Mn-doped ZnS Nanoparticles Research Articles

The effect of ultraviolet irradiation on the photothermal, photoluminescence and photoluminescence excitation spectra of Mn-doped ZnS nanoparticles

Research involving Mn doped nanocrystalline ZnS (ZnS:Mn) has grown in recent years, partly due to the high quantum luminescence efficiencies that have been reported. We measured the photoacoustic (PA), the photoluminescence (PL) and the photoluminescence excitation (PLE) spectra of surface-passivated and unpassivated ZnS:Mn. The effects of UV irradiation on the PL and PLE spectra were also studied. A decrease in the PA intensity after UV exposure was observed for the ZnS:Mn, indicating a decrease in the nonradiative relaxation probability. The observed increase in PL intensity indicates a corresponding increase in the radiative transition probability. For the PLE spectra, possible aggregation of the primary particles could have resulted in the lower measured energy of the PLE peak compared to the value predicted by the effective mass approximation theory.

Studies on the effect of UV irradiation on Mn-doped ZnS nanoparticles

With the advent of the increased attraction in compound semiconductors, attention has been focused on the research involving nanocrystalline Mn 2+ doped ZnS (ZnS : Mn). In this paper, nano-scaled ZnS : Mn (both unpassivated and pasivated samples) was synthesized and we report the photoacoustic (PA) as well as photoluminescence (PL) properties upon exposure to ultraviolet (UV) light. It was found that passivation with acrylic acid (AA) yielded higher photoluminescence intensity. UV exposure caused a decrease in the PA intensity observed owing to a decrease in the nonradiative processes during exposure. A corresponding increase in the radiative processes was verified with the increase in the PL intensity during UV exposure. These experimental results suggest the possibility of UV curing for the passivating AA monomer and photochemical reactions around the nanocrystals, indicating the increase of the fluorescence quantum efficiency. Luminescent time decay measurements for the sample without AA showed a lengthening in the time decay constant after UV exposure. On the other hand, for the sample with AA, no change in the time decay constants was observed. This further strengthens the theory that during UV exposure, different luminescent decay mechanisms exist for the unpassivated and passivated samples.

Photoacoustic and Photoluminescence Characterization of Passivated and Unpassivated Mn-Doped ZnS Nanoparticles

In this study, passivated and unpassivated nanocrystalline ZnS with varying Mn2+ concentrations (ZnS:Mn) were synthesized and their photoacoustic (PA) and photoluminescence (PL) characteristics were studied. The PA intensity peak for the nanocrystalline ZnS was found to be blue-shifted compared with that for the bulk material due to quantum confinement effects. The difference of the PA signals of doped ZnS and undoped ZnS yielded the Mn2+ optical absorption spectra. The intensity of the PA peak increased linearly with Mn concentration. The PL spectra showed a peak position at 2.08 eV corresponding to the d–d transition of Mn2+. For the unpassivated sample, a decrease in the PL intensities for higher Mn concentrations was observed. This could be attributed to concentration quenching. Addition of acrylic acid as a passivator led to an increase in PL intensity for all Mn concentrations and prevented the decrease in the PL intensity for higher Mn concentrations. These could be attributed to the surface passivation, which reduces the nonradiative recombination probabilities, thus increasing PL intensities.

Synthesis and size control of monodisperse manganese-doped ZnS nanoparticles by methacrylate polymer

A simple route to the fabrication of methacrylate polymer containing Mn-doped ZnS nanoparticles is described. The particles prepared have sizes as small as 1.8–2 nm, capped or modified by methacrylate polymer, and the thermal, mechanical, chemical stability, life and luminescence intensity are greatly improved. The particle sizes can be easily controlled by changing the number-average degrees of polymerization, which can be realized by adjusting the molar ratio of monomer to chain-transfer agent.

Properties and reactivity of Mn-doped ZnS nanoparticles

The physico-chemical properties and reactivity of ZnS:Mn (1% Mn) nanoparticles were investigated. ESR, XRD, specific surface area and reactivity in H 2SO 4 were studied in order to elucidate the degree of distribution of Mn atoms. There is a strong correlation between preparatory history, the shape of ESR spectra and reactivity of ZnS:Mn nanoparticles.

