ZnS Host Lattice Research Articles

Eu3+ singly-doped and Eu3+/Sm3+ co-doped ZnS quantum dots: structure, optical properties and energy transfer.

In this study, Eu3+ ion singly doped and Eu3+/Sm3+ ions co-doped ZnS semiconductor quantum dots (QDs) were successfully synthesized using a wet chemical method in 1-octadecene (ODE) solvent. The successful doping of Sm3+ and Eu3+ ions into the ZnS host lattice and the composition and valence of the elements present in the sample were confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Structural and morphological studies revealed the presence of Eu3+-doped ZnS and Eu3+/Sm3+ co-doped ZnS QDs of about 3-4 nm size with a zinc blende structure. The Judd-Ofelt (J-O) intensity parameters of Eu3+-doped ZnS QDs were determined from their fluorescence spectra. The optical properties of Eu3+/Sm3+ co-doped ZnS QDs were studied by changing the Eu3+ ion concentration and fixing the Sm3+ ion concentration. The photoluminescence (PL) spectra of Eu3+/Sm3+ co-doped ZnS QDs were obtained at an excitation wavelength of 403 nm (6H5/2 → 6P3/2 transition of Sm3+ ions) in the 525-725 nm range. The effective energy transfer (ET) process from Sm3+ to Eu3+ ions was confirmed and explained in detail using the Reisfeld approximation and the Inokuti-Hirayama model. The CIE color coordinates of the Eu3+/Sm3+ co-doped ZnS QDs were obtained using PL spectral data. Eu3+/Sm3+ co-doped ZnS QDs exhibited a long lifetime and emitted warm red light. These interesting properties give Eu3+/Sm3+ co-doped ZnS QDs great potential for applications in photovoltaics, photocatalysis, and biomarkers.

Sunlight-assisted photocatalytic degradation of tartrazine in the presence of Mg doped ZnS nanocatalysts

In this work, Mg2+ doped ZnS nanoparticles were prepared by solvothermal method, using ethanol as solvent at 135 °C.The nanoparticles were characterized by XRD, SEM, UV–vis and PL. After doping, XRD revealed a reduction in lattice parameter, confirming Mg2+ substitution into the ZnS host lattice. The UV–vis study indicated that the incorporation of Mg2+ ions does not modify the band gap width of the nanoparticles. The PL spectra measured at 325 nm excitation wavelength, reveals that the photogenerated electrons of Zn0·9Mg0·1S have a slower recombination rate than ZnS nanoparticles. The XPS finding confirm that the chemical environment of the elements has been affected by the presence of the Mg2+. The Valence Band Maximum (VBM) was determined to be 0.2eV for ZnS and 1eV for Zn0·9Mg0·1S, respectively. These findings confirm the perturbation of electronic properties when Mg2+ is added to the ZnS. The photocatalytic ability was estimated through the degradation of tartrazine under natural-sunlight irradiation. Zn0.9Mg0.1S shows a high photocatalytic activity, compared to ZnS nanoparticles. The photocatalytic degradation was studied through different parameters, such as: the source of irradiation, the pH, the dye concentration, the catalyst concentration, and the recyclability. The degradation investigation shows that tartrazine is better oxidized at free pH = 6,7, with a dye concentration of 20 mg/L and a catalyst dosage of 1 g/L. Zn0.9Mg0.1S degraded 98% of tartrazine under natural-sunlight irradiation. In addition, the catalyst retained a good photo-degradation capacity, even after many treatment cycles. The scavengers study confirmed that the main active species responsible for the photocatalytic degradation of tartrazine were the oxidation groups (O2•-).

