Synthesis and characterization of ZnS:Mn2+ nano-particles for white-light emitting

The sol-gel method was used to obtain a kind of white-light emitting ZnS:Mn2+ nanoparticles capped by methacrylic acid with an average particle size of approximately 7 nm. The photoluminescence spectra, X-ray diffraction spectra, Fourier transform infrared reflection spectra and ultraviolet absorption spectra were used to measure their optical properties and crystal structures. The ZnS:Mn2+ nanoparticles with 0.58 wt% Mn2+ concentration emitted white light when excited by 380 nm. The PL spectrum exhibits two emission peaks under irradiation: one at 480 nm generated from the ZnS matrix, and one at 590 nm emitted by the doped Mn2+ ions. The nanoparticles will only emit white light with the optimum Mn2+ concentration (0.58 wt%). X-ray diffraction demonstrates the synthesized ZnS:Mn2+ nanoparticles have zinc blend crystal structure, and the infrared patterns of the capped ZnS:Mn2+ nanoparticles and methacrylic acid are comparable, indicating that the methacrylic polymer has capped or modified ZnS:Mn2+ nanoparticles.     

Paramagnetic nature of Mn doped ZnS nano particles in opto electronic device application

Manganese (Mn²⁺) doped ZnS nano sized powder was prepared by co precipitation method with different concentration from 1 to 5 %. The X-ray diffraction pattern indicates that the prepared powders are in cubic structure with the crystallite sizes lie in the range of 10–12 nm. Diffuse reflectance studies enlightens that an increment in the band gap (3.38–3.55 eV) with increasing dopant. The morphology and size of the sample could be intuitively determined by field emission scanning electron microscope and it shows that ZnS and Mn doped ZnS nanoparticles are appeared as spherical shape. The replacement of Zn by Mn is confirmed by energy dispersive analysis. TEM images confirm the spherical shape of the nanoparticles and SAED images exhibit the crystalline nature and confirm the cubic nature of the synthesized samples. The prepared luminescent nanoparticles of Mn doped ZnS have emission peak at around 617 nm. The symmetry and electronic structure of the Mn doped samples are studied with electron paramagnetic resonance.The paramagnetic nature of Mn doped ZnS nano particles are validated by using vibrating sample magnetometer spectra at room temperature. Thermal analysis measurement of the samples shows that the thermal stability of Mn doped ZnS is higher than the undoped ZnS. This corroborates that ZnS:Mn doping is attributed to the removal of water and it enhanced the crystallinity.     

Synthesis and optoelectrochemical properties of ZnS:Mn nanocrystals

Mn2+ ions doped ZnS semiconductor nanocrystals (ZnS:Mn NCs) were synthesized using colloidal chemical method at 70 degrees C without any capping agents. The as-prepared undoped ZnS and ZnS:Mn NCs were characterized by UV-Vis absorption spectra, fluorescent emission spectra, X-ray powder diffraction (XRD), inductively coupled plasma analysis (ICP), X-ray photoelectron spectroscopy (XPS), Dynamic light scattering (DLS), cyclic voltammogram and electronic transmission microscopy (TEM). The dependence of photoluminescence of ZnS:Mn NCs on dopant concentration was studied. The results show that Mn2+ ions mainly stay at ZnS nanocystal surface, and Mn2+-surface defect state complex was formed, as a result of which, surface defect emission of ZnS nanocrystals was substituted with Mn2+-related PL emission. The strongest fluorescent emission intensity was obtain at 1.85 at% Mn2+ doped ZnS:Mn NCs. The Mn2+ doped ZnS:Mn NCs are of 5 nm in diameter. The emission peak at 575 nm is attributed to d-d (4T1 --> 6A1) transition of Mn2+ ions. The existence of Mn2+-related photoluminescence could be well correlated with cyclic voltammogram of Mn2+-doped NCs, where pair of oxidation and reduction peaks were clearly observed due to the doped Mn2+ ions. The adsorbed Mn2+ ions on ZnS NCs produced neither Mn2+ emission nor redox peaks. For heavily doped ZnS:Mn NCs (4.87 at%), redox peaks gap in cyclic voltammogram became larger and new oxidation peak appeared. Correspondingly, when the Mn2+ doping concentration reached 4.87 at%, the Mn2+-related emission totally disappears due to the Mn-Mn interactions. This work implys that electrochemical technique is possibly an useful tool to probe the local structure of doped Mn2+ ions.     

