Ex situ synthesis and optical properties of ZnO-PbS nanocomposites

Zinc oxide (ZnO) and lead sulphide (PbS) nanoparticles separately synthesized by a precipitation method were combined by an ex situ route to prepare ZnO-PbS nanocomposites with different molar ratios of ZnO and PbS. The structure and morphology of the ZnO, PbS and ZnO-PbS samples were analyzed with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A UV-vis spectrophotometer was used to collect the absorption and 325 nm He-Cd and 488 nm Ar lasers were used to collect the photoluminescence data from the samples. ZnO nanoparticles showed a broad and stable emission peak at ∼570 nm, while a strongly quantum confined emission from PbS nanoparticles was detected at ∼1344-1486 nm. The ZnO-PbS nanocomposites exhibited dual emission in the visible and near-infrared (NIR) regions that is associated with defects and recombination of excitonic centres in the ZnO and PbS nanoparticles, respectively. The PL intensity of the visible emission from the ZnO-PbS nanocomposite was shown to increase when the ZnO to PbS molar ratio was 5:1 and the emission was almost quenched at molar ratios of 1:1 and 1:5. For different molar ratios of ZnO to PbS, the PL intensity of the NIR emission from the ZnO-PbS nanocomposites was more intense than that of PbS nanoparticles.     

Excitonic photoluminescence characteristics of amorphous silicon nanoparticles embedded in silicon nitride film

We have investigated the photoluminescence (PL) properties of amorphous silicon nanoparticles (a-Si NPs) embedded in silicon nitride film (Si-in-SiN_x) grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. The PL spectrum of the film exhibits a broad band constituted of two Gaussian components. From photoluminescence excitation (PLE) measurements, it is elucidated that the two PL bands are associated with the a-Si NPs and the silicon nitride matrix surrounding a-Si NPs, respectively. The existence of Stokes shift between PL and absorption edge indicates that radiative recombination of carriers occurs in the states at the surface of the Si NPs, whereas their generation takes place in the a-Si NPs cores and the silicon nitride matrix, respectively. The visible PL of the film originates from the radiative recombination of excitons trapped in the surface states. At decreasing excitation energy (E_ex), the PL peak energy was found to be redshifted, accompanied by a narrowing of the bandwidth. These results are explained by surface exciton recombination model taking into account there existing a size distribution of a-Si NPs in the silicon nitride matrix.     

Growth and characteristics of lead sulfide nanocrystals produced by the porous alumina membrane

Lead sulfide (PbS) nanocrystals were formed by using Pb nanowires reacted with hydrogen sulfide (H₂S) gas. The structure and composition of the as-prepared nanocrystals were confirmed by scanning electron microscopy, X-ray diffraction, transmission electron microscope and energy dispersive X-ray spectroscopy. According to the differential scanning calorimeter analysis, the PbS nanocrystals in a cubic structure owned excellent thermal stability. Furthermore, the optical properties including photoluminescence (PL) and Raman scatting spectrum were also measured. The PL emission measurement of the PbS nanocrystal showed that there was an orange-red emission peak located around 655 nm. A significant quantum confinement effect made the energy gap of PbS produce a blue shift from 0.41 eV to 1.9 eV.     

Ultrasound-assisted synthesis of PbS quantum dots stabilized by 1,2-benzenedimethanethiol and attachment to single-walled carbon nanotubes

Lead sulfide (PbS) quantum dots stabilized by 1,2-benzenedimethanethiol can be synthesized by mixing Pb(NO₃)₂ and Na₂S solutions in ethanol under ultrasound irradiation. The PbS quantum dots (2.7 and 3.6 nm in diameter) are characterized by their absorption and fluorescence spectra in the near infrared region and by other surface analytical techniques. With addition of single-walled carbon nanotubes (SWNT) to the system, this ultrasound-assisted procedure allows attachment of PbS nanoparticles to SWNT surface via π–π stacking, thus providing a simple one-pot method for preparation of SWNT–PbS nanoparticle composite materials. Using the ultrasound-assisted method for synthesizing silica composites containing PbS nanoparticles by a sol–gel process is also described.     

Optical study of ZnP2 nanoparticles in zeolite Na-X

Nanoparticles of the II-V semiconductor (ZnP₂) were prepared and investigated. ZnP₂ nanoparticles were incorporated into zeolite Na-X matrix. Absorption, diffuse reflection (DR) and photoluminescence (PL) spectra of ZnP₂ nanoparticles were measured at the temperature of 77 K. Five bands B₁-B₅ are observed in both the DR and PL spectra demonstrating the blue shift from the line of free exciton in bulk crystal. We attribute the B₁-B₅ bands to five stable nanoparticles with size less than the size of zeolite Na-X supercage. We observed Stokes shift of the PL bands with respect to the absorption bands. This dependence of this Stokes shift on the particle size is nonmonotonic.     

