Room Temperature Photoluminescence Emission Research Articles

Exploring the structural, morphology, optical and magnetic properties of ZnCoxMn(2-x)O4 prepared using hydrothermal method

Here we report the structural and physical property of ZnCoxMn(2-x)O4 (x = 0, 0.1 and 0.2) materials. The hierarchical ZnCoxMn2-xO4 (x = 0, 0.1 and 0.2) have been successfully synthesized by hydrothermal method. The surface of the ZnCoxMn(2-x)O4 varies according to its composition which is investigated. The absorption and band gap of the material were measured by UV-Vis diffuse reflectance spectroscopy (DRS) in the range of 200 – 800 nm. It was observed that the band gap gets decreased from the parent compound. The room temperature photoluminescence emission spectra of ZnCoxMn(2-x)O4 (x = 0,0.1 and 0.2) has been investigated. The magnetic property of material shows an antiferromagnetic nature. Further, X-ray photoelectron spectroscopy analysis confirms the substitution of Co on Mn site.

Europium(III) Ion-Based photoluminescence complexes of Indole-Derivative β-diketone dominated by ancillary ligands

One pot reaction of β-diketone EIFD, EuCl3·6H2O and ancillary ligand yield a sequence of five luminescence β-diketone EIFD europium complexes, including Eu(EIFD)3(H2O)·CH2Cl2 (1), Eu(EIFD)3(DMSO) (2), Eu(EIFD)3(DMF)·CH2Cl2 (3), Eu(EIFD)3(phen)·CH2Cl2 (4) and Eu(EIFD)3(bpy) (5) (EIFD: 1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluorobutane-1,3-dione, phen = 1, 10-phenanthroline, bpy = 2,2′-bipyridine,). The molecular crystals reveal five mononuclear structures with the central Eu(III) ions of seven/eight coordination configuration furnished by three EIFD ligands and ancillary ligands for complexes 1–5. All the five complexes display room-temperature strong characteristic photoluminescence emissions of Eu(III) ions. The coordination environment of Eu(III) ion is a crucial factor in the optical performance of the complex. Herein, the way to introduce of oxygen and nitrogen ancillary ligands plays an important role in characteristic photoluminescence. The luminescence lifetime and quantum yields of the complexes can vary essentially by substituting the solvent molecules with oxygen and nitrogen ligands, leading to a strong luminescence intensity, as observed experimentally.

Intense and stable room-temperature photoluminescence from nanoporous vanadium oxide formed by in-ambient degradation of VI3 crystals

Vanadium oxides have attracted research interest because their optoelectronic properties make them optically active with room-temperature photoluminescence (PL) emission, which, however, is not sufficiently intense for real applications. For this reason, many nanostructured vanadium oxides are currently fabricated through several precursors and different treatments to improve the PL efficiency and enhance the PL intensity. Herein, we propose an alternative and facile route to the fabrication of nanoporous vanadium oxide flakes through the spontaneous in-ambient degradation of layered van der Waals VI3 crystal, which is composed of a mixture of V2O5 and V3O7 phases. The as-grown VI3 crystals and the formed nanostructured vanadium oxide have been thoroughly studied using X-ray diffraction (XRD) and Raman spectroscopy to access the structural properties, X-ray photoemission spectroscopy (XPS) and synchrotron-based XPS to analyze the electronic core levels and valence bands, scanning electron microscopy (SEM) to access the morphology, and PL spectroscopy to grasp the optoelectronic properties. The nanoporous vanadium oxide system reveals an intense room-temperature PL emission in the red light visible range between 1.7 and 2.0 eV (620 and 730 nm), which is consistent with the V2O5 PL response. Remarkably, the PL emission reaches high intensity compared with those of different V2O5 nanostructures and is stable for months without intensity quenching and energy shifting. This discovery easies the integration of nanostructured vanadium oxides in optoelectronic nanodevices. Besides, the facile methodology proposed here promises to be applied to realize other nanostructured transition metal oxides.