基于ZnS纳米材料的生物分子检测

利用三种发光波长的ZnS基纳米材料（ZnS、ZnS：Cu和ZnS：Mn）作为荧光标记物进行人免疫球蛋白（IgG）分子的免疫检测,X射线衍射（XRD）表明,过渡金属离子掺杂会导致ZnS纳米晶的结晶化尺寸减小;荧光光谱显示,ZnS、ZnS：Cu和ZnS：Mn纳米材料的发光波长分别为430nm、560nm和590nm。利用羊抗人IgG作为捕获抗体,分别制备免疫检测金基底和ZnS基荧光探针,分别进行空白实验、加入待测物人IgG实验,表明具有很好的检测选择性。     

Possible weak ferromagnetism in pure and M (Mn, Cu, Co, Fe and Tb) doped NiGa2O4 nanoparticles

We report on the structural and magnetic properties of nanoparticles of NiGa2O4 and 5 at.% M doped (M = Mn2+, Cu2+, Co2+, Fe3+ and Tb3+) at Ga site of NiGa2O4, synthesized by gel-combustion method. The particle size, as investigated by X-ray diffraction and transmission electron microscopy, could be fine tuned by a controlled annealing process. Weak ferromagnetism becomes significant, when the particles are in the nano regime (5-7 nm). The magnetization becomes insignificant at larger particle size ( 150 nm). Cu2+ and Tb3+ doped NiGa2O4 nanoparticles showed relatively large room temperature ferromagnetism compared to other doped (Fe, Mn and Co) and undoped NiGa2O4 samples. The weak ferromagnetism observed in the nanoparticles of NiGa2O4, which is antiferromagnetic in the bulk, is due to the surface disordered states with uncompensated spins.     

Fabrication of ZnS nanoparticles and nanorods with cubic and hexagonal crystal structures: a simple solvothermal approach

ZnS nanoparticles and nanorods with control over their crystal structure are fabricated through a solvothermal approach by changing the solvent used for the synthesis. The synthetic approach is suitable to fabricate ZnS nanoparticles with various sizes by varying the synthesis temperatures. Quantum confinement phenomena are studied by tailoring the particle sizes for both wurtzite and sphalerite polymorphs of ZnS. Photoluminescence studies reveal that the surface states greatly influence the emissions from the nanostructures. Wurtzite nanoparticles exhibit band-edge related UV emission owing to the effective surface passivation by the ethylene glycol molecules used as the solvent for the synthesis. On the other hand, the photoluminescence spectra of the cubic nanoparticles are mainly dominated by their surface states. Some of the nanorod samples exhibited Zn-vacancy related green emissions along with the surface defect related blue emission band. It is also demonstrated that ZnS nanostructures could be easily doped with useful impurities via this synthesis approach to tailor their luminescent properties.     

Photoluminescence decay kinetics of doped ZnS nanophosphors

Doped nanophosphor samples of ZnS:Mn, ZnS:Mn, Co and ZnS:Mn, Fe were prepared using a chemical precipitation method. Photoluminescence (PL) spectra were obtained and lifetime studies of the nanophosphors were carried out at room temperature. To the best of our knowledge, there are very few reports on the photoluminescence investigations of Co-doped or Fe-doped ZnS:Mn nanoparticles in the literature. Furthermore, there is no report on luminescence lifetime shortening of ZnS:Mn nanoparticles doped with Co or Fe impurity. Experimental results showed that there is considerable change in the photoluminescence spectra of ZnS:Mn nanoparticles doped with X (X = Co, Fe). The PL spectra of the ZnS:Mn, Co nanoparticle sample show three peaks at 410, 432 and 594?nm, while in the case of the ZnS:Mn, Fe nanoparticle sample the peaks are considerably different. The lifetimes are found to be in microsecond time domain for 594?nm emission, while nanosecond order lifetimes are obtained for 432 and 411?nm emission in ZnS:Mn, X nanophosphor samples. These lifetimes suggest a new additional decay channel of the carrier in the host material.     