Green synthesis of magnetically recyclable Mn0.6Zn0.4Fe2O4@Zn1-xMnxS composites from spent batteries for visible light photocatalytic degradation of phenol

Magnetic binary heterojunctions are a kind of promising photocatalysts due to their high catalytic activity and easy magnetic separation; however, their synthesis may involve high costs or secondary environmental impacts. In this work, the magnetically recyclable Mn0.6Zn0.4Fe2O4@Zn1-xMnxS (MZFO@Zn1-xMnxS, x = 0.00–0.07) photocatalysts are synthesized from spent batteries via a green biocheaching and egg white-assisted hydrothermal method. The as-synthesized photocatalysts have been comprehensively characterized in phase, morphology, texture, optics, photoelectrochemistry and photocatalytic activity. Characterization results indicate that the desired core-shell structure MZFO@Zn1-xMnxS composites are successfully synthesized, theirs absorption intensity in the visible light region is greatly enhanced compared to Zn1-xMnxS. In addition, doped Mn2+ in ZnS host lattice and the staggered bandgap alignment of MZFO and Zn1-xMnxS greatly enhances electron transfer and charge separation in the binary heterojunction system. The optimized MZFO@Zn0.95Mn0.05S shows the highest photodegradation performance toward phenol under the visible light irradiation, with a complete degradation of 25 mg L−1 of phenol within 120 min, and its reactive kinetic constants is about 5.2 and 13.3 times higher than that of pure Zn0.95Mn0.05S and MZFO, respectively. Furthermore, the mechanism and pathways for the degradation of phenol are proposed. In addition, MZFO@Zn0.95Mn0.05S also exhibits a good reusability and high magnetic separation properties after 5 successive cycles. This new material has the advantages of low costs, simple reuse and great potential in application.

Optical properties of Ce3+ and Tb3+ co-doped ZnS quantum dots

Ce3+ and Tb3+ co-doped ZnS quantum dots (QDs) were synthesized using a facile and effective wet chemical method. The effect of Tb3+ concentration on the structure and optical properties of the co-doped QDs was explored thoroughly using various characterization methods. The chemical composition and oxidation state of the elements in the synthesized QDs were examined by X-ray photoelectron spectroscopy (XPS). The crystal structure and luminescence properties of the synthesized QDs were investigated using X-ray diffraction (XRD) and photoluminescence (PL). The change in the crystal structure of the Ce3+ and Tb3+ co-doped QDs with an increase in the concentration of Tb3+ dopant from 1% to 8% was observed for the first time. The excitation spectra of Ce3+ and Tb3+ co-doped QDs were investigated using the photoluminescence excitation (PLE) technique. The energy transfer (ET) from Ce3+ to Tb3+ ions in the ZnS host lattice occurred effectively because of the large spectral overlap between the emission band of Ce3+ and the excitation band of Tb3+ ions. The observed properties revealed that doping with Ce3+ enhanced the energy transfer process and the interaction mechanism in energy transfer was dominated by dipole-dipole interaction. The thermal stability of the co-doped QDs was explored by studying their PL spectra in the temperature range of 15–300 K. Ce3+ and Tb3+ co-doped ZnS QDs exhibited a very long decay time on the order of ms. The valuable optical properties of Ce3+ and Tb3+ co-doped ZnS QDs make them potentially useful for photovoltaic, photocatalyst, and biosensing applications.

Synthesis of capped Cr-doped ZnS nanoparticles with improved bactericidal and catalytic properties to treat polluted water

Inorganic semiconducting ZnS doped with Cr nanoparticles was fabricated using chemical co-precipitation method with monothioethylene glycol as capping agent. This study is an effort to investigate as to how various concentration ratios of systematically doped Cr (1, 3, 5, and 7 wt%) to ZnS affect structural, optical, and morphological properties at room temperature. Powder X-ray diffraction (XRD) studies revealed that crystallinity improved upon doping and the synthesized material has cubic structure without secondary phase. XRD and Raman spectra showed successful incorporation of Cr3+ particles into ZnS host lattice. The functional groups and chemical species associated with vibration of molecules were determined with Fourier transform infrared spectroscopy (FTIR). Field-emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HR-TEM) images showed nanoscale particles with cubic and spherical morphology. Elemental composition of Cr-ZnS particles was determined using energy-dispersive X-ray (EDX) spectroscopy. Kinetics of degradation of methylene blue (MB) catalyzed via synthesized nanoparticles was recorded under UV–Vis irradiation. The antimicrobial evaluation of Cr-doped ZnS nanocomposites against MDR S. aureus showed significant (p < 0.05) inhibition zones compared to undoped ZnS. The catalytic activity results indicate that ZnS is an efficient nanocatalyst that could be effectively used for the removal of environmental pollutants.

