Band Edge Emission Research Articles

Characteristics of aluminium nitride thin film prepared by pulse laser deposition with varying laser pulses

In this work, the studies of Aluminium Nitride (AlN) thin film deposited on silicon (Si) (111) substrate using the pulsed laser deposition (PLD) method, specifically under different number of laser pulses, were performed. From the electron micrographs, the samples exhibited a densely packed granular morphology. The film thickness, particle size, and surface roughness were found to be increasing along with number of laser pulses. X-ray diffraction analysis revealed all AlN samples to have hexagonal wurtzite structure. Additionally, the calculated lattice constants suggest AlN experiences inward biaxial stress during growth. This was in agreement with the Raman results, aside from substantiating the presence of AlN with (100) and (101) plane to be grown. Room temperature photoluminescence (PL) measurements showed band-edge emission was attributed to AlN along with some defect-related bands. Additionally, the band-edge emission shifted to higher photon energy, i.e. 5.49–5.89 eV with increasing laser pulses. Such observations were consistent with that obtained from UV–Vis spectroscopy.

Investigation on spontaneous recombination mechanisms in GaN based laser diodes under low injection current

This study works on the spontaneous recombination mechanisms of GaN-based laser diodes (LDs) under low injection current by examining their power–current (P–I) curves and electroluminescence spectra. Our investigation focuses on the behavior of differential efficiency in LDs under low injection current, revealing that a competition between impurity-related yellow emissions and band-edge blue emissions leads to a change in total luminescence efficiency. Using both experimental and simulating methods, the yellow emission peak is primarily attributed to carrier recombination in deep-level defects located on the LD's p-side. A detailed explanation to the differential efficiency changing mechanism is beneficial to improve the GaN-based LD performance in future fabrication.

Investigation of carrier transport and recombination at type-II band aligned p-NiO/AlGaN interface in p-NiO gate AlGaN/GaN HEMTs under forward bias

In this work, fine carrier transport and recombination processes in p-NiO gate AlGaN/GaN high electron mobility transistors were investigated by analyzing their electroluminescence under forward gate bias, with photoluminescence spectrum as a reference. Red luminescence with a peak of 1.9 eV was captured when the gate bias voltage exceeded 4 V, which was verified to originate from the tunneling enhanced interface recombination of injected holes from the gate metal and spilled electrons from the 2DEG channel at the type-II band aligned p-NiO/AlGaN heterostructure interface. Under higher gate bias voltage, holes were further injected into the GaN buffer layer, producing ultraviolet luminescence and yellow luminescence, corresponding respectively to the band edge emission and defect-assisted radiative recombination of GaN. Threshold voltage shift measurements under forward gate bias were conducted to further investigate the carrier transport and recombination processes.

The effects of nontoxic bio-based substances (egg white) on the performance and passivation of ZnO nanorods arrays-based light emitting devices

An innovative approach is proposed to passivate the existing defects from metal oxide semiconductors by functionalizing nontoxic bio-based substances. As a demonstration, we synthesized zinc oxide nanorods (ZnO NRs) using a hydrothermal method and incorporated chicken egg white (albumen) as a passivator to the defects. X-ray diffraction analysis of ZnO NRs shows enhanced quality and crystallinity features after incorporating albumen. XPS measurements were performed not only to introduce the chemical bonding between the albumen and the bare ZnO NRs but also specifically provide evidence of successful capping and defect passivation to the surface layer of ZnO NRs. It was observed that when the albumen was annealed, it formed sulfhydryl groups and disulfide bonds (which created disulfide bridges) from the chemical reaction in irreversible thermal denaturation. Steady-state photoluminescence of ZnO NRs showed two emission bands, i.e. near band-edge emission (NBE) and deep-level emission (DL). The NBE is significantly improved as compared to DL emission after capping and annealing the albumen, while the quenching of DL emission confirmed the reduced defects arising from the surface of ZnO NRs. The advantages and enhanced characteristics of the albumen-capped ZnO NRs led to fabricating a stable and highly efficient light-emitting device. This work opens the great potential of utilizing nontoxic and low-cost biomaterials in passivating the defects of metal oxide nanomaterials for the development of bio-inspired and stable optoelectronic devices.

