Optical properties of oxide magnetic ZnO, Zn0.95Mn0.05O and Cu2O nanopowders

ZnO, Zn_0.95Mn_0.05O and Cu₂O nanocrystals are synthesized. Excitonic lines in absorption spectra of these materials are detected. In photoluminescence and photoluminescence excitation spectra of Zn_0.95Mn_0.05O the dangling bond hybrid (DBH) state is found. It has splitted out from the top of the valence band due to the hybridization between d-states of the Mn impurity and the p-states of oxygen.     

Luminescence and vibration spectra of zinc manganese diphosphates

The synthesis conditions for new luminescent materials, zinc manganese diphosphates Zn_{2? x}Mn_xP₂O₇ · 5H₂O) (0 ≤ x ≤ 2.0), are considered. The photoluminescence and its excitation spectra, IR absorption, and Raman spectra of these materials are studied. The red luminescence band with a peak at about 700 nm is shown to be due to the radiative transitions in Mn²⁺ ions, which are set in an octahedral oxygen environment. The range of concentration quenching of Mn²⁺ ion radiation is determined. Correlation of the luminescent and vibration properties of these compounds is discussed.     

Optical properties and mechanical characteristics of transparent nanostructured Zn1−xMnxO thin films

Uniform and transparent thin films of Zn_1−xMn_xO (0?x?0.10) were fabricated by a sol-gel spin coating method. XRD results indicated the hexagonal structure of ZnO as the primary phase at all concentrations (x) of Mn. However, at x?0.035, Mn₃O₄ (tetragonal) is observed as the secondary phase, which was confirmed by selected-area electron diffraction patterns. SEM and TEM results showed a tendency of grains to arrange into wire-shaped morphologies, leading to elongated needle-like structures at high Mn addition. Increasing Mn content in the range 0?x?0.10 led to quenching of photoluminescence, increase in the band gap (E_g) from 3.27 to 3.33 eV, and increase in film thickness, refractive index and extinction coefficient of Zn_1−xMn_xO thin films. The residual stress evaluated was compressive in all cases and found to increase by an order of magnitude with addition of Mn. Furthermore, an overall increase in microhardness and yield strength of Zn_1−xMn_xO thin films at higher Mn concentrations is attributed to change in microstructures, presence of secondary phase and increase in film thickness.     

Photoluminescence studies of Cd1−xZnxS nanocrystals

Cd_1−xZn_xS (0?x?0.5) nanocrystals have been synthesized using a simple chemical precipitation method. Morphological and crystallographic analyses have been done using transmission electron microscope (TEM) and X-ray diffraction (XRD). Room temperature energy and time resolved photoluminescence spectra of these synthesized nanophosphors have been studied using xenon lamp spectroflourometer and high peak power, pulsed N₂-laser excitation, respectively. Photoluminescence spectra are composed of broad peaks ranging from green to red region of the visible spectrum. Important optical parameters: excited state lifetime, trap-depth and decay constant values have been calculated from recorded luminescence decay curves. These nanophosphors show typical lifetime shortening and high quantum yield with increasing concentration of Zn.     

Low‐temperature synthesis and Raman scattering of Mn‐doped ZnO nanopowders

Nanocrystalline Mn‐doped zinc oxides Zn_1−xMn_xO (x = 0–0.10) were synthesized by the sol–gel technique at low temperature. The calcination temperature of the as‐prepared powder was found at 350 °C using differential thermal analysis. A thermogravimetric analysis showed that there is a mass loss in the as‐prepared powder till 350 °C and an almost constant mass till 800 °C. The X‐ray diffraction patterns of investigated nanopowders calcined at 350 °C correspond to the hexagonal ZnO structure without any foreign impurities. The average grain size of the nanocrystal that was observed around ∼25–40 nm from transmission electron microscopy matched well with the crystallite size calculated from the line shape of X‐ray diffraction. The chemical bonding structure in Zn_1−xMn_xO nanopowders was examined using X‐ray photoelectron spectroscopy techniques, which indicate substitution of Mn²⁺ ions into Zn²⁺ sites in ZnO lattice. Micro Raman spectroscopy confirmed the insertion of Mn ions in the ZnO host matrix, and similar wurtzite structure of Zn_1−xMn_xO (x < 10%) nanocrystals. Temperature‐dependent Raman spectra of the nanocrystals displayed suppression of luminescence and enhancement in full width at half maximum in pure ZnO nanocrystals with increase in temperature, which suggests an enhancement in particle size at elevated temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Zn1−x Mg x O (0≤x≤0.05) nanowalls grown on catalyst-free sapphire substrates by high-pressure PLD and their photoluminescence properties