Effects of structure on photoluminescence characteristics of Mn2+-doped ZnS quantum dots for anti-counterfeiting ink application

The zinc-blende-to-wurtzite transition of thioglycolic acid (TGA)-capped ZnS:Mn2+ QDs prepared at 80 °C in air has been observed with the increasing TGA/Zn2+ ratios. Effects of structure on the photoluminescence characteristics of ZnS:Mn2+ QDs were studied in this paper. The relative PL intensity ratio of the Mn2+ orange-red emission and the ZnS blue emission (IOE/IBE) and color purity (CP) (CP ≈ 65.6%) were maximum with the optimal molar ratio of TGA/Zn2+ = 3, which indicate the efficient transmission of excitation energy from the ZnS host to the Mn2+ impurity. Furthermore, the investigated result shows that the energy transfer in the cubic ZnS host lattice is more efficient than that of the hexagonal ZnS and the color correlated temperature (CCT) values increase with increasing the TGA/Zn2+ ratio. The crystal field strength (Dq) values of ZnS:Mn2+ QDs decrease from 603 cm−1 to 455 cm−1 with the increasing of the TGA/Zn2+ ratio from 0 to 6, respectively. The ZnS:Mn2+ QDs were applied in anti-counterfeiting ink, which was written on a glass sheet. The image was then excited by normal light and 385 nm UV light excitation, which emitted orange-red color with the UV light excitation. These investigated results can be particularly suitable for security ink applications or optoelectronic devices. Moreover, the zinc-blende-to-wurtzite phase transition in this study will be of great importance for the family of ZnS-based doped quantum dots.

XAS Microstructure Analysis of Manganese Doped Zinc Sulphide Nanophosphor

This paper reports wet chemical synthesis of Manganese doped Zinc Sulphide Nanophosphors capped with polyvinyl alcohol (PVA) while varying the concentrations of the dopant and capping agent to explore the optoelectronic and microstructural properties. Optical and morphological comparative studies reveal strongest room temperature orange luminescence (∼591 nm) of 10% dopant concentration with 2% capping agent in the ZnS host lattice and irregularly spherical nanoparticles formation (∼29 nm). Further, structural and elemental study of the sample reveals uncontaminated hexagonal wurtzite nanoparticles with least structural distortion due to dopant induced substitutional defect. The XANES and EXAFS microstructure analysis confirm the creation of substitutional defect and comparable Zn-S and Mn-S bond lengths such that Mn luminescent centers are created. Hence, the detailed study of the material indicates its high efficiency, proving its ability to be explored as a strong candidate for Mn: ZnS based UV Photodetector devices.

Electronic Structure and Ferromagnetism in Zincblende Zn1−xCoxS Nanoparticles

We have prepared Zn1−xCoxS nanoparticles (NPs) and studied their local-geometric, electronic, and magnetic properties. X-ray diffraction analyses have indicated that NPs with average crystallite sizes of 2.2 ∼ 2.9 nm are single phase and crystallize in the zincblende-type structure. Cobalt ions with oxidation state + 2 (Co2+) replaced for Zn2+ and almost unchanged the zincblende-type structure of the ZnS host lattice. Interestingly, all samples show room-temperature ferromagnetism and ferromagnetic order increases with increasing Co content (x) in Zn1−xCoxS NPs. With the results obtained from analyzing the local-geometric structures at Zn and Co K-edges and photoluminescence spectra, we believe that ferromagnetism in Zn1−xCoxS NPs is related to intrinsic defects and exchange interactions between Co2+ ions. We have also reviewed the recent studies on ZnS-based dilute-magnetic materials.