Surface optical phonon replica in photoluminescence spectroscopy of nitride nanostructures: Crystal structure and surface effects

The surface optical (SO) phonon replica in photoluminescence (PL) spectroscopy of nitride nanowires (NWs) was theoretically investigated in this study. The dispersive relationships of SO phonon mode in anisotropic wurtzite (WZ) and isotropic zinc-blende (ZB) crystal structure NWs with circular and square cross sections (CSs) were derived within the framework of the dielectric continuum model. Based on the energy and momentum conservation laws, a constraint relationship between the frequency and wave-number was constructed for SO phonon-assisted excitonic PL spectra in the NW structure. By combining the dispersive and constraint relationships, the frequency and wave-number of the SO phonon replica in the PL spectra could be determined. The WZ and ZB crystal structures of nitride semiconductor were considered. The influences of surface factors including the CS shape, dielectric medium, and environment temperature on the frequency and photon wavelength of the band-edge emission of the SO phonon replica were studied in detail. Numerical results reveal that the crystal structure, surface factors, and environment temperature greatly affect the frequency and photon wavelength of the band-edge emission of the SO phonon replica. The calculated results for the photon wavelength agree well with the experimental values of the SO phonon replica in AlN NWs. The results of the dielectric effect obtained here are also supported by previous experimental and theoretical results for nitrides and other semiconductor NWs. The present theoretical scheme and numerical results can be used to analyze and design the SO phonon replica in PL spectra of nanostructures.

Low temperature dielectric study and photoconductive analysis of ZnO/NiO composite material

The sol-gel process was used to synthesize a ZnO–NiO composite material in this study. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the material, which confirmed the existence of both ZnO nanoparticles and NiO sheets in the composite. The composite material contained two distinct crystalline phases, the face-centered cubic phase of NiO and the hexagonal phase of ZnO. The composite's average crystallite size was determined to be 19.0 nm. The particle size of the composite material was calculated to be ∼121 nm. The band edge emission at 393 nm (3.15 eV) was measured using photoluminescence (PL) spectroscopy. The PL spectrum revealed other emissions as well. The dielectric properties of the material were studied at low temperatures in the frequency range of 20 Hz to 1 MHz, and it was found to have a low dielectric dissipation at high frequencies, making it suitable for use in high frequency microwave devices. Impedance data was fitted using Z-View software with a fitting error of <5%. Impedance spectroscopy revealed that the composite material had two dielectric relaxation processes related to the bulk and the grain boundary. Analysis of frequency dependent ac conductivity revealed Overlapping large-polaron hopping (OLPH) is responsible conduction mechanism in our case indicated by variation of temperature (200–280 K) dependent parameter “s” with temperature. Photoconductivity studies showed that the composite material had enhanced electrical conductivity and photoconductivity compared to pure ZnO and NiO. This makes it a promising candidate for use in optoelectronic applications such as solar cells, optical switches, and photodetectors. The responsivity of composite (0.86 mA/Watt) is found to be 10 times greater than that of the responsivity of NiO (0.085 mA/Watt).

Resonant Multiple-Phonon Absorption Causes Efficient Anti-Stokes Photoluminescence in CsPbBr3 Nanocrystals.

Lead halide perovskite nanocrystals, such as CsPbBr3, exhibit efficient photoluminescence (PL) up-conversion, also referred to as anti-Stokes photoluminescence (ASPL). This is a phenomenon where irradiating nanocrystals up to 100 meV below gap results in higher energy band edge emission. Most surprising is that ASPL efficiencies approach unity and involve single-photon interactions with multiple phonons. This is unexpected given the statistically disfavored nature of multiple-phonon absorption. Here, we report and rationalize near-unity anti-Stokes photoluminescence efficiencies in CsPbBr3 nanocrystals and attribute them to resonant multiple-phonon absorption by polarons. The theory explains paradoxically large efficiencies for intrinsically disfavored, multiple-phonon-assisted ASPL in nanocrystals. Moreover, the developed microscopic mechanism has immediate and important implications for applications of ASPL toward condensed phase optical refrigeration.