Fabrication and luminescence of ZnS:Mn2+ nanoflowers

Visually striking nanoflowers composed of ZnS:Mn2+ nanoparticles are prepared and characterized. The configurations of these fractal structures are very sensitive to both the pH values of the particle solutions from which they are precipitated and the substrates on which they are deposited. At pH 2.2, the fractal structures resemble trees without leaves; at pH 7.7, they are tree-like with four arms and at pH 11.0 they resemble trees with six arms. High resolution transmission microscopy reveals that the nanoflowers are composed of ZnS:Mn2+ nanoparticles of 2-5 nm in size. X-ray photoelectron spectral data indicate that the sample compositions of nitrogen, chlorine, and sulfur vary gradually with pH values of the solutions. These changes may have an impact on both the fractal configuration and the luminescence properties. The emission spectra of the particle solutions at pH values of 2.2 and 11.0 are similar with the emission maximum at 475 nm. As the pH value approaches 7.7, the emission spectral maximum shifts to longer wavelengths. At a pH value of 7.7, the emission peak wavelength is the reddest, 520 nm. The emission peak of the nanoflowers at a pH value of 9.3 is 510 nm, while the emission spectrum of the nanoflowers at 5.2 has two peaks at 500 nm and 440 nm, respectively. These blue-green emissions are attributed to defects and are the dominant luminescence from the nanoflowers. The emission from Mn2+ dopant is only observed in the delayed spectra of the fractal solid samples.     

Synthesis and characterization of sol-gel derived ZnS : Mn2+ nanocrystallites embedded in a silica matrix

Synthesis and characterization of undoped and Mn²⁺ doped ZnS nanocrystallites (radius 2–3 nm) embedded in a partially densified silica gel matrix are presented. Optical transmittance, photoluminescence (PL), ellipsometric and electron spin resonance measurements revealed manifestation of quantum size effect. PL spectra recorded at room temperature revealed broad blue emission signal centred at ∼ 420 nm and Mn²⁺ related yellow-orange band centred at ∼ 590 nm while ESR indicated that Mn in ZnS was present as dispersed impurity rather than Mn cluster.     

Luminescent properties of ZnS:Mn2+/ZnS core/shell nanocrystals

High-quality ZnS:Mn2+/ZnS core/shell nanocrystals (NCs) with a core crystal diameter of 6.1 nm and 1.15 nm thick shells were synthesized via a high-boiling solvent process. The energy levels of the conduction band and valance band are estimated to be -3.2 eV and -6.8 eV by cyclic voltammetry and ultraviolet-visible (UV-vis) absorption spectra. The ZnS:Mn2+/ZnS NC emission peak is primarily located at 580 nm under 310 nm light excitation, originating from the charge transition from 4T1 to 6A1 within the 3d5 configuration of the Mn2+ ion. Based on ZnS:Mn2+/ZnS NCs as the active layer electroluminescent devices, the emission peak mainly locates at 460 nm with one shoulder emission peaking at 580 nm. The photoluminescence and electroluminescence properties of ZnS:Mn2+/ZnS NCs are investigated in the view of charge carrier injection and energy level alignment.     

Nanocrystal formation and luminescence properties of ZnS based doped nanophosphors

There is an ongoing interest on the photoluminescence (PL) and related properties of doped nano ZnS since there is a large change in their PL properties with particle size reduction. Such PL properties are theoretically predicted to be much enhanced with ZnS particle sizes below the Bohr radius, i.e., in ZnS for particle sizes less than 5 nm or so. We start this discussion by first suggesting some nanoparticle formation mechanisms. The type of capping mechanism used dictates the temporal PL stability under different ambient conditions and other post-processing device requirements. We then describe results on PL of our different doped nanocrystalline ZnS and compare our interpretation of results with those available in literature. We have used 3-D plots featuring the effect of different excitation wavelengths on the PL emission profile and its intensity variation on nanocrystalline ZnS doped with different ions. Reported results and our own data suggests that the nanoparticle formation leads to drastic change in PL emission peaks-such that they are often greatly different from those of similar bulk samples. These features are seen in cases where PL is due to electron recombination from dopant and codopant sites, e.g., during Cu and Ag doping. Such results are explained due to greatly modified band structure with nanoparticle formation and bandgap enhancement where dopant and codopant levels have also greatly changed. However, in nanocrystalline samples where the PL mechanism is due to intraion transitions of dopants (e.g., in Mn doping), the luminescence properties remain similar to those of the bulk--this is because as long as the host material and its related crystal field is the same, such electron transition levels remain similar.     