Energy transfer in poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots

Poly(vinyl alcohol) (PVA)-encapsulated Mn2+-doped ZnS quantum dots (PVA-ZnS:Mn2+ QDs) synthesized at 80 °C in air. The structural property was investigated using X-ray powder diffraction (XRD). The XRD analysis shows that the ZnS:Mn2+ QDs possessed a zinc blende structure and the complexes of ZnS:Mn2+ QDs with PVA molecules have been formed. The photoexcitation energy transfer is found and investigated between PVA molecules and ZnS:Mn2+ QDs using characterization techniques such as Fourier transform infrared spectroscopy (FTIR), UV–vis absorption spectroscopy, photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopy. The studied results show the photoluminescence enhancement of the Mn2+ 4T1(G) – 6A1(S) emission intensity is due to the efficient energy transfer process from the ZnS host lattice and PVA capping molecules to Mn2+ centers. Moreover, Förster resonance energy transfer (FRET) efficiency from PVA molecules to the Mn2+ center within PVA-ZnS:Mn2+ QDs is about 20.28%.

Structural, photoluminescence and magnetic properties of Mn, Cr dual-doped ZnS quantum dots: Influence of Cr concentration

Mn-doped ZnS and Mn, Cr dual-doped ZnS quantum dots were prepared using a simple co-precipitation method. The synthesized samples were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-rays (EDX), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy, photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). Cr doping reduced the crystallite size. The reduction of activation energy due to the incorporation of Cr is responsible for the increase of micro-strain and the suppression of crystallite size. The change in lattice parameters by Cr doping is attributed to the replacement of Cr3+/Cr2+ ions instead of Zn2+ ions in the ZnS host lattice. Doping concentration of the samples was confirmed by energy dispersive X-ray (EDX) spectra. Occurrence of higher intensity in absorption and a shift in absorption edge towards the lower angle side were supported by the proper substitution of Cr2+ ions instead of Zn2+ ions in the ZnS host. The diminishment of absorption intensity for Cr doping beyond 2% can be ascribed to defect states caused by imperfections in the lattice structure due to the different sizes of Cr2+/3+, Mn2+ and Zn2+. When Cr is introduced into the Zn-Mn-S assembly, a shift in UV emission is observed from 392 nm to 379 nm for Cr = 2% and 382 nm for Cr = 4%; these peak shifts were due to the size effect and the change in crystal structure by Cr doping. Nevertheless, the magnetic moment is enhanced because of the increase in number of spins by Cr incorporation; all samples retained their paramagnetic nature.

Terbium-doped ZnS quantum dots: Structural, morphological, optical, photoluminescence, and photocatalytic properties

Terbium (0, 2, and 4 at%)-doped ZnS quantum dots (QDs) were synthesized via a solvothermal method. The crystal structures of the synthesized QDs were determined to be zinc blend by X-ray powder diffraction (XRD) and Raman analyses. Transmission electron microscopy (TEM) studies revealed that particles with a mean size of 2–4 nm were formed. An X-ray photo electron spectroscopy (XPS) examination disclosed the existence of terbium with a trivalent state in the ZnS host lattice. The absorption bands of all QDs were located around 325 nm (3.81 eV) and were higher than that of the bulk ZnS band gap (3.67 eV), consistent with the quantum confinement effect. The photoluminescence spectra of the terbium-doped samples displayed five emission peaks at 467 nm (5D4→7F3), 491 nm (5D4 → 7F6), 460 nm (5D4 – 7F5), 484 nm (5D4 – 7F4), and 530 nm (5D4 – 7F3), respectively. The terbium-doped QDs exhibited a higher photocatalytic activity during the degradation of crystal violet dye under UV-light illumination compared to the undoped ZnS QDs. These interesting properties of terbium-doped ZnS QDs are potentially useful for both luminescent and photocatalysis applications.