Crystal growth, optical, photoluminescence and magnetic properties of sol-gel GdFeO3 thin film

GdFeO3 (GFO) orthoferrite is a perovskite structured material with rich physical properties. In this work, crystal growth, electronic, optical, photoluminescence (PL) and magnetic properties of sol-gel synthesized GFO thin films onto quartz substrate were investigated. The films were annealed at various temperature 650–900 °C. XRD results showed transformation from an amorphous to nanocrystalline GFO and GdO secondary phase with rise of annealing temperature from 650 to 700 °C. Single phase GFO was observed in films annealed above 700 °C. Crystallite size of the films gradually increased from 10.5 to 89.9 nm for films annealed from 700 to 900 °C, respectively. The surface morphology changed from porous microstructure consisted of tiny particulates in film annealed at 700 °C into enlarged particles and clear polycrystalline structure in films annealed above 700 °C. From XPS spectra analysis, both Fe and Gd ions existed in a 3+ valence state. The films demonstrated optical band gap ranged between 2.8 and 3 eV. The PL spectra obtained using a 300 nm excitation wavelength consisted of four emission peaks. The near band edge emission of the films varied between 449.9 and 455.1 nm. The films showed weak ferromagnetic behavior with magnetization ranging from 24 to 49 emu/cm3.

Photo-induced luminescence mechanism and the correlated defects characteristics in the sol-gel derived samarium ion substituted tin oxide (Sn1-xSmxO2) nanoparticles

Rare earth complexes have gained attention in recent years for their remarkable luminescence properties, especially their long lifetimes, clear emission bands, and significant luminous quantum efficiency. In the ultraviolet area, the lanthanide ions exhibit relatively tiny absorption. The current investigation systematically portrays the tailoring of the micro-structural, opto-electonic and defect related features of the sol-gel derived pristine and rare earth element-samarium (Sm3+) substituted tin oxide (SnO2) i.e., Sn1-xSmxO2 (x = 0.0, 0.1, 0.2 & 0.3) nanoparticles (NPs). The structural, optical, electronic, morphological, photo-induced luminescence and defects related characteristics of the NPs were explored as a function of samarium (Sm3+) substitution level. In-depth analysis of the structure-property correlation of the Sn1-xSmxO2 NPs is the goal of this study, focusing especially on the properties related to vacancy evolution and luminescence. The elemental mapping results revealed through energy dispersive X-ray spectroscopic (EDS) technique confirmed that the Sm-substitution is distributed uniformly throughout the NPs. The X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) studies corroborate that the Sm3+ substitution in the SnO2 matrix causes the decrease in crystallite size of the NPs and increase in the dislocation density. A monotonic increase in lattice strain has been observed using the Williamson – Hall (W – H) approach, which is in line with the NPs' increased dislocation density and decreased crystallite size with the Sm3+ substitution level. The presence of vacancy-type defects inside the NPs was demonstrated by positron annihilation lifetime (PAL) spectroscopic measurements, and a decrease in defects was noticed as the level of Sm3+ substitution increased. To explore the optical characteristics and the evolution of the energy band gap with Sm3+ substitution level, the optical absorption (OA) spectroscopic measurement was carried out. As the Sm-substitution level rises, the optical energy band gap of the substituted SnO2 NPs widens relative to that of pure SnO2 NPs. The existence of various absorbance bands corresponding to the atomic vibrations within the NPs were investigated by the Fourier-transform infrared (FT-IR) spectroscopic technique. The photo-induced fluorescence (FL) emission spectroscopic analysis evidenced that the defect density decreased as the Sm-substitution level increased, which is in accordance with the PAL spectroscopic studies. The FL spectra showed the two typical near band edge (NBE) and deep level emission (DLE) peaks of the NPs. The proportion of different defects and vacancies associated with the FL emission transitions are portrayed as Pie-chart diagrams. The tailored NPs can establish to be effective candidates for possible spintronic and optoelectronic applications including magneto-optical devices.

