Photoluminescence Spectra Of ZnS Research Articles

Suppression of blue photoluminescence and enhancement of green photoluminescence by Mn and Cu Co-doped ZnS quantum dots

ZnS is a good candidate material for making visible light display devices. However, the blue emission of ZnS is so strong in luminescence spectra that it may harm human eyes. In this paper, we prepared the Mn and Cu co-doped ZnS quantum dots, which successfully decreased the blue photoluminescence without producing any Mn-related yellow–orange emissions, and obviously enhanced the eyes-friendly green photoluminescence at the same time. The relevant physical mechanisms have been discussed in detail. Overall, this paper realizes the suppression of blue photoluminescence and enhancement of green photoluminescence of ZnS, thereby the center of whole photoluminescence spectra of ZnS is transferred successfully from blue to green, showing a bright prospect for the application in visible display devices.

Optical and thermogravimetric analysis of Zn1-xCuxS/PVA nanocomposite films

Cu doped ZnS nanoparticles with cubic blend structure had been prepared successfully through thermolysis route and then composited with poly vinyl alcohol using casting method. Zn1-xCuxS/PVA nanocomposites were characterized using different characterization techniques. The quantum dot nature of the ZnS:Cu phase was confirmed by transmission electron microscope technique. Thermal stability was studied by thermogravimetric analysis. The ultra violet measurements illustrated that addition of Zn1-xCuxS nanoparticles to PVA matrix increased the film absorbance. Furthermore, the energy gap and refractive index of the composites were obtained from ultra violet and photoluminescence spectrophotometers. The photoluminescence spectra of ZnS:Cu/PVA nanocomposite films demonstrated a quite broad emission peak at 435 nm with highest photoluminescence intensity in nanocomposite doped with 1% Cu.

Effects of the ZnO layer on the structure and white light emission properties of a ZnS:Mn/GaN nanocomposite system.

ZnO films were inserted between the ZnS:Mn films and GaN substrates by pulsed laser deposition (PLD). The structure, morphology, and optical properties of the ZnS:Mn/ZnO/GaN nanocomposite systems have been investigated. X-ray diffraction results show that there are three diffraction peaks located at 28.4°, 34.4°, and 34.1°, which correspond to the β-ZnS(111), ZnO(002), and GaN(002) planes, respectively. Due to the insertion of ZnO films, the diffraction peak intensity of ZnS:Mn in ZnS:Mn/ZnO/GaN is stronger than that of ZnS:Mn in ZnS:Mn/GaN, and the full width at half-maximum is smaller. Though the transmittance of ZnS:Mn/ZnO films is slightly lower than that of ZnS:Mn films, the transmittance is still higher than 80%. Compared with ZnS:Mn/GaN, an ultraviolet (UV) emission at 387nm (originated from the near-band emission of ZnO) and a green light emission at about 520nm appeared in the photoluminescence (PL) spectra of ZnS:Mn/ZnO/GaN, in addition to the blue emission at 435nm and the orange-red emission at 580nm. The emission at 520nm may be related to the deep-level emission from ZnO and the interface of ZnS:Mn/ZnO.The PL spectrum of ZnS:Mn/ZnO/GaN covers the visible region from the blue light to the red light (400-700nm), and its color coordinate and color temperature are (0.3103,0.3063) and 6869K, respectively, presenting strong white light emission.

Synthesis, characterization and photoluminescence studies of Mn doped ZnS nanoparticles

The present paper reports the synthesis, characterization and photoluminescence (PL) studies of Mn doped ZnS nanoparticles prepared by chemical precipitation method using mercaptoethanol as a capping agent. The nanoparticles were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscope (FEGSEM), and high resolution transmission electron microscope (HRTEM). When the concentrations of capping agent (merceptoethanol) used are 0M, 0.01M, 0.025M, 0.040M, and 0.060M, the sizes of the nanoparticles are 2.98nm, 2.80nm, 2.61nm, 2.20nm and 2.10nm, respectively. Two peaks are obtained in the PL spectra of ZnS:Mn nanoparticles for the excitation wavelength of 220nm, in which the first peak shifts from 400nm to 388nm with decreasing size of nanocrystals, and the second peak lies at 583nm and it does not shift with reducing size of nanocrystals. The PL spectra of ZnS:Mn nanoparticles were measured for different concentrations of merceptoethanol used. The concentration of Mn was kept 1.2%, in which two peaks were found for each sample of ZnS:Mn nanocrystals. The intensities of both the PL peaks increase with reducing size of the nanoparticles. The PL emission centered at 583nm is the characteristics emission of Mn-ion which can be attributed to a 4T1→6A1 transition. However, the blue emission around 400nm is very broad and originates from the radiative recombination involving defect states in the ZnS nanocrystals. Expressions derived for the dependence of PL intensities of peak-I and peak-II on the size of nanoparticles are in good agreement with experimental results.