Structural and transport properties of Cu2CoSnS4 films prepared by spray pyrolysis

In the present work, stannite Cu2CoSnS4 (CCTS) films were elaborated using spray pyrolysis method on soda-lime glass, at different deposition temperatures (Td = 250, 300, and 350 °C), followed by different chosen sulfurization temperatures (Ts = 450, 500, and 550 °C). X-ray diffraction (XRD) revealed the nearly single-phase formation of CCTS films at 300 °C deposition temperature. After sulfurization in argon flow, the XRD lines become narrower, the average crystallite size expanding above 70 nm. The Raman spectroscopy analysis confirmed the stannite structure formation, as well as the presence CoS2 secondary phases, which reduces at higher sulfurization temperature (550 °C). The energy dispersive spectroscopy results indicated atomic ratios of Cu/Co/Sn/S close to the ideal stoichiometric ratio 2:1:1:4. The room temperature photoluminescence emission is recorded with maximum in the 1.35–1.40 eV range. Thermoelectric properties are measured up to 130 °C, the films show poor power factor as a result of small positive Seebeck coefficients 10–45 μV K−1 and low electrical conductivity despite of having relatively high carrier concentration (∼1020 cm−3).

Role of Na+ co-doping in luminescence enhancement of Bi2O3: Sm3+ nanophosphors

In this paper, we present a comprehensive structural and optical study of alkali metal ion (Na+) co-doping in samarium-doped bismuth oxide nanophosphors and its role in enhancing the red emission of the phosphors. X-ray diffraction (XRD) analysis ascertains the monoclinic crystal structure (space group P21/c) of the synthesized phosphors with crystallite size in the 49–65 nm range. The XRD analysis also reveals an improvement in crystallinity after Na+ co-doping in Sm3+ doped Bi2O3 phosphors. The HR-SEM micrographs reveal the nanosheet-like morphology and the EDX spectroscopy confirms the presence of all elements in the prepared phosphors. The TEM analysis validates the structural and morphological findings. The UV–Vis–NIR spectroscopic analysis has been carried out to estimate the bandgap as well as to investigate the Urbach energy of the phosphors. An augmentation in bandgap energy (2.784–2.807 eV) is observed for lower Na+ co-doping in samarium doped phosphor and shows a decreasing trend with increasing Na+ concentration. FTIR spectroscopy was probed to analyze the chemical bonding, modes of vibration, and detection of functional groups in the samples. The room temperature photoluminescence (PL) emission studies were performed under 481 nm excitation which exhibits an explicit redshift of the CIE coordinates. Nearly ten-fold enhancement in the emission intensity was observed in the optimized Bi2O3:(5%)Sm3+ with co-doping of 1% Na + ions. The lifetime of the 4G5/2 level of the Sm3+ ions has also increased on doping 1% Na+ ions. The thermal stability of the phosphors has been investigated using temperature-dependent PL analysis over the temperature range of 303–453 K. The correlated color temperature (CCT) analysis of the samples reveals that the prepared nanophosphors are promising and potential red-emitting phosphors to realize efficient optoelectronic and display devices.

Influence of Ion Beam Irradiation on Optical and Magnetic Properties of Transparent Mn Doped ZnO Thin Films, Suitable for Sensor Applications

The present work describes modification in physical properties of Zn0.95Mn0.05O films by ion beam irradiation. Films were prepared by spin coating and annealed at 500 °C. XRD patterns of these films show wurzite structure with good crystalline quality. However, Low energy irradiation could modify and induces new defect states. Characterization of those defects had been performed by analysing the UV-Visible absorption spectroscopy and Photoluminescence (PL) spectroscopy. Room temperature PL emission of Zn0.95Mn0.05O film shows a broad UV emission and pronounced visible emission ∼530 nm. At low temperature broad UV band become more prominent however it is completely quenched after irradiation. For all irradiated films we had notice only visible emission of comparable intensities, confined within the region 475 nm to 550 nm. Irradiated films are showing ferromagnetism at room temperature and most importantly the film irradiated at fluence F: 1016 ions cm−2 exhibit maximum saturation magnetic moment of 0.83 emu g−1. The magnetic response is strongly influenced by irradiation and we could say that magnetism is strongly correlated with intrinsic defects present in these films. Defect induced formation of bound magnetic polarons (BMP) actually control the ferromagnetic property of these films. These transparent ferromagnetic films could be used in optoelectronics.