Employing zinc oxide nanoparticle coating as a corrosion inhibitor for magnesium alloys in distinct aqueous electrolyte

In this investigation, zinc oxide nanoparticles were synthesised using a straightforward microwave-assisted technique. Results showed that the synthesised nanoparticles were hexagonal wurtzite ZnO-nanoparticles with a crystallite size of 6.76 nm, as determined by physio-chemical methods. It reveals, at varying magnifications, the irregularly aggregated, spherically shaped sponge-like structure. Using Fourier transform infrared spectroscopy, corresponding functional groups on ZnO surfaces have been observed. According to absorption measurements, the direct optical bandgap is around 3.29 eV. The photoluminescence spectra may be used to detect crystal defects in the ZnO lattice by looking for red emission and blue band edge emission. An investigation into the anticorrosion capabilities of zinc oxide nanoparticles was conducted, which revealed that the particles have beneficial characteristics when coated with magnesium (Mg) substrates. These materials are evaluated for corrosive resistance with and without a protective coating. Results show that coating significantly increased the protection rate under different electrolyte conditions. Compared to bare Mg plate, the charge transfer resistance Rct was increased when ZnO nanoparticles were coated.&#x0D; KEY WORDS: Zinc oxide nanoparticle, Microwave irradiation, Corrosion resistance, magnesium alloy&#x0D; Bull. Chem. Soc. Ethiop. 2024, 38(2), 417-430. &#x0D; DOI: https://dx.doi.org/10.4314/bcse.v38i2.10

Temperature Dependent Photoluminescence Spectra of Nanocrystalline Zinc Oxide: Effect of processing condition on the excitonic and defect mediated emissions

Nanocrystalline zinc oxide (ZnO) with crystallite size in the range 85 -89 nm are prepared by the thermal decomposition of carbonate precursor under three different atmospheres, viz., in air ambiance, under nitrogen flow, and in vacuum. O 1s X-ray photoelectron spectra indicate that the atomic percentage of oxygen vacancies is more in the sample prepared under vacuum while adsorbed oxygen is more in the sample prepared in air ambience. Optical band gaps for the samples are in the range 3.17–3.20 eV. Room temperature photoluminescence spectra of the samples reveal band edge emission in the UV range (⁓3.18 eV) and broad defect mediated visible emission (⁓1.60–2.70 eV). Emission profile of excitonic emission at 80 K can be resolved into two free excitonic peaks at 3.42 eV (FX-A) and 3.46 eV (FX-B), donor bound excitonic peaks (D0X), peak due to transition of free electrons to acceptor levels (FA) donor-acceptor pair (DAP) emission and phonon replicas. D0X peak at ⁓3.35 eV has contribution from oxygen vacancies (Vo) and Zn interstitials (Zni). The most intense peak in the case of all the three samples is the FA peak at ⁓ 3.31 eV which has contribution from zinc vacancies (VZn). Temperature dependent variation of the dominant D0X and FA peaks in the range 80–400 K are analyzed using modified Varshni model which considers contributions from electron-phonon scattering and lattice thermal expansion. Defect dependent emission intensity is maximum at 80 K due to freeze-out of phonons and decreases with increase in temperature. The evolution of the colour of luminescence with temperature is studied using CIE plot method.

Observation of excellent photocatalytic and antibacterial activity of Ag doped ZnO nanoparticles.