Synthesis of TOPO-capped Mn-doped ZnS and CdS quantum dots

TOPO (tri-n-octylphosphine oxide) capped Mn-doped ZnS and Mn-doped CdS nanoparticles have been prepared from bis(diethyldithiocarbamato)zinc(II) or bis(methylhexyldithiocarbamato)cadmium(II) and manganese dichloride. The nanoparticles obtained all show quantum size effects in their optical spectra with respect to the parent CdS and ZnS. There are clear differences in the photoluminescence of the ZnS (448 nm) and ZnS∶Mn (510 nm) samples. The level of Mn-doping can be differentiated by the photoluminescence intensity, all of the doped samples show an emission maximum at 510 nm. EPR spectra and ICP results confirm the quantitative incorporation of manganese into the ZnS quantum dots. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and transmission electron microscopy (TEM) show the material to be hexagonal. The crystallinity of the material was also evident from high resolution transmission electron microscopy (HRTEM) which gave well-defined images of particles with clear lattice fringes. The PL spectrum of the doped CdS nanoparticles has an emission maximum at 585 nm as is usually attributed to the 4T1–6A1 electronic transition of manganese in a tetrahedral site. However the PL spectrum changes over time (weeks) to give a spectrum typical of the deep trap emission of CdS. SAED and XRD show both CdS and the Mn-doped CdS particles to be in the hexagonal phase. TEM and high resolution TEM show images of nanosize particles with clear lattice fringes. EPR spectra and ICP results confirm the presence of manganese in the CdS nanoparticles. EPR spectra showed that CdS∶Mn was not stable over longer periods of time with segregation of manganese at the surface of particles in older samples of CdS. By contrast, the ZnS∶Mn samples were quite stable for several weeks.

Luminescence decay kinetics ofMn2+-doped ZnS nanoclusters grown in reverse micelles

We report the synthesis and luminescence decay kinetics of 1.2-nm ${\mathrm{Mn}}^{2+}$-doped ZnS nanoclusters grown in reverse micelles. The preparation method produces small particles with narrow-size distribution and fluorescence bands near 400--450 nm and 585 nm. Time-dependent fluorescence decay measurements using picosecond, nanosecond, and millisecond techniques reveal relaxation processes on all three time scales. In the doped sample, the red emission detected at 600 nm exhibits a 1--2 ms decay in addition to faster decays with time constants on the order of hundreds of ps, a few ns and tens of \ensuremath{\mu}s. While the slow decay is the same as that of bulk ${\mathrm{Mn}}^{2+}$-doped ZnS, the fast decays are present for both doped and undoped samples and are unique to nanocluster ZnS, which are attributed to deep trap-state emission. The blue luminescence near 400--450 nm is attributed to shallow trap-state emission of ZnS. These results help to resolve the controversy in the literature regarding the lifetime of the ${\mathrm{Mn}}^{2+}$ emission in Mn-doped ZnS nanoparticles.

Mn-doped ZnS nanoparticles as efficient low-voltage cathodoluminescent phosphors

We have synthesized nanoparticles of ZnS doped with Mn for potential use as cathodoluminescent phosphors in field-emission displays (FEDs). We show that the cathodoluminescent efficiency of particles ⩽100 nm in diameter is within 40% of that of a commercial (micron-sized) phosphor when the electron-beam energy ranges between 500 and 3500 eV. The nanoparticles exhibit less current saturation than larger-sized phosphors, an important feature for use in FEDs. Furthermore, the nanoparticles were annealed at just 535 °C, hundreds of degrees below the processing temperatures of standard phosphors. Finally, we discuss the effect of the particle surface on low-voltage luminous efficiency.

Enhanced Photoluminescence and Characterization of Mn-Doped ZnS Nanocrystallites Synthesized in Microemulsion

ZnS:Mn luminescent nanomaterials were first prepared in an inverse microemulsion at room temperature as well as under a hydrothermal condition. Mn-doped ZnS nanoparticles obtained are distributed from 3 to 18 nm in diameter as determined by transmission electron microscopy. The crystalline nature of the materials is clearly demonstrated by the X-ray diffraction results. Compared with Mn-doped ZnS materials synthesized through the conventional aqueous reaction, the nanoparticles prepared in a microemulsion show a significant enhancement in photoluminescence. In particular, the photoluminescence of particles prepared in microemulsion under hydrothermal treatment was found to be enhanced by a factor of 60 as compared to that of the material obtained through the direct aqueous reaction at room temperature. This dramatic increase in photoluminescence yield is attributed to the surface passivation of nanoparticles by the adsorption of surfactants in microemulsion, the formation of sphalerite with cubic zinc ble...

Optical properties and characteristics of ZnS nano-particles with homogeneous Mn distribution

Unique properties of nano-particles of Mn-doped ZnS prepared by a new chemical process are studied. Homogeneously Mn-doped ZnS nano-particles, as demonstrated from electron spin resonance (ESR), were accomplished by precipitation in a methanolic media with the aid of methacrylic acid at room temperature. Photoluminescence (PL) intensity of ZnS nano-particles increased with decreasing particle size. Quantum size effects were confirmed from the blue shift in the optical band gap of ZnS nano-particles. The enhanced PL intensity was also explained by the nanosize effect.