Room temperature optical detection of ultra-low ozone concentration using photoluminescent ZnO nanohybrids

The highly sensitive room temperature (RT) photoluminescence (PL) emission of zinc oxide (ZnO) in the presence of ozone (O3) is demonstrated for the first time. The optical materials examined consist of commercially available luminescent ZnO nanoparticles (ZnO NPs), as well as ZnO/polymer nanohybrids, with different polymeric matrices (poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) and polydimethylsiloxane (PDMS)), which are excited with a UV pulsed laser source (λex= 248 nm, τex= 15 ns).The PL emission of the ZnO NPs and their nanohybrids (ZnO/PPEGMA, ZnO/PDMS) is investigated upon exposure to ozone gas and their sensing characteristics, such as response (%ΔI), reversibility, response/recovery time are determined, as a function of ozone concentration in synthetic air.Sensing tests revealed that all materials allowed the detection of ozone gas in a wide range of concentrations in synthetic air (1600 down to 50 ppb), with the ZnO/PDMS nanohybrid exhibiting the highest response and recovery time of about 50 s (at 750 ppb ozone concentration) and 100 s, respectively. Finally, its remarkable optical response of about 20% at 50 ppb ozone concentration at RT, underlines the great potential of the ZnO/PDMS nanohybrid to serve as a sensitive probe for ozone detection, thereby introducing new developments in optosensing applications.

Structural, morphology and optical properties of PbS (Lead Sulfide) thin film

We report here the synthesis, structural and optical properties of PbS thin film. The growth rate in the chemical path deposition time was optimized during film deposition. The surface of the PbS film is compact and well covered, with a smooth surface and irregularly shaped spherical grain of random sizes. The electrical studies were measure with the Hall effect and Hot probe for the optimized film and the transmittance and band gap of the films were measure by the UV–VIS–NIR Spectrometer in the range of 400–2500 nm. It was observed that the band gap decreases and thickness increased with the increases in deposition time. The room temperature photoluminescence emission spectra of the as grown PbS thin films. Radiation of wavelength 425 nm was used for excitation.

Synthesis, structural, topographical, optical and luminescence of CeO2/SnO2 2D hexagonal nanostructures

Optical properties of 2D nanostructures are widely attracted due to its tremendous applications. In this work, CeO2/SnO2 nanocomposites with 2D hexagonal nanostructures were synthesized by the wet chemical method using mixed solvent water/ethane-1,2-diol. The properties of the CeO2/SnO2 nanocomposites were characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Transmission electron microscopy (TEM), UV-Diffuse Reflectance spectroscopy (UV-DRS) and Photoluminescence (PL) spectroscopy. The TEM images show that the water/ethane-1,2-diol assisted CeO2/SnO2 nanocomposite exhibit formation of uniformly dispersed 2D hexagonal nanostructure. The powder XRD results confirmed the formation of CeO2/SnO2 nanocomposites, further it shows the water/ethane-1,2-diol assisted nanocomposite exhibit low intensity peak which is due to the small particle size. Roomtemperature photoluminescence (RTPL) emission studies indicate that as obtained CeO2/SnO2 2D hexagonal nanostructure have much stronger emission than water/ethanol assisted CeO2/SnO2 nanocomposites. The band gap energies of the samples prepared for water/ethanol and water/ethane-1,2-diol obtained by the tauc plots of (αhυ)2 versus (hυ) curve are 3.21 and 3.22 eV respectively.