Effect of capping agent concentration on thermoluminescence and photoluminescence of copper-doped zinc sulfide nanoparticles.

Copper-doped zinc sulfide (ZnS:Cu) nanoparticles with varying concentrations of capping agent were prepared using a chemical route technique. These particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy and X-ray diffraction (XRD). Optical absorption studies showed that the absorption edge shifted towards the blue region as the concentration of the capping agent increased. Using effective mass approximation, calculation of the nanoparticle size indicated that effective band gap energy increases with decreasing particle size. The thermoluminescence (TL) properties of sodium hexameta phosphate (SHMP)-passivated ZnS:Cu nanoparticles were investigated after UV irradiation at room temperature. The TL glow curve of capped ZnS:Cu showed variations in TL peak position and intensity with the change in capping agent concentration. The photoluminescence (PL) spectra of ZnS:Cu nanoparticles excited at 254 nm exhibited a broad green emission band peaking around 510 nm, which confirmed the characteristic feature of Zn(2+) as well as Cu(2+) ions as the luminescent centres in the lattice. The PL spectra of ZnS:Cu nanoparticles with increasing capping agent concentrations revealed that the emission becomes more intense and shifted towards shorter wavelengths as the sizes of the samples were reduced.

Photoluminescence spectra of ZnS:X− (X = F and I) nanoparticles synthesized via a solid-state reaction

ZnS:X− (X=F and I) nanoparticles have been prepared successfully via a solid-state method at low temperature, and the effects of doping with X− on the photoluminescence (PL) properties of ZnS nanoparticles have been investigated. X-ray powder diffraction (XRD), energy-dispersive X-ray spectrum (EDS), transmission electron microscope (TEM), ultraviolet–visible diffusion reflection spectra, and emission and excitation spectra were used to characterize the crystal structure, chemical compositions, diameter, surface states, and optical properties of ZnS:X− (X=F and I) nanoparticles. XRD studies showed the phase singularity of ZnS:X− particles having zinc-blende (cubic) structure with an average crystallite size 4.7–11.0nm. The results indicated that the PL of doping halogen ZnS nanoparticles can be enhanced remarkably by controlling suitable halogen doping, and the most intense emission was obtained when X/Zn=0.3 and 0.45 under 387nm excitation corresponding to X=F and I, respectively. The emission intensity of ZnS:F− (F/Zn=0.3) nanoparticles was higher than that of ZnS:I− (I/Zn=0.45), and exhibited strong emission with an intensity about 9 times higher than the undoped nanoparticles. It was found that the PL of ZnS nanoparticles doped with various halogens was decreased with the increase of the halogen ion radius.

Photo-and Electro-Luminescence in Copper Doped Zinc Sulphide Nanoparticles and Nanocomposites

Copper doped Zinc Sulfide (ZnS:Cu)) is a known green light emitter. Present paper reports luminescence of ZnS:Cu nanoparticles and nanocomposites. Three different nanostructures: mercaptoethanol capped ZnS:Cu nanoparticles, polyvinyl alcohol (PVA) capped ZnS:Cu nanoparticles and ZnS:Cu/PVA nanocomposites have been prepared by chemical route. X-ray diffraction (XRD) revealed cubic zinc blende structure of ZnS:Cu nanocrystals of size below 20 nm. The particle size is found to decrease with increasing capping agent concentration or ZnS loading in PVA matrix. Optical absorption spectra show blue shift in the absorption edge indicating quantum size effect. Photoluminescence (PL) of all the samples was studied by exciting with 212 nm light. The PL spectra of ZnS:Cu/ PVA nanocomposite films show quite broad emission peak at 415 nm where as the PL spectra of mercaptoethanol capped and PVA capped nanoparticles show a very narrow peak at 426 nm and 403 nm respectively. It seems that the nature of passivation of surface states affects the position of surface states. Electroluminescence (EL) studies have shown that light emission starts at a threshold and then increases with voltage. Higher EL intensity and lower threshold voltage is obtained in case of smaller particles. The EL spectra of all the samples are found to be broad with peak at about 420 nm. The EL intensity of ZnS:Cu/PVA nanocomposites is much larger than the ZnS:Cu nanoparticles. The high efficiency EL devices for display and lighting can be fabricated using ZnS:Cu nanocomposites with PVA matrix giving violet emission.