2018年5期 电子期刊

研究了不同Mn/Pb量比的Mn掺杂CsPbCl₃（Mn：CsPbCl₃）钙钛矿量子点的发光性质。Mn/Pb的量比增加引起的Mn²⁺发光峰的红移,被认为是来源于高浓度Mn²⁺掺杂下的Mn²⁺-Mn²⁺对。进一步研究了Mn：CsPbCl₃量子点的发光效率与Mn/Pb的量比之间的关系,发现随着量比达到5：1时,其发光效率明显下降。这种发光效率下降是由于Mn掺杂浓度引起的发光猝灭。Mn：CsPbCl₃量子点的变温发光光谱证实,随着温度的升高,Mn离子发光峰蓝移,线宽加宽,但其发光强度明显增加。     

Size-dependent radiative emission of PbS quantum dots embedded in Nafion membrane

PbS quantum dots (QDs) have been incorporated in a Nafion membrane, where the QD sizes were adjusted by changing the reaction time due to the steady growing process. The radiative emissions of the samples were investigated by optical absorption, photoluminescence (PL), and time-resolved PL spectroscopy. Size-tunable emissions are shown by the PL spectrum in a range of 1.84–1.65 eV, and the emission mechanism was investigated based on a four-band envelope-function model. Possible energy transitions for the radiative emission are listed. The PL lifetime depending on the particle size is about one microsecond, and PL decay curves exhibit a trend of decreasing decay time with an increase of the PbS QD size.     

Tailoring the photoluminescence of PbS-nanoparticles layers deposited by means of the pulsed laser ablation technique

In this article, we report on the room-temperature pulsed laser deposition (PLD) of lead sulfide (PbS) nanoparticles (NPs) layers onto various substrates. It is particularly shown that the average size of PbS NPs can be controlled by varying the number of laser ablation pulses. The pulsed laser deposited PbS NPs are found to be of high-crystalline quality and their photoluminescence (PL) to blue shift significantly from 1420 to 880 nm, as their average diameter is decreased from 8.5 to 2.5 nm, thereby confirming the quantum size effect. The latitude of our PLD process is shown to permit the achievement of multilayered PbS-NPs structures of which the overall PL emission spectrum can be tailored through the appropriate stack of individual PbS-NPs layers.     

Blue–violet photoluminescence from colloidal suspension of nanocrystalline silicon in silicon oxide matrix

We report room temperature visible photoluminescence (PL), detectable by the unaided eye, from colloidal suspension of silicon nanocrystals (nc-Si) prepared by mechanical milling followed by chemical oxidation. The PL bands for samples prepared from Si wafer and Si powder peak at 3.11 and 2.93 eV respectively, under UV excitation, and exhibit a very fast (～ns) PL decay. Invasive oxidation during chemical treatment reduces the size of the nc-Si domains distributed within the amorphous SiO₂ matrix. It is proposed that defects at the interface between nc-Si and amorphous SiO₂ act as the potential emission centers. The origin of blue–violet PL is discussed in relation to the oxide related surface states, non-stoichiometric suboxides, surface species and other defect related states.     

Size regulation by bandgap-controlled etching: Application to germanium nanoparticles

A germanium (Ge) nanoparticle surface was etched in an aqueous solution under monochromatic light irradiation in the infrared-to-ultraviolet region. Since the bandgap widened up to the photon energy of the irradiating light, the average size of the nanoparticles was controlled and the size distribution narrowed. The quantum size effect explained the correlation between the resulting bandgap energy and the final size. The etched nanoparticles showed blue-green or red-infrared photoluminescence (PL) after the surfaces were terminated with organic molecules or hydrogen atoms. The PL peak energy was independent of size, indicating PL was due to radiative recombination via localized states at the Ge core surface.     

热分解含硫金属有机配合物制备近红外PbS量子点

以Pb(NO₃)₂, Na(S₂CNEt₂)·3H₂O为反应物, 在去离子水中合成含硫金属有机配合物Pb(S₂CNEt₂)₂. 氩气保护下, 在油酸和十八烯混合溶液中热分解前躯体Pb(S₂CNEt₂)₂, 反应时间分别为30, 60, 90, 120 min, 获得PbS量子点样品a, b, c, d. 通过红外光谱分析和热重-差热等手段对前躯体进行表征, 证明配体Na(S₂CNEt₂)·3H₂O中的两个硫原子与Pb²⁺配位成功. PbS量子点样品X射线衍射和透射电子显微镜分析表明, 合成的PbS为类球形纯立方晶系PbS纳米晶; 对PbS量子点样品紫外-可见吸收光谱和光致发光谱进行研究发现, 吸收光谱和光致发光谱随着反应时间的增加顺序红移, 表明优化热分解反应时间可以调控PbS量子点的吸收光谱和光致发光谱. PbS量子点样品a发射峰在1080 nm, 与硅基太阳能电池相匹配, 可作为硅基荧光太阳能聚集器的荧光材料. 关键词： 热分解法 含硫金属有机配合物 PbS量子点 反应时间     