Synthesis, luminescent properties, and thermal stabilities of Gd2(1-x)Eu2x(MoyW1-yO4)3 (0≤x≤0.2, 0≤y≤1) solid solution phosphors

Through a solid-state reaction method, Gd2(1-x)Eu2x(MoyW1-yO4)3 (0 ≤ x ≤ 0.2, 0 ≤ y ≤ 1) solid solution phosphors were synthesized. The crystalline structures, the morphologies, and the compositions of the solid solution phosphors were characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscope (FE-SEM) images, energy-dispersive spectra (EDS), respectively. The diffuse reflection spectra (DRS), room temperature photoluminescence (PL) excitation and emission spectra, luminescence decay curves, and high temperature PL spectra were recorded to characterize the luminescent properties, the luminescent dynamics, and the thermal behaviors of the phosphors. The synthetic temperatures were explored to determine the optimal synthetic temperature. The Eu3+ concentration quenching effects were observed in the orthorhombic phase of Gd2(1-x)Eu2x(MoO4)3 phosphors and the monoclinic phase of Gd2(1-x)Eu2x(WO4)3 phosphors. By introducing Mo6+ to Gd2(1-x)Eu2x(MoyW1-yO4)3 phosphors, crystalline phase variations and red shift excitation bands were recorded. Enhancing Eu3+ excitation and emission intensities were recorded in the Gd2(1-x)Eu2x(MoyW1-yO4)3 solid solution phosphors with the concentration of W6+ increasing. The obtained Gd2(1-x)Eu2x(MoyW1-yO4)3 phosphors can be used in phosphor converted based ultraviolet (UV) LEDs.

Room temperature emission from single defects in WO3 enhanced by plasmonic nanocrystals

Room temperature light emission from optically active defect centers in two-dimensional layered materials has attracted great interest in recent years owing to the critical applications in the field of quantum information technologies. Therefore, efficient generation, detection, characterization, and manipulation of spatially localized emission from the defect centers are of crucial importance. Here, we report localized, stable, and bright room temperature photoluminescence (PL) emission from defects in WO3. In particular, the experimentally observed polarized and power dependent PL emission shows single photon characteristics. In addition, density functional theory calculations indicate that the source of the emission is most probably oxygen vacancy defects in WO3. The PL emission obtained from the localized defect centers in WO3 at room temperature has been, further, enhanced more than 20 times by using plasmonic gold nanoparticles.

Kinked silicon nanowires prepared by two-step MACE process: Synthesis strategies and luminescent properties

We report the controlled fabrication of kinked silicon nanowires (SiNWs) using ethanol mixed facile two-step metal-assisted chemical etching (MACE) method. Accordingly, the kink angle, straight path, and the number of kinks in kinked SiNWs are controlled by varying the volume of ethanol and etching time in high concentrated plating and etching solutions. The silver nanoparticles (AgNPs) during the etching need to travel a critical length (≥1.5 μm) in a vertical direction before the kink formation. The presence of ethanol in etching solution affects the availability of H2O2 and HF at Si/Ag interface and has a major effect on the etching process. The room temperature photoluminescence (PL) emission of kinked SiNWs is tuned from the red region to the blue region by controlling the amount of ethanol in the etching solution. The temporal behaviour of the PL data of the kinked SiNWs has been provided to understand in depth the optical transition processes.

Mutual effect of solvent and Fe-In codoping on structural, optical and electronic properties of ZnO thin films prepared by spray pyrolysis technique

This work demonstrates a comparative analysis of structural, morphological, optical and electronic properties of ZnO thin films with respect to change in solvent composition as well as relative codoping concentration of Fe and In. Two different solvent compositions are used i.e. methanol mixed with de-ionized water (methanol-water) and only de-ionized water. X-ray diffraction analysis shows methanol-water solvent resulting preferred orientation along (002) plane. However, de-ionized water derived ZnO samples depicts the usual three most intense peaks along (100), (002) and (101) planes as in case of zincite. There is also observed a change in morphology of the films e.g. flake like nanoparticles are found in 1 at.% Fe and 3at.% In co-doped ZnO thin films synthesized using methanol-water only. Room temperature photoluminescence emission spectra show evolution of a strong emission at 415 nm in case of low doping concentration of Fe (1–3 at.%) in codoped ZnO samples.