Influence of Co2+ on electrical and optical behavior of Mn2+-doped ZnS quantum dots

Co2+-doped Zn0.98Mn0.02S quantum dots with various concentrations of Co2+ from 0% to 4% have been successfully synthesized by a simple co-precipitation method. X-ray diffraction (XRD) pattern confirmed the acquirement of cubic structure and phase purity in all the samples. The average crystallite size of the particles was ∼3 nm observed from XRD result. Surface morphology of the samples was studied using scanning electron microscope (SEM). TEM study was also taken to know the structural parameters of the samples. Fourier transform infrared (FTIR) spectra proved the presence of Co2+ and Mn2+ in ZnS host lattice. Energy dispersive X-ray (EDX) analysis confirmed the elemental composition with their normal stoichiometric ratio. In the dielectric study, dielectric dispersion and dielectric loss were increased with Co2+ composition due to the increase of carrier concentration. From the AC conductivity measurement, the maximum conductivity was observed for Co2+ = 2% due to their higher charge carrier density and it was decreased for Co2+ = 4% due to the scattering of charge carriers. Because of the low dielectric constant at higher frequency, these materials can be used for high-frequency applications. The variation of peak intensity and wavelength shifting in UV-vis absorption and transmittance were discussed on the basis of formation of secondary phase and variation of charge carrier density. The continuous red shift of energy gap by Co2+-doping is attributed to the direct energy transfer between excited states and 3d levels of Co2+ ions. Photoluminescence spectra showed the strong and broad blue emission bands between 468 nm and 483 nm. Since higher transmittance was observed for Co2+ = 2% addition, this material can be selected for optimum applications of optoelectronic devices.

Investigations on photoluminescence enhancement of poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots

In our work, we focused on the photoluminescence (PL) enhancement of poly(vinyl alcohol) (PVA)-encapsulated Mn2+-doped zinc sulfide quantum dots (ZnS:Mn2+ QDs) synthesized at 80°C in basic aqueous solutions. The structural, morphological and optical properties were investigated using characterization techniques such as X-ray powder diffraction (XRD), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis absorption and photoluminescence (PL) spectroscopy. According to the results of UV–vis absorption spectra, the optical bandgap of the quantum dots was higher than that of the bulk ZnS due to the quantum confinement effect. The studied result showed that the Mn2+ 4T1 → 6A1 emission intensity at the wavelength of 600nm significantly increased with the increase of Mn2+ doping content and reached its maximum value at the Mn2+ concentration of 4.5%. In addition, the effect of PVA/Zn2+ molar ratio on the PL enhancement of PVA-encapsulated Mn2+-doped ZnS quantum dots also was systematically investigated and explained in this paper. The studied results indicated the energy transfer process from the ZnS host lattice and PVA capping molecules to Mn2+ centers is more efficient at the optimal PVA/Zn2+ molar ratio of 3 × 10−4. Furthermore, a mechanism for the formation of the PVA-encapsulated Mn2+-doped ZnS quantum has also been suggested in this study.

Investigation of Ni influence on structural and band gap tuning of Zn0.98Mn0.02S quantum dots by co-precipitation method

Zn0.98−xNixMn0.02S (x = 0, 0.02, 0.04) quantum dots have been synthesized by using simple co-precipitation method. The synthesized samples were characterized using various analytical tools to monitor optimum properties. X-ray diffraction analysis revealed that the materials had cubic crystal structure as well as phase purity. The average crystallite size was determined within the range of 1.3 to 1.8 nm using Debye Scherer equation. The microscopic studies showed the smooth surface passivation and agglomeration of particles. Energy Dispersive X-ray analysis ensured the existence of compositional elements, Zn, Ni, Mn and S in the synthesized samples within the stoichiometry ratio. UV–Visible absorption and transmittance studies and band gap estimation were taken from optical studies. The optical studies showed the red shift in absorption and elevation of intensity by increasing Ni concentration. The band gap of the samples was found to be in the range of 3.56–3.93 eV (red shift) because of the exchange interactions between Zn (3d10) and localized d electrons of Mn (3d5) and Ni (3d8). From the observation of linear red shift of band gap, substantial absorption and low transmittance by Ni incorporation, this material can be chosen as a suitable applicant for the optoelectronic device applications and as a buffer material for the solar cell applications. FTIR spectrum report confirmed the presence of the dopant into the ZnS host lattice and chemical bonding corresponding to each elements in the prepared samples.