One-Pot and Template-Free Fabrication of ZnS·(ethylenediamine)0.5 Hybrid Nanobelts

A template-free and one-pot solvothermal process has been developed for the facile synthesis of ZnS·(en)0.5 (en = ethylenediamine) hybrid nanobelts having diverse length-to-width (aspect) ratios. While typical hybrid nanobelts synthesized at 180 °C for 6 h have an average width of 130 nm, a mean thickness of 55 nm, and an average length of 16 μm, their aspect ratios have been varied by adjusting solvent volume ratios of hydrazine monohydrate (hm) to en. A sufficient amount of sulfide from the reduction of sulfur by hm has been found to be essential for the efficient anisotropic one-dimensional growth of highly crystalline ZnS·(en)0.5 hybrid nanobelts. The photoluminescence spectra of ZnS·(en)0.5 hybrid nanostructures exhibit three bands located at 327, 415–430, and 587–654 nm, which are assigned to band-edge emission, trap sites-related emission, and anion-vacancy emission, respectively. The mean lifetime of photoluminescence having three decay components of 30, 170, and 2700 ps decreases with the volume ratio of hm to en due to the decrease of defect sites with the increase of the aspect ratios of ZnS·(en)0.5 hybrid nanobelts. Compared with bare-ZnS nanobelts prepared by the hydrothermal treatment of ZnS·(en)0.5 hybrid nanobelts, hybrid ones have shown enhanced optical properties that would give them potential for optoelectronic devices.

Luminescence Properties of ZnS:Cu,Tm Semiconductor Nanocrystals Synthesize by a Hydrothermal Process

ZnS:Cu,Tm nanocrystal with 15nm cubic structures have been synthesized by hydrothermal approach at 200°C. The photoluminescence (PL) properties and the effect of hydrothermal treatment time on the structure, morphology and PL spectra of ZnS:Cu,Tm samples have been studied. The as-obtained samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectra.The result indicated that the PL emission spectrum of codoped with Cu and Tm sample compares with undoped ZnS and doped with Cu alone samples has a significant changes, while the PL emission peak has red shift and PL emission intensity increased. The samples size and crystallization are increase with extending of the treatment time. However, when the hydrothermal treatment time is too long(>12h), the PL emission intensity of sample instead of decreased. Demonstrated changes in surface state of nanomaterials have a greater impact on its luminescence properties.

Brightness-voltage characteristics of ZnS:Mn luminescent films

Brightness-voltage characteristics, the voltage dependence of the luminous efficiency, and the photoluminescence spectra of ZnS:Mn luminescent films produced by thermal and electron-beam evaporation have been studied. Specific features of their properties are attributed to differences in excitation processes of activator centers related to the structural states of the layers.

Solvothermal Synthesis and Photoluminescence Properties of ZnS:Mn2+/ZnO Core–Shell Nanocrystals

High-quality ZnS:Mn2+ and ZnS:Mn2+/ZnO core-shell nanocrystals (NCs) were synthesized via a solvothermal method, and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra. Compared with the bare ZnS:Mn2+ NCs (10 nm), the obtained ZnS:Mn2+/ZnO core-shell NCs have a smaller size (4 nm) and better dispersion, which could be attributed to the added ammonia that adsorbed on the surface of ZnS nuclei and hindered their further growth. From the PL spectrum of ZnS:Mn2+NCs, orange luminescence at about 595 nm is observed, which is attributed to the 4T1-6A1 transition of the Mn2+. Meanwhile, the PL intensity of the ZnS:Mn2+/ZnO core-shell NCs is enhanced, and the emission peak is shifted from 595 to 581 nm. The enhancement of the PL intensity is due to the elimination of the surface defects after the growth of the ZnO shell on ZnS:Mn2+ NCs, while the peak blue shift is mainly ascribed to the stress from the mismatch of lattice constants between ZnS and ZnO NCs.

Photoluminescence decay kinetics of doped ZnS nanophosphors

Doped nanophosphor samples of ZnS:Mn, ZnS:Mn, Co and ZnS:Mn, Fe were preparedusing a chemical precipitation method. Photoluminescence (PL) spectra were obtained andlifetime studies of the nanophosphors were carried out at room temperature. To the best ofour knowledge, there are very few reports on the photoluminescence investigations ofCo-doped or Fe-doped ZnS:Mn nanoparticles in the literature. Furthermore, there isno report on luminescence lifetime shortening of ZnS:Mn nanoparticles dopedwith Co or Fe impurity. Experimental results showed that there is considerablechange 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, 432and 594 nm, while in the case of the ZnS:Mn, Fe nanoparticle sample the peaks areconsiderably different. The lifetimes are found to be in microsecond time domain for 594 nmemission, while nanosecond order lifetimes are obtained for 432 and 411 nm emission inZnS:Mn, X nanophosphor samples. These lifetimes suggest a new additional decay channelof the carrier in the host material.