Fluorine-based color centers in diamond

We report on the creation and characterization of the luminescence properties of high-purity diamond substrates upon F ion implantation and subsequent thermal annealing. Their room-temperature photoluminescence emission consists of a weak emission line at 558 nm and of intense bands in the 600–750 nm spectral range. Characterization at liquid He temperature reveals the presence of a structured set of lines in the 600–670 nm spectral range. We discuss the dependence of the emission properties of F-related optical centers on different experimental parameters such as the operating temperature and the excitation wavelength. The correlation of the emission intensity with F implantation fluence, and the exclusive observation of the afore-mentioned spectral features in F-implanted and annealed samples provides a strong indication that the observed emission features are related to a stable F-containing defective complex in the diamond lattice.

(Invited) Engineering SiGeSn Semiconductors for MIR and THz Opto-electronic Devices

Sn-containing group IV semiconductors (Si)GeSn represent a versatile platform to implement a variety of Si-compatible photonic, optoelectronic, and photovoltaic devices operating from SWIR to MIR wavelengths. This class of semiconductors provides two degrees of freedom, strain and composition, to tailor the band structure and lattice parameter thus enabling a variety of heterostructures and low-dimensional systems on a Si substrate.[1]In this presentation, the recent progress in the epitaxial growth and opto-electronic properties of metastable (Si)GeSn semiconductors with Sn contents above 15 at.% will be discussed. The growth of the (Si)GeSn multi-layer heterostructure is performed in a chemical vapor deposition (CVD) reactor on a Si wafer. By reducing the growth temperature, the Sn content in the alloy is increased, while preserving a high degree of crystal purity for the heterostructure in the topmost Sn-rich layer. Atom probe tomography (APT) measurements will be discussed to address the abruptness of the interfaces and the compositional profile across the GeSn multi-layer heterostructure.[2-4]By tailoring the strain relaxation in Ge0.83Sn0.17 room-temperature photoluminescence (PL) emission wavelength above 4.0 μm upon is achieved.[2,5] The absence of defect- and impurity-related emission and limited carrier losses into non-radiative recombination channels will be addressed using temperature-dependent PL measurements. Direct band gap absorption will be shown using transmission measurements performed at room-temperature, with energies closely matching the PL data. These observations will be discussed in the light of photocurrent measurements on GeSn photodetectors operating up to ~4.6 μm at room-temperature. The integration of p-i-n heterostructures in GeSn photodetectors will be investigated by correlating structural and opto-electronics properties of the fabricated devices.In addition, strategies to further extend the operational wavelength range of (Si)GeSn devices toward THz wavelengths will be discussed.[1] S. Wirths, et al., Prog. Cryst. Growth Charact. Mater. 62, 1 (2016)[2] S. Assali, et al., Appl. Phys. Lett. 112, 251903 (2018).[3] S. Assali, et al., J. Appl. Phys. 125, 025304 (2019).[4] S. Assali, et al., Appl. Phys. Lett. 114, 251907 (2019)[5] S. Assali, et al., arxiv:2004.13858

Novel rare earth Dy doping impact on physical properties of PbI2 nanostructures synthesized by microwave route for optoelectronics