Nanotechnology is the platform with the greatest promise for scientific advancements. One of the advancement is improvement in photocatalytic and antibacterial performance. This work was undertaken to synthesize un-doped and silver (Ag) doped zinc oxide (ZnO) nanoparticles (NPs) using an inexpensive wet chemical method and to investigate the structural and optical properties, photocatalytic and antibacterial activity. The structural analysis from X-ray diffraction (XRD) pattern of un-doped and Ag-doped ZnO NPs displayed hexagonal wurtzite crystal structure and shifting in the peak position confirms the incorporation of Ag in ZnO lattice. Morphological study done by scanning electron microscope reveals spherical shaped NPs and an increase in grain size with Ag doping, the HRTEM images showed the nanocrystalline nature of particle. The Raman spectra showed variation in vibrational characteristics of the nanoparticles with Ag doping. The functional groups were analyzed using Fourier transform-infrared spectroscopy (FTIR). The optical properties were investigated by UV-visible and photoluminescence (PL) spectroscopic techniques. The Ag-doped ZnO NPs have a notably lower band gap than that of un-doped ZnO NPs, i.e. from 3.04 eV to 2.81 eV as studied by UV-visible spectra. The PL study showed decrease in intensity at near band edge emission with increase in Ag doping concentration indicating reduction in the free charge carrier recombination. These variations in the properties play major role in the enhancement of photocatalytic and antibacterial activity with increase in Ag doping concentration as compared to un-doped zinc oxide nanoparticles. The photo degradation efficiency of 99.12 ± 1% against Methylene Blue dye was achieved in the shortest period of 45 minutes ever reported when irradiated under the solar light and efficiency of 97.33 ± 1% was achieved in 15 min under Xenon Short Arc lamp. The antibacterial study was conducted using the Agar well diffusion method where the diameter of the zone of inhibition (ZOI) was increased from 14 mm to 20 mm and 13 mm to 18 mm against the bacteria Escherchia coli and Bacillus subtilis respectively, rendering this material suitable for photocatalytic degradation and antibacterial applications.

Reactivity-matched synthesis of monodisperse Ag(In,Ga)S2 QDs with efficient luminescence.

I-III-VI quantum dots (QDs) have gained widespread attention owing to their significant advantages of non-toxicity, large structural tolerance, and efficient photoluminescence potential. However, the disbalance of reactivity between the elements will result in undesired products and compromised optical properties. Reducing the activity of highly reactive group IB elements is the most common approach, but it will reduce the overall reactivity and lead to a wide dispersion of QD sizes. In this study, we propose a method to improve the overall reactivity of the reaction system using the highly active IIIA precursor InI3, which triggers rapid nucleation and promotes the formation of Ag(In,Ga)S2 (AIGS) QDs, resulting in monodisperse particle size distributions and a significantly improved photoluminescence quantum yield (PLQY) (from 12% to 72%). Furthermore, narrow band edge emission is realized by coating a gallium sulfide (GaSx) shell on the basis of obtaining high-quality AIGS QDs. The core/shell QDs exhibit a 90% PLQY with a full width at half maximum (FWHM) of only 31 nm at 530 nm. This study provides a viable design strategy to synthesize monodisperse AIGS QDs with a narrow peak width and efficient luminescence, promoting the application of AIGS QDs in the field of luminescent displays.

Heterostructure seed-mediated synthesis of zinc phosphide quantum dots for bright band-edge emission.

This study explores the synthesis of colloidal zinc phosphide quantum dots (QDs) by a novel In(Zn)P cluster seed-mediated approach, addressing the challenge of achieving low-cost, high-quality, nontoxic QDs suitable for optoelectronic applications. By intentionally limiting the amount of In precursor added to a hot solvent containing Zn and P precursors, In-rich In(Zn)P cluster seeds were formed. Subsequently, these clusters served as seeds for the growth of zinc phosphide nanocrystals, effectively using the remaining Zn and P precursors for further crystal growth. The synthesized QDs exhibited a tetragonal-like Zn3P2 structure and exceptional optical properties, including band-edge photoluminescence (PL) emission under ambient conditions. A ZnS shell was applied to further enhance the PL intensity, achieving a PL quantum yield of 40% and an average PL decay lifetime of 74 ns, while significantly improving the stability of the QDs. Temperature-dependent PL spectroscopy revealed significant resistance to thermal quenching with an exciton dissociation energy of 62 meV, underscoring the potential of this approach for advancing the field of optoelectronics. This method provides a pathway to fabricate zinc phosphide-based QDs with controlled optical properties and highlights the effective use of earth-abundant materials in the development of environmentally benign photonic materials.