Mn ion concentration dependence of the photoacoustic and photoluminescence spectra of ZnS:Mn nanocrystals (abstract)

ZnS nanocrystals doped with Mn2+ ions (ZnS:Mn) have attracted much attention in the past few years due to a change in optical properties in accordance with quantum confinement effects. ZnS:Mn nanocrystals exhibit an orange luminescence with a high quantum efficiency (∼18%) under the interband excitation of the host crystals. This spectacular result suggests that the ZnS:Mn nanocrystal system forms a new class of luminescent materials with many applications. To verify the mechanism of high quantum efficiency in ZnS:Mn nanocrystals, it is important to establish the optical absorption characters as an initial step. Few studies have been conducted on light absorption of ZnS:Mn nanocrystals directly because of the difficulty in using of conventional methods caused by strong scattering in the finely powdered structures. The optical absorption spectra of them can be obtained by applying the photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of strongly scattered materials. We will show the PA difference spectra between ZnS:Mn and pure ZnS nanocrystals with different Mn ion concentrations. The peak position corresponds to the transition energy between A16 state (ground state) and E4 state, and it increases with the decrease of Mn2+ ion concentration, indicating a possibility of hybridization of the s–p states of the ZnS host and the d state of the Mn2+ ion. The intensity of optical absorption between those states increases linearly with the increase of Mn ion concentration, indicating that the optical absorption of Mn ion impurities is proportional to the concentration. We have obtained photoluminescence (PL) spectra with different Mn ion concentration. The PL peak of the Mn2+ transition in ZnS nanocrystals (the transition from T14 to A16 states) is 2.08 eV with a half width of 0.24 eV, which is slightly shifted to lower energy region when compared to the peak in the bulk sample, and is independent of the Mn ion concentration. The peak intensity of the PL spectrum shows a maximum, and decreases with higher Mn ion concentration region.

Investigation of the Photoluminescence of Individual Emission Bands of Mn2+ Ions in ZnS Plastically Strained Single Crystals

The photoluminescence spectra of ZnS : Mn plastically deformed single crystals are investigated. It is established that the plastic strain causes the relative concentrations of individual manganese emission centers to change together with conditions of excitation of the centers whose nearest environment has been rearranged upon plastic strain.

Study of optical properties of manganese doped ZnS nanocrystals

ZnS:Mn nanocrystals were prepared by the coprecipitation method. The reaction conditions, such as the amount of manganese doped, the concentration of the reactant, the surfactant, the reactive temperature and time were studied systematically. Nanocrystalline powders and sols exist. The photoluminescent excitation spectra and the photoluminescence spectra of ZnS:Mn nanocrystal were studied by the fluorescent divide spectroscopy under an ultraviolet excitation. It is shown that the luminescent sites of the nanocrystalline powder and sol are different from that of ZnS:Mn bulk crystal. The luminescent site of the sample results from the transition of the doped Mn 2+ in the ZnS crystal.

Effect of MOVPE growth parameters on the photoluminescence linewidth of ZnS xSe 1− x (0⩽ x⩽1) epilayers on GaAs

In this work we report the effect of growth parameters on the properties of ZnS x Se 1– x (0⩽ x⩽1) grown by atmospheric pressure MOVPE. To study the effect of sulphur precursors on the layer quality we use DES or H 2S together with DESe and DEZn as starting materials. The DES is used to grow mirror like ZnS x Se 1– x ( x⩽0.1), whereas higher sulphur contents and mirror-like surfaces were achieved only with H 2S. However, premature reactions between the metalorganic compounds and the H 2S occur. X-ray diffraction measurements and temperature resolved photoluminescence (PL) measurements are used to judge the layer quality. The PL spectra of ZnS x Se 1– x ( x⩽0.1) show sharp excitonic structures; e.g., the FWHM of the I x emission attributed to a donor bound exciton is 1.7 meV in ZnS 0.04Se 0.96. In ZnS x Se 1– x ( x>0.2) the near band edge emission broadens due to alloy fluctuations and increased lattice mismatch. Therefore we obtain a FWHM of only 44 meV at 10 K from ZnS 0.65Se 0.35 layers.