Dysprosium (Dy) doped lead iodide (PbI2) nanostructures (Dy@PbI2 NSs) were facilely synthesized via microwave-assisted route for the first time and studied by state-of-art experimental tools. Energy dispersive X-ray spectroscopy/scanning electron microscopy (EDX/SEM) elemental-mapping confirm the presence of Dy doping and its standardized dispersal in PbI2 and hexagonal shape nanosheets morphology along with fine nanoparticles was also confirmed. Monophasic hexagonal phase confirmation was carried out using X-ray diffractometry (XRD) and Rietveld refinement, which was further approved via vibrational analysis. The Scherrer rule was employed to determine the size, dislocations and strain in final products and the size was noted between 46 and 53 nm. The energy gap was evaluated for all Dy@PbI2 NSs and noticed to lie between 3.14 and 3.19 eV. Room temperature Photoluminescence emission (RTPLE) was recorded for all Dy@PbI2 NSs at excitation wavelength of 221 nm, which contains one shoulder and three major emission peaks at 455 ± 3 nm, 373 ± 2 nm, 469 ± 2 nm, 528 ± 5 nm. Both quenching and enhancement in PL intensity was observed with Dy doping. Detailed dielectric and electrical analyses were carried out and highest dielectric constant and conductivity was noted for 0.2 wt% Dy@PbI2 NSs. The outcomes indicated that the prepared Dy@PbI2 NSs are good contender for optoelectronics.

Avantium weathers 1H 2020, Catalysis business impacted by pandemic

Dysprosium (Dy) doped lead iodide (PbI2) nanostructures ([email protected]2 NSs) were facilely synthesized via microwave-assisted route for the first time and studied by state-of-art experimental tools. Energy dispersive X-ray spectroscopy/scanning electron microscopy (EDX/SEM) elemental-mapping confirm the presence of Dy doping and its standardized dispersal in PbI2 and hexagonal shape nanosheets morphology along with fine nanoparticles was also confirmed. Monophasic hexagonal phase confirmation was carried out using X-ray diffractometry (XRD) and Rietveld refinement, which was further approved via vibrational analysis. The Scherrer rule was employed to determine the size, dislocations and strain in final products and the size was noted between 46 and 53 nm. The energy gap was evaluated for all [email protected]2 NSs and noticed to lie between 3.14 and 3.19 eV. Room temperature Photoluminescence emission (RTPLE) was recorded for all [email protected]2 NSs at excitation wavelength of 221 nm, which contains one shoulder and three major emission peaks at 455 ± 3 nm, 373 ± 2 nm, 469 ± 2 nm, 528 ± 5 nm. Both quenching and enhancement in PL intensity was observed with Dy doping. Detailed dielectric and electrical analyses were carried out and highest dielectric constant and conductivity was noted for 0.2 wt% [email protected]2 NSs. The outcomes indicated that the prepared [email protected]2 NSs are good contender for optoelectronics.

Spectroscopic and color chromaticity analysis of rhodamine 6G dye-doped PVA polymer composites for color tuning applications

Herein we report the successful fabrication of highly flexible, reversibly stretchable and transparent rhodamine 6G/poly(vinyl alcohol) (Rh6G/PVA) polymer composite (PC) films using a user-friendly solution casting method by adding different amounts, viz. 0, 0.5, 1, 1.5 and 2 wt%, of Rh6G dye. The FTIR studies reveal that an interaction between PVA matrix and added Rh6G dye and room-temperature photoluminescence (RTPL) emission intensity is decreased with the increase in the Tg is observed from DSC thermograms. The developed films show appreciable optical and RTPL properties as established by a UV–visible and fluorescence techniques such that the electronic spectral studies substantiate the changes in electronic band structure of PC films, leading to appreciable changes in the optoelectronic properties. These prepared films with excellent optoelectronic properties alongside appreciable flexibilities and stretchabilities aid their applications to organic light emitting diodes (OLED) with enhanced RTPL studies.