Structural and magnetic properties of ZnS:Tb3+ nanoparticles

ZnS:Tb3+ (0, 1, 3, and 5 at.%) NPs were synthesized via a hydrothermal method using polyethylene glycol as a stabilizer. The prepared samples were characterized systematically using various characterization techniques, such as energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry .The XRD studies showed that all of the samples exhibited a cubic structure without any secondary phases. The formation of ultrafine (<5 nm) nanoparticles was confirmed by the HRTEM analysis. XPS revealed that the Tb ions are incorporated into the ZnS host lattice as trivalent ions. Room temperature magnetic measurements of the doped samples show the transformation from ferromagnetism to superparamagnetism with increasing doping concentration. This could be due to the antiferromagnetic interaction between the nearest neighboring Tb–Tb ions in the ZnS host lattice.

Synthesis and luminescence properties of ZnS: [formula omitted], [formula omitted], [formula omitted] nanophosphors

The Zn(1−(2x+y))S: Cex=0.0013+Lix=0.001+Mn(0.001≤y≤0.03)2+ nanophosphors were prepared using simple chemical ionic mixing method at room temperature. The X-ray diffraction studies on the undoped and doped samples confirmed the formation of zinc-blende structure. As the codopant concentration was increased the band gap energy gradually decreased from 3.92 eV to 3.86 eV. The Zn0.999S:Ce0.0013+ nanophosphor showed the defect emission in the blue and green region with the peak positions at 429 nm, and 539 nm and 564 nm respectively. The Zn(1−(2x+y))S: Cex=0.0013+Lix=0.001+Mn(0.001≤y≤0.03)2+ samples showed a defect emission at 400 nm along with the Mn2+ emission at 590 nm. The orange emission was due to de-excitation of electrons from [4T1(4G)−6A1(6S)]3d5 unfilled shell of Mn2+ ions in ZnS host lattice. The ZnS: Ce3+, Li+, Mn2+ nanophosphors show white light, as confirmed by the CIE chromaticity coordinates (0.374, 0.332).

The structure and multifunctional behaviors of Mn–ZnO/Mn–ZnS nanocomposites

Mn–ZnO/Mn–ZnS nanocomposites have been synthesized by using Mn–ZnO nanorods as templates through a simple sulfidation reaction. The incorporated Mn dopants are in 2+ valence state and substitute for Zn2+ ions in both ZnO and ZnS host lattice. The Mn–ZnO nanorods display robust ferromagnetism as well as weak ultraviolet and visible emissions at room temperature. The coating of Mn–ZnS layer results in the decrease of ferromagnetism and the significant enhancement of visible emission in orange region. Meanwhile, the band gap of the nanocomposites increases as the sulfidation time prolongs. By studying the variation of ferromagnetism with the sulfidation time, it is concluded that the observed strong ferromagnetism in Mn–ZnO nanorods mainly originates from the surface region where the ferromagnetism is much stronger relative to the core area of the nanorods.