We report the growth of Zn_1?x Mg _x O (x=0, 0.02, 0.05 at.%) nanowalls on sapphire substrates without any metal catalysts by a high-pressure pulsed laser deposition (PLD). The influences of the experimental parameters like growth pressure, temperature, and target-substrate distance on the growth of Zn_1?x Mg _x O nanowalls were systemically studied and the growth mechanism was discussed. It was found that large area and uniform Zn_1?x Mg _x O nanowalls with c-orientation can be grown on sapphire substrates when the growth temperature and pressure were 950 °C and 400 Torr at a target-substrate distance of 2 cm. A thin layer assisted vapor-solid (VS) process was proposed for Zn_1?x Mg _x O nanowalls growth. The photoluminescence spectrum shows the bandgap of Zn_1?x Mg _x O nanowall was effectively expanded together with defect-related levels formation in a forbidden gap, which also induced enhancement of visible emission.     

Mn<Superscript>2+</Superscript> 3<Emphasis Type="Italic">d</Emphasis> luminescence kinetics in Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>x</Subscript>Se

Intracenter luminescence (IL) of Mn²⁺ in Zn_1?xMn_xSe (x=0.07, 0.02) was studied under pulsed excitation by the neodymium laser second harmonic. At 4 K, the IL saturation originates from the nonlinearity of the system only at the instant of excitation, the IL decay kinetics after the exciting pulse termination depending only weakly on the pumping level. At 77 K, the decay kinetics in Zn_0.93Mn_0.07Se depends substantially on the pumping level, because the migration of intracenter excitation over the manganese ions initiates up-conversion, which is a slow nonlinear process. As shown by IL decay measurements in Zn_0.98Mn_0.02Se (x=0.02), excitation migration over the Mn²⁺ ions is insignificant even at a high temperature and under strong optical pumping.     

Photoluminescence of ZnMnTe quantum-well structures in a magnetic field

Photoluminescence spectra of strained structures Zn_{1 ? x} Mn _x Te/Zn_{1 ? y} Mg _y Te with magnetic quantum wells and nonmagnetic barriers are studied. The Zeeman splitting of the heavy exciton is found to follow an unusual behavior: both spin components shift down in energy. The heavy-exciton photoluminescence Zeeman components are observed to be inversely distributed in intensity, with the higher energy component being stronger than the lower energy component. The Zeeman splitting of the exciton in a magnetic field is calculated. The data obtained permit refinement of some parameters of the energy spectrum and magnetic properties of these structures.     

Nanomechanical properties inside the scratch grooves of soda–lime–silica glass

Zn_2?2x Mn_2x GeO₄ (x=0, 0.001, 0.01) phosphors were prepared by conventional solid state reaction technique. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), diffuse reflection spectra, photoluminescence (PL), and cathodoluminescence (CL) spectroscopy were utilized to characterize the synthesized phosphors. The Mn²⁺-activated Zn₂GeO₄ phosphors exhibit narrow emission band at 532 nm under the excitation of ultraviolet light, which due to the ⁴T₁(⁴G)–⁶A₁(⁶S) transition of Mn²⁺ ions. Also it is observed that there exists energy transfer between the Zn₂GeO₄ host lattice and the activator (Mn²⁺). Under excitation of low-voltage electron beams, Zn₂GeO₄:Mn²⁺ shows strong green emission band dominating at 535 nm, corresponding to the ⁴T₁(⁴G)–⁶A₁(⁶S) emission of Mn²⁺ ions. The emission intensity and chromaticity coordinates of Zn₂GeO₄:Mn²⁺ as a function of accelerating voltage and the filament current were also investigated.     

Room-temperature ferromagnetism and optical properties of Zn1−xMnxO nanoparticles

The room-temperature ferromagnetism is observed in Zn_0.98Mn_0.02O nanoparticles, which is related to the host-lattice defects induced by doping Mn. The ferromagnetism in Zn_0.95Mn_0.05O nanoparticles can be suppressed by Mn clusters. The additional peak at 519 cm^?1 is observed in Raman scattering spectra of the Zn_1?xMn_xO nanoparticles associated with intrinsic host-lattice defects, which become activated due to the Mn doping. The decrease in band gap and the weak intensity of absorption peak in the nanoparticles may be due to the sp–d interaction between transition metal and Zn anions.     