Luminescence properties of ZnS:Mn nanocrystals embedded in SiO2 by ion implantation

Sequential multi-energy implantations of zinc and sulphur ions have been performed in a 250-nm thick SiO₂ layer thermally grown on 1 1 1 silicon. Energies and doses have been chosen to produce 10 at.% constant concentration profiles overlapping over about 100 nm. Manganese is subsequently introduced at various levels by the same way. Thermal treatments (from 700 to 1100 °C) lead to the formation of nanometric precipitates of the luminescent compound ZnS:Mn. A bimodal size distribution is observed, with a quasi-single layer of large particles (40 nm) in the end-of-range region and much smaller precipitates between this layer and the surface. The orange emission is maximal when the Mn concentration is close to 3%. Several hours at 900 °C is the best thermal budget for maximal luminescence intensity at room temperature. A shift of the excitation spectrum related to size variations, shows that the particles of smaller size are mainly responsible for the observed luminescence. In agreement with other authors, the luminescence lifetime is found in the ms range and increases with the nanocrystal diameter, tending to the lifetime of bulk ZnS. The luminescence of ZnS:Mn nanoparticles embedded in SiO₂ by ion implantation is also shown to be very stable during long UV light irradiation.     

Localization of Mn2+ ions in mesoporous NnS

Nanocrystalline cubic ZnS doped with 0.2% mol manganese, exhibiting a stable mesoporous structure, was synthesized at room temperature by a non toxic surfactant-assisted liquid-liquid reaction. The X-ray diffraction measurements demonstrate the formation of a sponge-like mesoporous material built from cubic ZnS nanocrystals of 1.8 nm average sizes, with a tight distribution of pores of 1.8 nm mean diameter. The transmission electron microscopy images confirm the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from cubic ZnS nanocrystallites of 2.1 nm average size. The resulting tight distribution of crystallites and pores yields a well resolved Electron Paramagnetic Resonance spectrum, with the narrowest reported component lines attributed to three types of isolated Mn2+ centers, called Mn2+(I), Mn2+(II) and Mn2+(III). From the analysis of the spin Hamiltonian parameters it is shown that in the Mn2+(I) centers the paramagnetic ion is situated at substitutional Zn sites in the ZnS nanocrystals, being also subjected to a small axial distortion. The relative concentration changes under thermal treatment experiments strongly suggest that in both Mn2+(II) and Mn2+(III) centers the Mn2+ ion is localized on the surface of the ZnS nanocrystallites, being bond to an oxygen ion in the first case and to an additional water molecule in the second case.     

Local structure at Mn2+ ions in vacuum annealed small cubic ZnS nanocrystals self-assembled into a mesoporous structure

A mesoporous structure of self-assembled nanocrystals of cubic ZnS doped with Mn2+ ions with a homogeneous distribution of pores of similar size was synthesized at room temperature by a surfactant-assisted liquid-liquid reaction. The component nanocrystals exhibit a high crystallinity and a tight size distribution centered at 2 nm, as well as the narrowest Electron Paramagnetic Resonance (EPR) spectra linewidth and the best resolution reported so-far, effects attributed to self-assembling. The observed EPR spectra consist of lines from the substitutional Mn2+(I) and surface Mn2+(II) and Mn2+(III) centers. Here we show that, in contrast with previous reports, our EPR spectra are highly sensitive to structural changes during pulse annealing in vacuum up to 500 degrees C. The changes are related to the transformation of the surface Mn2+ centers in new Mn2+ centers, attributed to an oxidation process in which the thermal decomposition of the Tween 20 additive, also observed by EPR, seems to be involved. We have also been able to observe, for the first time by EPR spectroscopy, the formation of the ZnO phase and the nanocrystals size increase, which occur during annealing up to 500 degrees C, structural changes confirmed by XRD and TEM observations on the samples previously investigated by EPR.     