Photoluminescence properties of powder and pulsed laser-deposited PbS nanoparticles in SiO2

Thin films of lead sulfide (PbS) nanoparticles embedded in an amorphous silica (SiO₂) host were grown on Si(1 0 0) substrates at different temperatures by the pulsed laser deposition (PLD) technique. Surface morphology and photoluminescence (PL) properties of samples were analyzed with scanning electron microscopy (SEM) and a 458 nm Ar⁺ laser, respectively. The PL data show a blue-shift from the normal emission at ∼3200 nm in PbS bulk to ∼560-700 nm in nanoparticulate PbS powders and thin films. Furthermore, the PL emission of the films was red-shifted from that of the powders at ∼560 to ∼660 nm. The blue-shifting of the emission wavelengths from 3200 to ∼560-700 nm is attributed to quantum confinement of charge carriers in the restricted volume of nanoparticles, while the red-shift between powders and thin-film PbS nanoparticles is speculated to be due to an increase in the defect concentration. The red-shift increased slightly with an increase in deposition temperature, which suggests that there has been a relative growth in particle sizes during the PLD of the films at higher temperatures. Generally, the PL emission of the powders was more intense than that of the films, although the intensity of some of the films was improved marginally by post-deposition annealing at 400 °C. This paper compares the PL properties of powder and pulsed laser-deposited thin films of PbS nanoparticles and the effects of deposition temperatures.     

Photoluminescence in amorphous TiO2-PbO systems

Photoluminescence (PL) at room temperature has been achieved in amorphous thin films and powders of the TiO₂–PbO system. They were prepared by the polymeric precursor method with [PbO]/[TiO₂] molar ratios ranging from 0.0 to 1.0. The energy position of maximum PL emission and the PL intensity showed dependence on Pb concentration. The Pb addition suggests an increase in the number of non-bridging oxygens (NBO) in the amorphous TiO₂ network. These results support the relationship between photoluminescence and structure in TiO₂-based amorphous materials. Received: 7 February 2001 / Accepted: 8 February 2001 / Published online: 27 June 2001     

Self-assembly and photoluminescence of molybdenum oxide nanoparticles

We report on the synthesis of self-assembled hillock shaped MoO₃ nanoparticles on thin films exhibiting intense photoluminescence (PL) by RF magnetron sputtering and subsequent oxidation. MoO₃ nanocrystals of size ∼29 nm are self-assembled into uniform nanoparticles with diameter ∼174 nm. The mechanism of the intense PL behaviour from MoO₃ nanoparticles is investigated and systematically discussed. The films exhibit two bands; a near-band-edge UV emission and a defect related deep level visible emission. The enhancement in PL intensity with annealing is not only by the improvement in crystallinity and grain size but also by the increase in the rms surface roughness and porosity of the films. The PL intensity is thermally activated with activation energy 1.07 and 0.87 eV respectively for the UV and visible emissions. The UV band exhibits a blue shift according to the band gap with increasing post-annealing temperatures, which suggests the possibility to tune the UV photoluminescence band by varying the oxidation temperature.     

Photoluminescence of crystalline and disordered BTO:Mn powder: Experimental and theoretical modeling

Disordered and crystalline Mn-doped BaTiO₃ (BTO:Mn) powders were synthesized by the polymeric precursor method. After heat treatment, the nature of visible photoluminescence (PL) at room temperature in amorphous BTO:Mn was discussed, considering results of experimental and theoretical studies. X-ray diffraction (XRD), PL, and UV-vis were used to characterize this material. Rietveld refinement of the BTO:Mn from XRD data was used to built two models, which represent the crystalline BTO:Mn (BTO:Mn_c) and disordered BTO:Mn (BTO:Mn_d) structures. Theses models were analyzed by the periodic ab initio quantum mechanical calculations using the CRYSTAL98 package within the framework of density functional theory at the B3LYP level. The experimental and theoretical results indicated that PL is related with the degree of disorder in the BTO:Mn powders and also suggests the presence of localized states in the disordered structure.     

Energy sublevels in an Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As quantum wire

We report the successful fabrication of a V-grooveAl_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As quantum wire system and the temperature-dependent photoluminescence (PL) measurement. The PL spectra are dominated by four features at 681, 642, 635 and 621 nm attributed to the luminescences from quantum wire, top, vertical and side-wall well regions by micro-PL measurements. By the calculations of the energy structure, discrete states (localized sublevels) in the quantum wire region and continuum states (extended along the side-wall and vertical quantum wells) in side-wall and vertical quantum wells have been obtained in both the conduction and valence bands. The calculated excitation energies explain very well the peak positions and their temperature dependence in the photoluminescence measurements.     