Structural and photoluminescence analysis of Zn1 − xMnxO nanocrystalline powders

This Letter reports on structural and photoluminescence properties of Zn_1 − xMn_xO nanocrystalline powders, which were synthesized by using oxalate precursor decomposition method. From the XRD features, we have noticed that all samples exhibit wurtzite crystal structure. The origin of photoluminescence properties of Mn doped and undoped ZnO have been discussed.     

Structural,thermal and magnetic investigations of heavily Mn-doped ZnO nanoparticles

We present a systemic study on the structural, thermal and magnetic properties of Zn_1?xMn_xO nanoparticles synthesized by a combustion method with heavily Mn doping concentrations x=0.05, 0.15 and 0.25. The structural evolutions in relation to the possible variation of the Mn oxidation state and dopant induced tiny Zn₂MnO₄/Mn₂O₃ and ZnMnO₃/MnO₂ impurities, which have not been detected by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), were investigated by means of X-ray photoelectron spectroscopy (XPS), Raman scattering spectra, thermo-gravimetric analysis (TGA) and magnetic measurements. It is evidenced that the optimal Mn concentration x in ZnO to grow single phase Zn_1?xMn_xO should be below the cation percolation threshold x_p (about 0.125), which is the basis to form real diluted magnetic semiconductors (DMSs).     

No room temperature ferromagnetism in Mn over-doped Zn1−xMnxO (x>0.02)

Mn-doped ZnO samples having composition Zn_1−xMn_xO (x=0.02, 0.04 and 0.05) were synthesized by solid state reaction technique with varying concentration of Mn from 0.02 to 0.05. Evidence of room temperature ferromagnetism was observed only in the composition Zn_0.98Mn_0.02O sintered at 500 °C. Our XRD pattern confirms the presence of Mn₃O₄ impurity phase in all the Zn_1−xMn_xO samples with the exception of Zn_0.98Mn_0.02O. We emphasize that the appearance of Mn₃O₄ phase in the system forbids the exchange type of interaction between the Mn ions and suppresses the ferromagnetism in all the Mn over-doped Zn_1−xMn_xO (x>0.02) system. SEM microstructure study also supports the interruption of exchange type of interaction inside the system with the increase in Mn concentration in the sample. Interestingly, for this particular composition, Zn_0.98Mn_0.02O sintered at 500 °C, glassy ferromagnetism type of transition is observed at low temperature. This type of transition is attributed to the formation of the oxides of Mn clusters at low temperature.     

Exciton and intracenter radiative recombination in ZnMnTe and CdMnTe quantum wells with optically active manganese ions

The emission spectra of Zn_1?x Mn _x Te/Zn_0.6Mg_0.4Te and Cd_1?x Mn _x Te/Cd_0.5Mg_0.5Te quantum-well structures with different manganese concentrations and quantum-well widths are studied at excitation power densities ranging from 10⁵ to 10⁷ W cm^?2. Under strong optical pumping, intracenter luminescence of Mn²⁺ ions degrades as a result of the interaction of excited managanese ions with high-density excitons. This process is accompanied by a strong broadening of the emission band of quantum-well excitons due to the exciton-exciton interaction and saturation of the exciton ground state. Under pumping at a power density of 10⁵ W cm^?2, stimulated emission of quantum-well excitons arises in CdTe/Cd_0.5Mg_0.5Te. The luminescence kinetics of the quantum-well and barrier excitons is investigated with a high temporal resolution. The effect of the quantum-well width and the managanese concentration on the kinetics and band shape of the Mn²⁺ intracenter luminescence characterized by the contribution of the manganese interface ions is determined.     

BiFeO3/Zn1−xMnxO bilayered thin films

BiFeO₃/Zn_1−xMn_xO (x = 0-0.08) bilayered thin films were deposited on the SrRuO₃/Pt/TiO₂/SiO₂/Si(1 0 0) substrates by radio frequency sputtering. A highly (1 1 0) orientation was induced for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO thin films demonstrate diode-like and resistive hysteresis behavior. A remanent polarization in the range of 2P_r ∼ 121.0-130.6 μC/cm² was measured for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO (x = 0.04) bilayer exhibits a highest M_s value of ∼15.2 emu/cm³, owing to the presence of the magnetic Zn_0.96Mn_0.04O layer with an enhanced M_s value.     

