulation of nonlinear optical absorption in ZnSe:Co crystals

The paper presents theoretical approach to simulation of nonlinear optical absorption in zinc selenide crystals doped with cobalt (II) ions (ZnSe:Co²⁺), which was reported by us earlier (Opt. Laser Technology, V. 35, (2003), 169). We used ZnSe:Co²⁺ crystals as saturable absorbers for generation of giant-pulse eye-safe laser radiation. It was found that minimal optical losses (maximal final transmission) occurred for ZnSe samples containing 1.6×10¹⁹ cm⁻³ of Co²⁺ ions. Band structure and photoinduced molecular dynamics simulations were performed to explain the parabolic dependence of optical losses versus Co²⁺ concentration. The minimum was shown to be the result of photoinduced anharmonic electron–phonon interaction.     

Photovoltaic activity in a ZnSe/PEO–chitosan blend electrolyte junction

Thin films of ZnSe and PEO–chitosan blend polymer doped with NH₄I and iodine crystals were prepared to form the two sides of a semiconductor electrolyte junction. ZnSe was electrodeposited on indium tin oxide (ITO) conducting glass. The polymer is a blend of 50 wt% chitosan and 50 wt% polyethylene oxide. The polymer blend was complexed with ammonium iodide (NH₄I), and some iodine crystals were added to the polymer–NH₄I solution to provide the I⁻/I³⁻redox couple. The room temperature ionic conductivity of the polymer electrolyte is 4.32 × 10⁻⁶ S/cm. The polymer film was sandwiched between the ZnSe semiconductor and an ITO glass to form a ZnSe/polymer electrolyte/ITO photovoltaic cell. The open circuit voltage (V _oc) of the fabricated cells ranges between 200 to 400 mV and the short circuit current between 7 to 10 μA.     

Highly luminescent (ZnSe)ZnS core-shell quantum dots for blue to UV emission: synthesis and characterization

We synthesized nearly monodisperse bare ZnSe nanocrystallites having luminescence which ranges in wavelength from 340 to 430 nm via nucleation due to supersaturation and growth followed by size selective precipitation. Bare ZnSe dots' outermost surface is passivated with organic HDA/TOP. In order to enhance the radiative emission from the semiconductor nanocrystals, we capped the bare ZnSe quantum dots with ZnS semiconductor materials of a wider band gap and 5% of lattice mismatch and produced highly luminescent core-shell (ZnSe)ZnS quantum dots. The core-shell (ZnSe)ZnS nanocrystals show 20 times or more as greatly enhanced luminescence quantum yields as those of bare ZnSe nanocrystals. The ZnSe bare dots and the (ZnSe)ZnS core-shell dots have cubic zinc blende structures as expected from the bulk structure. The observed shapes of bare ZnSe and core-shell (ZnSe)ZnS dots are nearly spherical or ellipsoidal with the aspect ratios of 1.2 and 1.4, respectively. They are not faceted.     

Optimization of ZnSe film growth conditions for p-type doping

Wide bandgap semiconductors such as ZnSe and ZnO have attracted great interest due to their applications in solar cells, light emitting diodes, and lasers. However, these wide bandgap semiconductors are frequently difficult to be doped to heavy concentrations, greatly limiting their application. A substrate holder with a natural temperature gradient was developed for batch growth of films at different deposition temperatures, in order to investigate ZnSe film growth and doping challenges. Thin ZnSe films were grown by pulsed laser deposition and characterized using X-ray diffraction, optical transmission and reflection, Raman spectroscopy, and Energy Dispersive X-ray analysis. Deposition temperature and film stoichiometry (Zn:Se) are shown to be significant factors affecting ZnSe growth and doping. ZnSe films with improved crystallinity have been obtained by enriching with selenium and depositing at an optimized temperature. Heavily p-type ZnSe films with hole concentrations of ~2.7 × 10¹⁹ cm^?3 and resistivities of ~0.099 Ohm cm have been obtained (compared with previous reports of ~1 × 10¹⁸ cm^?3 and ~0.75 Ohm cm). The results, which are consistent with previous theoretical prediction of compensating defects in ZnSe films, can help to optimize ZnSe growth conditions and understand doping challenges in wide bandgap semiconductors.     