Leveraging plasmonic hot electrons to quench defect emission in metal-semiconductor nanostructured hybrids.

Modeling light-matter interactions in hybrid plasmonic materials is vital to their widening relevance from optoelectronics to photocatalysis. Here, we explore photoluminescence (PL) from ZnO nanorods (ZNRs) embedded with gold nanoparticles (Au NPs). A progressive increase in Au NP concentration introduces significant structural disorder and defects in ZNRs, which paradoxically quenches defect related visible PL while intensifying the near band edge (NBE) emission. Under UV excitation, the simulated semi-classical model realizes PL from ZnO with sub-bandgap defect states, eliciting visible emissions that are absorbed by Au NPs to generate a non-equilibrium hot carrier distribution. The photo-stimulated hot carriers, transferred to ZnO, substantially modify its steady-state luminescence, reducing NBE emission lifetime and altering the abundance of ionized defect states, finally reducing visible emission. The simulations show that the change in the interfacial band bending at the Au-ZnO interface under optical illumination facilitates charge transfer between the components. This work provides a general foundation to observe and model the hot carrier dynamics and strong light-matter interactions in hybrid plasmonic systems.

Impact of Surface Trap States on Electron and Energy Transfer in CdSe Quantum Dots Studied by Femtosecond Transient Absorption Spectroscopy.

The presence of surface trap states (STSs) is one of the key factors to affect the electronic and optical properties of quantum dots (QDs), however, the exact mechanism of how STSs influence QDs remains unclear. Herein, we demonstrated the impact of STSs on electron transfer in CdSe QDs and triplet-triplet energy transfer (TTET) from CdSe to surface acceptor using femtosecond transient absorption spectroscopy. Three types of colloidal CdSe QDs, each containing various degrees of STSs as evidenced by photoluminescence and X-ray photoelectron spectroscopy, were employed. Time-resolved emission and transient absorption spectra revealed that STSs can suppress band-edge emission effectively, resulting in a remarkable decrease in the lifetime of photoelectrons in QDs from 17.1 ns to 4.9 ns. Moreover, the investigation of TTET process revealed that STSs can suppress the generation of triplet exciton and effectively inhibit band-edge emission, leading to a significant decrease in TTET from CdSe QDs to the surface acceptor. This work presented evidence for STSs influence in shaping the optoelectronic properties of QDs, making it a valuable point of reference for understanding and manipulating STSs in diverse QDs-based optoelectronic applications involving electron and energy transfer.

(Invited) Growth of Hexagonal Boron Nitride by MOCVD for Electronic and Photonic Applications

Hexagonal boron nitride (h-BN) is a 2-dimensional (2D) layered insulating material. Thanks to its wide bandgap of ~6 eV and high thermal conductivity, h-BN has been widely utilized as an ideal substrate, gate dielectric material, passivation layer, and atomic tunnelling layer for 2D electronic devices. Recently, it has gained more attention as active material for photonics applications due to its potential for stable quantum emitters in the visible spectral range, as well as deep-ultraviolet emitters and detectors due to its exceptionally high internal quantum efficiency despite its indirect bandgap. However, mechanically exfoliated bulk h-BN and h-BN films grown on catalytic metal substrates by conventional chemical vapor deposition (CVD) systems have been mainly used to study the fundamental properties, lacking in scalability for practical implementation of h-BN.Here, we exploit the scalable approach to grow h-BN on various substrates such as sapphire, Si, and GaN, by using metal-organic chemical vapor deposition (MOCVD). A few-layer h-BN films were successfully grown on those substrates. In particular, we successfully accomplished the conformal growth of few-layer h-BN over an array of Si-based nanotrenches with 45 nm pitch and the aspect ratio of ~ 7:1. Moreover, it was found that at a specific MOCVD growth condition, a very unique h-BN film can be grown on GaN substrates, in which few-layer h-BN film is suspended on GaN nanoneedles. The combination of state-of-the-art microscopic and spectroscopic analyses revealed that the suspended h-BN films exhibit unprecedented deep ultraviolet photoluminescence spectra with local variation in band-edge emission. In addition, the h-BN films show unprecedented atomic stacking configuration, the mechanism of which will be discussed with optical and structural characterizations and theoretical calculations.