Tunable Shortwave Infrared and Midwave Infrared Optoelectronics in Germanium/Germanium Tin Core/Shell Nanowires

Semiconductor nanowire(NW)-based optoelectronic devices can exhibit superior performances in comparison to their thin film counterparts, as a result of their improved electrical and optical properties. For example, the light-matter interaction in nanowires is enhanced due to the high surface-volume ratio and the light confinement effect resulting from the resonant cavity formed by the nanowire. The enhanced light absorption when using a nanowire geometry can be exploited to increase the responsivity of nanowire-based photodetectors. Light detection and emission at near-IR wavelengths (NIR, 0.8-1.5 μm) can be tailored via strain engineering using Ge-based NW devices.[1] Furthermore, by incorporating Sn in the Ge lattice a direct band gap can be achieved across the short-wave-IR (SWIR, 1.5-3.0 μm) and mid-IR (MIR, 3-8 μm) wavelength range.[2] Despite the equilibrium solubility of Sn in Ge being limited to ~1at.%, non-equilibrium growth methods recently developed in a chemical vapor deposition (CVD) reactor demonstrated a Sn content of 18 at.% with a room-temperature photoluminescence emission up to 4.0 μm [3]. Similarly, when moving to the nanoscale a Sn incorporation well above 10 at.% with a direct band gap emission was demonstrated using Ge/GeSn core/shell NWs.[4]In this presentation, we will discuss the opto-electronic properties of Ge and Ge/GeSn core/shell NWs grown in a CVD reactor using a Ge or Si (111) substrate. The structural properties of the NWs were evaluated by combining Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) in order to understand the nanowire growth direction, crystalline properties as well as Sn distribution uniformity in the shell of the nanowires. Photoluminescence, absorption and Raman measurements will elucidate the effect of strain on the MIR direct bandgap emission/absorption of the GeSn shell.Finally, wewill discuss the electrical characterization of individual Ge and GeSn NW photodetectors. Our devices are fabricated by Electro-Beam Photolithography (EBL) based on metal-semiconductor-metal (M-S-M) structure to address the dependence of the photocurrent under illumination at different SWIR-MIR wavelengths. The time response and transport properties of Ge and Ge/GeSn core/shell NW Field Effect Transistor (FET) in back-gated structure are compared with their counterparts of conventional thin film heterostructures. References Pilon, FT Armand, et al. "Lasing in strained germanium microbridges." Nature communications1 (2019): 1-8.Assali, S., J. Nicolas, and O. Moutanabbir. "Enhanced Sn incorporation in GeSn epitaxial semiconductors via strain relaxation." Journal of Applied Physics2 (2019): 025304.Assali, S., et al. "Atomically uniform Sn-rich GeSn semiconductors with 3.0–3.5 μ m room-temperature optical emission." Applied Physics Letters25 (2018): 251903.Assali, S., et al. "Growth and optical properties of direct band gap Ge/Ge0. 87Sn0. 13 core/shell nanowire arrays." Nano letters3 (2017): 1538-1544.

Structural, Raman and photoluminescence studies on nanocrystalline diamond films: Effects of ammonia in feedstock

Herein, we report on the improvement of structural quality and enhancement of photoluminescence (PL) emission for an optimally N doped nanocrystalline diamond (NCD) film. Pure and N doped nanocrystalline diamond films are synthesized on Si by hot filament chemical vapour deposition using NH3:CH4:H2 at different nominal N/C ratios viz. 0, 0.13, 0.35, 0.50 and 0.75 in feedstock. X-ray diffraction analysis reveal a systematic initial increase and then a decrease in crystallite size with N/C ratio in feedstock. Further, a monotonic increase in Raman line width and peak position of diamond band indicates that the compressive strain in diamond lattice increases as a function of N/C ratio upto 0.50. However, at higher N/C ratio of 0.75, the compressive strain gets relaxed a little and produces a lower strain. Furthermore, a unique Raman mode at 1195 cm−1 is observed corresponding to the C=N-H vibrations indicating a significant N concentration in the NCD films. In addition, visible and UV PL studies reveal the presence of several N-related color centres with multiple emission lines in the range of 380–700 nm. An optimally N doped diamond film grown at N/C ratio of 0.35 in feedstock shows a significant enhancement in room temperature PL emission at ~505 and 700 nm. This PL enhancement is attributed to H3 and other aggregates of N related defect centres, under 355 and 532 nm laser excitations, respectively.