Ferromagnetism in Cu-doped ZnSe semiconducting quantum dots

The projection of integrating optical, magnetic and electronic functionalities into a single material have aggravated passionate attention in mounting wide band gap diluted magnetic semiconductor (DMS) in the midst of room temperature ferromagnetism. We report the evidence of ferromagnetism in Cu-doped ZnSe quantum dots (QDs) below room temperature, grown from a single source precursor by lyothermal method with the sizes of approximately 3.2–5.14 nm. QDs mainly exhibit paramagnetic behavior between 80 and 300 K, with a weak ferromagnetic/anti-ferromagnetic exchange at lower temperature as observed by superconducting quantum interference device (SQUID) magnetometer. From the Curie–Weiss behavior of the susceptibility, Curie temperature (T _c) of Cu-doped ZnSe sample has been evaluated. From EPR, we obtain the Lande-g factor in the Zeeman interaction term as 2.060. Photoluminescence and EPR measurements support and confirm the view that Cu²⁺ substitutes for Zn²⁺ in Cu-doped ZnSe quantum dots.     

Nonlinear transmittance of ZnSe:Fe<Superscript>2+</Superscript> crystal at a wavelength of 2.92 μm

ZnSe crystals doped with Fe²⁺ ions are produced with the diffusion method under the conditions for thermodynamic equilibrium of solid ZnSe, solid Fe, and vapors (S_ZnSe-S_Fe-V). The transmittance of the samples is varied from 7 to 50% (in the absence of the antireflection coating) for a wavelength of about 3 μm. It is demonstrated that the transmittance of the ZnSe:Fe²⁺ crystals increases with an increase in the energy density of the high-power laser radiation with a wavelength of 2.92 μm. An equation that describes the propagation of the resonant radiation in a medium with saturable absorption at an arbitrary ratio of the radiation pulse duration to the relaxation time of the medium is introduced for the analysis of the experimental dependence of the transmittance on the energy density.     

New method to induce 2D–3D transition of strained CdSe/ZnSe layers

We present new growth conditions for growing high-quality CdSe/ZnSe quantum dots with photoluminescence emission measurable up to room temperature. The surface morphology is characterized in situ by Reflective High Energy Electron Diffraction (RHEED). The key point is the introduction of a new step in the growth process using amorphous selenium to induce a 2D–3D transition of a CdSe strained layer on ZnSe to form the dots. Optical characterizations by photoluminescence of CdSe/ZnSe quantum dots obtained that way, as well as X-ray diffraction results are also discussed here.     

近红外量子点的发光机理研究

近红外量子点具有独特的光学性质,如荧光量子产率高,荧光寿命长,荧光发射波长可调,半峰宽窄且斯托克斯位移较大,耐光漂白能力强等, 及“近红外生物窗口”的优势,使它们在生物荧光标记、太阳能电池、量子化计算、光催化、化学分析、食品检测及活体成像等领域具有巨大的潜在应用价值。目前对近红外量子点的发光机理研究还不够完善,针对国内外的研究现状,重点对核/壳结构的量子点(CdTe/CdSe,CdSe/CdTe/ZnSe等)、三元量子点(Cu-In-Se,CuInS₂等)和掺杂型量子点(Cu∶InP等)三种不同类型近红外量子点的发光机理进行了综述。其中,Type-Ⅱ型核/壳结构量子点的发光机理多为带间复合发光,三元量子点以本征缺陷型发光为主,掺杂型量子点多为杂质缺陷型发光。探讨了近红外量子点发光原理存在的问题及发展的方向。对近红外量子点的发光机理进行系统地研究不仅有助于我们理解近红外量子点的发光性质,而且对完善相似高品质量子点的合成方法具有重要意义。