Effect of surface on the optical structure and thermal properties of organically capped CdS nanoparticles

Cadmium sulfide (CdS) nanoparticles were synthesized by a novel wet chemical route with various organic thiol stabilizers. Systematic experimental studies, including X-ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy, and time-resolved photoluminescence (TRPL), have evidenced that the stability, crystallinity, and optical properties of the CdS nanoparticles are affected by the organic groups which generate significant effects in surface reconstruction. Particle size was evaluated from UV–vis spectroscopy using the effective mass approximation (EMA) method and from XRD patterns based on Scherrer?s formula. The S–H vibrations are not detectable in the infrared (IR) spectra of any of the bound ligands, which are expected for thiols covalently bound to the surface of nanoparticles. PL studies reveal that the emission from the nanostructures is not much influenced by the surface states, indicating a good passivation of the particle?s surface. The time-resolved measurements reveal a biexponential decay behavior. The fast decay component is attributed to the recombination of core states, while the slow decay component of PL is associated with the charge-carrier recombination process with the involvement of surface states.     

飞秒脉冲激光辐照下硅表面光致荧光特性(英文)

采用钛宝石飞秒脉冲激光对单晶硅在空气中进行辐照,研究了硅表面在不同扫描速度和能量密度下的光致荧光特性。光致荧光谱(PL)测量表明,在样品没有退火处理的情况下,激光扫描区域观察到橙色荧光峰(603nm)和红色荧光带(680nm附近)。扫描电子显微镜(SEM)测量显示,在飞秒脉冲激光辐照硅样品的过程中硅表面沉积了大量的纳米颗粒。利用傅里叶变换红外光谱仪(FT-IR)检测到了低值氧化物SiOx(x2)的存在,并且结合能谱仪(EDS)检测结果发现氧元素在光致发光中起着重要作用。研究表明:603nm处橙色荧光峰来自微构造硅表面低值氧化物SiOx,680nm附近红色荧光带来自量子限制效应。同时样品表面硅纳米颗粒的尺寸和氧元素的浓度分别决定了红色荧光带和橙色荧光的强度,通过调节飞秒激光脉冲的扫描速度和能量密度,可以有效地控制样品的荧光强度。     

Effect of 160 MeV Ni ion irradiation on PbS quantum dots

PbS quantum dots of average size 10 nm are encapsulated in a matrix (polyvinyl alcohol (PVA)) following chemical route. They are irradiated with 160 MeV Ni¹²⁺ ion beam with fluences 10¹²-10¹³ ions/cm². Red shift in the absorption response in the optical absorption spectra reveal size enhancement of the quantum dots after irradiation and was confirmed by transmission electron microscopy (TEM). Photoluminescence (PL) study was carried out with excitation wavelength 325 nm on both unirradiated and irradiated samples at different fluences and fluence-dependent surface states and excitonic emission is observed in the PL study. The Huang-Rhys coupling constant decreases significantly after swift heavy ion (SHI) irradiation and shows a decreasing trend with increase in ion fluence.     

Multipeak-structured photoluminescence mechanisms of as-prepared and oxidized Si nanoporous pillar arrays

Silicon dominates the electronic industry, but its poor optical properties mean that it is not preferred for photonic applications. Visible photoluminescence (PL) was observed from porous Si at room temperature in 1990, but the origin of these light emissions is still not fully understood. This paper reports that an Si nanocrystal, silicon nanoporous pillar array (Si-NPA) with strong visible PL has been prepared on a Si wafer substrate by the hydrothermal etching method. After annealing in O₂ atmosphere, the hydride coverage of the Si pillar internal surface is replaced by an oxide layer, which comprises of a great quantity of Si nanocrystal (nc-Si) particles and each of them are encapsulated by an Si oxide layer. Meanwhile a transition from efficient triple-peak PL bands from blue to red before annealing to strong double-peak blue PL bands after annealing is observed. Comparison of the structural, absorption and luminescence characteristics of the as-prepared and oxidized samples provides evidence for two competitive transition processes, the band-to-band recombination of the quantum confinement effect of nc-Si and the radiative recombination of excitons from the luminescent centres located at the surface of nc-Si units or in the Si oxide layers that cover the nc-Si units because of the different oxidation degrees. The sizes of nc-Si and the quality of the Si oxide surface are two major factors affecting two competitive processes. The smaller the size of nc-Si is and the stronger the oxidation degree of Si oxide layer is, the more beneficial for the luminescent centre recombination process to surpass the quantum confinement process is. The clarification on the origin of the photons may be important for the Si nanoporous pillar array to control both the PL band positions and the relative intensities according to future device requirements and further fabrication of optoelectronic nanodevices.