Dual effect to improve the electrical properties of SZO films grown by nitrogen pneumatic spray pyrolysis.

The principal aim of this study is to reduce considerably, via Sn doping, the resistivity of ZnO thin films prepared by simple, flexible, and cost-effective nitrogen pneumatic spray pyrolysis (NPSP) method on glass substrates at a temperature of 400°C. Different Sn content was tested (Sn/Zn = 0, 1, 3, 5 wt%) in an attempt to reduce the concentration of excessive oxygen atoms and create more free electrons. The microstructural, optical, morphological, and electrical properties of the films have been studied. The x-ray diffraction analysis demonstrated that tin-doped SZO films exhibited polycrystalline nature with a preferential orientation along (002) plane with the appearance of a new orientation (101) with the increase of Sn concentration leading then to bidirectional growth. The deposited SZO films showed an average optical transmittance of about 80% in the UV-visible region (200-800 nm) with optical band gap values at around 3.27 eV. Photoluminescence emissions of SZO samples presented three main peaks: near band edge emission, violet emission, and the blue-green emission. The surface morphology of the films obtained by scanning electron microscope (SEM) exhibited the change in morphology with increasing the Sn content. A minimum electrical resistivity value of about 17·10-3 Ω·cm was obtained for 3% SZO films. SZO films prepared by the NPSP method can be used as transparent window layer and electrodes in solar cells. RESEARCH HIGHLIGHTS: Highly oriented, conducting, and transparent Sn-doped ZnO films are successfully synthesized. The film growth orientation changed from mono-directional (002) axis to bi-directional (002) and (101) axis according to Sn doping. Ultraviolet and green emissions are noted by photoluminescence investigation. A minimum resistivity is observed for 3 wt% SZO film. The dual positive effect of the carrier gas used (N2) and Sn doping is confirmed.

High-temperature photoluminescence properties of various defects in hydrothermally grown ZnO microrods

High-temperature photoluminescence properties of hydrothermally grown ZnO microrods were reported. Photoluminescence spectra of ZnO microrods deconvoluted into three Gaussian components: near band edge (NBE) emission, Violet emission (VL) and Yellow emission (YL) peaks corresponding to free excitons, zinc vacancies and interstitial oxygen atoms, respectively. Increasing the temperature caused a redshift of the energy position of the NBE and VL peaks and a blueshift of the energy position of the YL peak were observed. In the temperature range from 300K to 473K, the intensities of the NBE and VL bands varied based on a nonlinear pattern. Intensity of these emission bands decreases from temperature 473K–673K. As the temperature increases, changes in the energy and crystal structures of the material due to decrease in the concentration of defects cause a blueshift of the emission bands related to interstitial atoms, and a redshift of the emission bands related to vacancies.

Multifaceted investigations of co-precipitated Ni-doped ZnO nanoparticles: Systematic study on structural integrity, optical interplay and photocatalytic performances

The present study demonstrates the successful synthesis of ZnO and nickel doped ZnO NPs by co-precipitation method. XRD analysis, confirms hexagonal wurtzite structure. The crystallite size increased from 31 to 45 nm with increasing Ni ions and a reduction in the unit cell volume, owing to the smaller ionic radius of Ni2+ compared to Zn2+. PL spectra were observed for pristine ZnO, associated with near band edge emission band, arising from the recombination of free excitons. Due to the splitting of orbitals caused by the presence of magnetic ions, the optical bandgap is found to be decreasing whereas an increase in the occupancy of 3d electrons. The absorption band observed corresponds to the stretching mode below 450 cm−1. A distinctive peak at around 436 cm−1 was identified in the Raman spectra, indicating the high-frequency branch E2 mode in ZnO. Ni-doped (Zn0·91Ni0·09O) NPs achieve about 80 % photodegradation of MEG dye.