Influence of annealing temperature on structural, optical and magnetic properties of Mn-doped ZnO thin films prepared by sol-gel method

Thin films of Zn_1−xMn_xO (x=0.01) diluted magnetic semiconductor were prepared on Si (1 0 0) substrates by the sol-gel method. The influence of annealing temperature on the structural, optical and magnetic properties was studied by X-ray diffraction (XRD), atom force microscopy (AFM), photoluminescence (PL) and SQUID magnetometer (MPMS, Quantum Design). The XRD spectrum shows that all the films are single crystalline with (0 0 2) preferential orientation along c-axis, indicating there are not any secondary phases. The atomic force microscopy images show the surfaces morphologies change greatly with an increase in annealing temperature. PL spectra reveal that the films marginally shift the near band-edge (NBE) position due to stress. The magnetic measurements of the films using SQUID clearly indicate the room temperature ferromagnetic behavior, and the Curie temperature of the samples is above room temperature. X-ray photoelectron spectroscopy (XPS) patterns suggest that Mn²⁺ ions were successfully incorporated into the lattice position of Zn²⁺ ions in ZnO host. It is also found that the post-annealing treatment can affect the ferromagnetic behavior of the films effectively.     

Structural, chemical and magnetic investigations of polycrystalline Zn1−xMnxO

Present study reports the detailed structural and magnetic, as well as chemical analysis of polycrystalline Zn_1−xMn_xO (where x=0, 0.005, 0.01, 0.03, 0.05 and 0.1) samples synthesized by the high-temperature solid state reaction route. X-ray diffraction studies reveal the presence of secondary phase for higher Mn-doping concentrations (x≥0.03). Secondary phase formation having spinel structure is confirmed and reported as an evidence for the first time using transmission electron microscopy study. Chemical investigations using X-ray photoelectron spectroscopy showed the presence of Mn in two valence states. From the observed results we are of the opinion that Zn²⁺ ions, mainly present at or near grain boundaries, diffuse into manganese oxide to form a stable spinel phase Zn_xMn_3−xO₄ at or near the grain boundaries of ZnO/Zn_1−xMn_xO. Magnetization measurements did not show any magnetic transition down to 5 K.     

Temperature-dependent magnetization in (Mn, N)-codoped ZnO-based diluted magnetic semiconductors

The influences of Mn doping on the structural quality of the Zn_xMn_1−xO:N alloy films have been investigated by XRD. Chemical compositions of the samples (Zn and Mn content) and their valence states were determined by X-ray photoelectron spectrometry (XPS). Hall effect measurements versus temperature for Zn_xMn_1−xO:N samples have been designed and studied in detail. The ferromagnetic transitions happened at different T_C should explain that the magnetic transition in field-cooled magnetization of Zn_1−xMn_xO:N films at low temperature is caused by the strong p-d exchange interactions besides magnetic transition at 46 K resulting from Mn oxide, and that the room temperature ferromagnetic signatures are attributed to the uncompensated spins at the surface of anti-ferromagnetic nano-crystal of Mn-related Zn(Mn)O.     

Effect of NaF on optical and structural properties of CdxZn1−xS nano crystalline films

This work investigates the effect of NaF on optical and structural properties of nano crystalline Cd_xZn_1?xS films. The Cd_xZn_1?xS films are prepared through chemical bath deposition (CBD) technique in aqueous alkaline bath and their subsequent condensation on substrates. The as-obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–VIS absorption spectroscopy. Micro structural features, obtained from XRD analysis confirm the formation of cubic phase of undoped as well as NaF doped Cd_xZn_1?xS nano particles while SEM observations depict non-uniform distribution of grains. These results show the average grain size of pure as well as NaF doped samples to range from 50 to 90 nm. Tauc's plots, extracted from absorption spectra exhibit absorption to be dominating mainly in blue-green region of visible spectrum. The room-temperature photoluminescence (PL) spectra of Cd_xZn_1?xS samples show a peak around 425 nm, which gets blue shifted for doped sample indicating improvement in PL properties on its addition.     

Studying the elemental composition and manganese distribution in Zn1 − x Mn x Te and Zn1 − x Mn x S films using the μ-PIXE and EDAX methods

The methods of proton-induced X-ray emission (μ-PIXE) and energy-dispersive X-ray analysis (EDAX) are used to study the elemental composition and areal distribution of manganese in Zn_{1 ? x} Mn _x Te and Zn_{1 ? x} Mn _x S films. The μ-PIXE technique is implemented using a nuclear scanning microprobe with a proton-beam energy of 1.5 MeV and cross-sectional dimensions of 4 × 4 μm. The semimagnetic solid solution films are obtained under different operating modes of thermal vapor deposition in the quasiclosed volume of a manganese-containing blend.