EDTA-assisted hydrothermal synthesis, characterization and photoluminescent properties of Mn2+-doped ZnS

In this paper, undoped ZnS and Mn2+-doped ZnS nanocrystals were synthesized through a facile EDTA-assisted hydrothermal method. The as-synthesized powder samples were systematically characterized by employing the following characterization technique such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), UV–visible optical absorption and photoluminescence (PL) spectroscopy. X-ray diffraction pattern revealed the presence of material in single phase with average crystallite size of about 3nm and the material remained cubic over the whole Mn solid solution range. Formation of ultrafine, spherical and homogeneous dispersed nanoparticles with size 4nm was confirmed by HRTEM analysis. Absorption shoulders of the samples were blue-shifted as compared to bulk ZnS (3.6eV) with decrease in the energy band gap as the Mn concentration increases. The room temperature photoluminescence (PL) spectra of Mn2+-doped ZnS nanocrystalline showed extra peaks in yellow–orange and red region in comparison of pure ZnS. Mn induced PL was suggested with the significant enhancement of the PL intensity in ZnS:Mn nanocrystalline due to Mn incorporation. The red shift in the yellow–orange emission peak can be attributed to the change in band structure due to the formation of ZnS:Mn alloy with increase in Mn2+ concentration. The yellow–orange emission peak corresponds to the 4T1(excited)–6A1(ground) transition of Mn2+ ion in Td symmetry in the ZnS host lattice. The emission peak in the red region may be due to Mn2+ d–d transitions in (Zn Mn)S matrix as some of the nearest neighbors of Mn2+ are now predominantly S atoms due to their random positioning nature in the nanocrystallite and Mn–Mn interaction at high Mn2+ concentration. This type of doped semiconductors with multi-band emission can be made bioactive when they are linked with suitable biomolecules.

Hydrothermal synthesis of wurtzite Zn1−xNixS mesoporous nanospheres: With blue–green emissions and ferromagnetic Curie point above room temperature

Wurtzite Zn1−xNixS (x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) mesoporous nanospheres were successfully synthesized via a versatile hydrothermal method with the assistance of ethylenediamine (EN). The as synthesized nanospheres were uniform, mono-dispersed with a spherical shape. Microstructure investigations revealed that these nanospheres were mesoporous clusters of Zn1−xNixS nanoparticles with the size around 5nm. X-ray Diffraction, X-ray photoelectron spectroscopy, and Energy-dispersive X-ray spectroscopy studies confirmed that the Ni ions substituted into ZnS host lattice without altering the crystal structure. The Fourier-transform infrared spectra confirmed the coupling between the EN molecules and ZnS. The absorption edge in the diffuse reflection spectra shifted towards lower wavelength with increasing Ni concentration, indicating an expansion in the band gap energy that is estimated to be in the range of 3.53–3.60eV. The photoluminescence spectra of the doped and un-doped samples contained a broad emission band covering the range of 350–650nm. Room temperature magnetization studies indicated that the undoped ZnS nanospheres yielded only diamagnetism, whereas the doped samples exhibited ferromagnetism that can be attributed to the Ni2+ dopants. The temperature dependence of magnetization revealed that the Zn1−xNixS nanospheres have Curie point above room temperature. The intrinsic ferromagnetism and ferromagnetic Curie point above room temperature promise a great deal of potential applications in spintronic devices for Zn1−xNixS nanospheres.

Magnetism and photoluminescence of Mn:ZnO/Mn:ZnS heterostructures

Mn:ZnO/Mn:ZnS core–shell heterostructures, in which Mn2+ ions are incorporated into ZnO and ZnS host lattice by replacing Zn2+ ion sites, have been synthesized by coating single-crystalline Mn:ZnO nanorods with a thin layer of Mn:ZnS nanocrystals. The heterostructures possess visible/ultraviolet photoluminescences and intrinsic room-temperature ferromagnetism. Photoluminescent spectrum exhibits enhanced ultraviolet emission of Mn:ZnO, defect-related green emission of Mn:ZnS, and strong orange emission due to 4T1(4G)–6A1(6S) transition of Mn2+ in ZnS. A strong ferromagnetic layer is found to exist on the surface of the Mn:ZnO core, which makes a much larger contribution to the macroscopic ferromagnetism of the heterostructures.