Triboluminescent properties of zinc sulfide phosphors due to hypervelocity impact

The emission of light due to crystal fracture, or triboluminescence (TL), is a phenomenon that has been known for centuries. One of the most common examples of TL is the flash created from chewing Wint-O-Green Lifesavers^®. From 2004 to 2006, research was completed using the two-stage light gas gun located at the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama to measure the TL properties for zinc sulfide doped with both manganese (ZnS:Mn) and copper (ZnS:Cu). Results clearly show that hypervelocity impact-induced TL has been observed for both ZnS:Mn and ZnS:Cu. For ZnS:Mn, TL produced during 4.7 and 5.7 km/s impacts was statistically more luminous than was observed from similar data collected at 3.3 km/s. The TL decay time for ZnS:Mn was found to be 292 ± 58 μs, which is totally consistent with earlier measurements that did not use impact as an excitation source. Further, the emission of TL from ZnS:Mn undergoing hypervelocity impact has been demonstrated to have a significant component at the known peak emission wavelength of ZnS:Mn of 585 nm. Small TL emission generated as a result of hypervelocity impact was also observed from ZnS:Cu. The most intriguing conclusion from this research is that it may be possible to discriminate impact velocity by measuring the time-integrated luminosity of TL phosphors. An ability to measure the velocity of a hypervelocity impact is a significant indicator of the potential usefulness for this concept for use as an impact sensor in future spacecraft.     

Photoluminescence enhancement of synthesized ZnS-based-nanocrystals and aging effect on its emitting color

Various colors-emitting ZnS:Cu,Cl, ZnS:Cu,Cl,Mn and ZnS:Mn nanocrystals (NCs) which were shown to be about 3 nm sized-particle were synthesized by using a solution chemistry. And the luminescences of the synthesized ZnS-based NCs were investigated through photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopy. The PLE and PL intensities of the ZnS-based NCs depends on their reflux time, and red shifted maximum PLE wavelengths of the synthesized NCs showed with increasing reflux time. The increased maximum PL intensity of NCs with increasing reflux time is due to the enhanced crystallinity of the NCs. And the shifted emitting colors of the NCs showed after aging treatment compared to those of refluxed NCs. The amount of shifted wavelength of Cu,CI doped ZnS, Cu,CI and Mn co-doped ZnS, only Mn doped ZnS NCs were -22 nm, +18 nm, and +14 nm, respectively.     

核壳结构型ZnS包覆ZnS：Cu的合成及其发光性能研究

利用液相化学方法并添加有机表面活性剂合成了ZnS：Cu／ZnS核壳结构,X射线衍射表明,所合成的ZnS具有闪锌矿结构,随着ZnS包覆量的增加,核壳结构尺寸增大并在紫外-可见光谱图中的吸收峰出现红移,荧光光谱中,该纳米材料在510nm处出现荧光发射峰,主要是由于Cu2＋在t2能级上的复合跃迁。作为表面钝化层,ZnS的包覆有效地降低了晶体中Cu2＋的无辐射复合,并明显改善了znS：Cu的发光强度和发光寿命。     

Photoluminescence and field emission properties of ZnS:Mn nanoparticles synthesized by rf-magnetron sputtering technique

Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size 6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm.     

Pressure dependence of Mn2+ fluorescence in MnS/ZnS core-shell quantum dots

The high pressure photoluminescence spectra of MnS/ZnS core-shells quantum dots were measured using a diamond anvil cell up to 9.4 GPa. Orange emission at 590 nm from the 4T1 --> 6A1 transition of Mn2+ ions was observed. The Mn2+ emission shifted to red with increasing pressure. The experimental pressure coefficient was -48.3 meV/GPa, which is agreement with the calculated value based on the crystal field theory. The redshift is attributed to the increase of crystal field strength and decrease of Racah parameters during compression.     

Temperature dependence of up-conversion luminescence and photoluminescence of Mn2+ in ZnS:Mn2+ nanoparticles

The photoluminescence (excited at both 300 nm and 383.5 nm) and up-conversion luminescence (excited at 767 nm) of the Mn2+ 4T1-->6A1 transition in both bulk and ZnS:Mn2+ nanoparticles have been measured as a function of temperature. The Mn2+ emission spectra shift monotonically to longer wavelengths at lower temperatures, whereas the intensity change of the luminescence is more complex. The complicated temperature behavior is explained by considering the processes of nonradiation relaxation via phonon coupling, exciton thermal dissociation (binding energy), energy transfer, carrier trapping, and the temperature change of the absorption spectra. The fact that the temperature dependence of the 767 nm excited up-conversion luminescence is the same as the 383.5 nm excited photoluminescence in both bulk and nanoparticles supports the conclusion that the up-conversion luminescence is due to two-photon absorption.