Photoluminescence Emission Studies Research Articles

Enhanced dielectrics, ferroelectric and optical properties of lithium niobate for high temperature applications using potassium oxide (K2O) additive

Dielectrics, Ferroelectric and Optical properties of Lithium Niobate has been examined using Potassium Oxide (K2O) as an additive on the samples prepared by solid state reaction method using high energy ball milling. The crystal structure analysis by Rietveld structure refinement confirms that the LiNbO3 (LN) with K2O additive also exhibit the rhombohedral structure with R3c space group. The SEM characterization of the microstructure reveals that the samples sintered at a temperature of 1050 °C, have regular and uniform grain morphology and better density. The average grain size decreases for the K2O added compositions in the beginning and increases later for higher concentration of additive. Thermal study with TGA suggests that as the activation energy is decreases, the polarization is enhanced and the LN composition with 2.72 wt% K2O additive shows the best thermal stability. The frequency and temperature dependent dielectric properties were investigated in a wide range of frequency and a substantial enhancement in the dielectric constant of LN is obtained by K2O addition. A useful enhancement in permittivity is obtained with increase of temperature. The band gap values for direct and indirect band gaps for the various compositions are also determined. The least direct band gap is discovered to be 2.36 eV for the composition with 2.72 wt% K2O additive. The composition-dependent photoluminescence (PL) emission studies reveal that the emission spectra for both the pure LiNbO3 and K2O added LiNbO3 compositions lies in the UV–visible region. All the investigated compositions exhibit distinct green, yellow, and red emission peaks. The LN with 2.72 wt% K2O additive shows the best dielectric, thermal stability and polarization response with maximum polarization Ps ∼1.16 μC/cm2. The present investigations suggest that properties of LN can be significantly improved by using K2O additive for sustainable, low cost, environmental friendly energy storage material for high temperature applications.

Growth, characterization, and anti-bacterial activity of l-methionine supplemented with sulphamic acid single crystals

Abstract Sulphamic acid (SA) crystals supplemented with l-methionine (LM) were grown at moderate temperatures using a slow evaporation procedure. The powder XRD pattern showed that LM supplemented with SA (LMSA) crystals have an orthorhombic crystal structure. The FTIR studies confirmed the presence of various vibrational modes. Using a UV-Vis spectrometer, the transmittance of LMSA in the UV and visible range was observed, and the band gap of the LMSA was also calculated. The hardness value of LMSA was higher compared to that of pure SA. Photoluminescence emission studies of LMSA pointed out emissions at 491 and 542 nm, which were attributed to the transition from the 5D4 state to 7F6 and 7F5 ground, respectively. LMSA crystals were effective in killing pathogenic bacteria, according to the studies on their anti-bacterial activity.

Luminescence properties and energy transfer studies in thermally stable Bi2O3: Sm3+, Eu3+ phosphor

The advent of innovative rare-earth based metal oxide phosphors has prompted increasing interest in the search for highly efficient red emitting phosphors for various optoelectronic devices, lighting and display applications and motivated the research community to develop some promising, state-of-the-art, and potential red phosphors to meet the necessary requirements. In this study, a series of Sm3+ (1–7 mol%) doped, Sm3+ (5%) doped and Eu3+ (2–5 mol%) co-doped Bi2O3 red phosphors were synthesized by a facile urea assisted auto-combustion process. The X-ray diffraction (XRD) analysis of the phosphors ascertains the tetragonal crystal structure without any trace of impurity. The UV-Vis-NIR absorption study of the phosphors was carried out in 200–1000 nm range and the estimated optical band gap of the phosphors was lying in the range of 2.778–2.831 eV. The photoluminescence (PL) emission studies were performed at an excitation wavelength of 481 nm in the 550–720 nm range. The effective energy transfer mechanism from Sm3+ to Eu3+ in the Bi2O3 phosphor has been ascribed to the dipole-dipole (d-d) interaction. The energy transfer process was further validated by PL decay time measurements. The CIE color coordinates were obtained using PL emission data. The CIE chromaticity diagram ascertains that the emission color of Bi2O3: Sm3+ phosphors were tuned from reddish-orange to the red region by varying the concentration of Eu3+ ions. The temperature dependent PL study of the phosphors was taken out in the range of 293–453 K and was found thermally stable at elevated temperatures.

Light-Stimulated Luminescence Control of Lead Halide-Based Perovskite Nanocrystals Coupled with Photochromic Molecules via Electron and Energy Transfer.

Photoswitchable nanomaterials are key materials in the development of advanced imaging techniques, such as super-resolution fluorescence microscopy. The combination of perovskite CsPbBr3 nanocrystals (NCs) with bright photoluminescence (PL) emission and diarylethenes (DAEs) with structural changes in response to ultraviolet (UV) and visible light is a promising candidate system. Herein, CsPbBr3 NCs are coupled with photochromic DAE molecules to control the PL emission from the NCs by light stimulation. The PL emission is successfully switched ON and OFF by alternating UV and visible light irradiation. Time-resolved PL emission studies suggest that Förster resonance energy transfer from CsPbBr3 NCs to the closed-ring form of DAE occurs after UV irradiation, and the PL emission is quenched. Upon visible-light irradiation, DAE is converted to the open-ring isomer, and the PL emission is restored. Femtosecond pump-probe spectroscopy reveals that light stimulation induces not only energy transfer but also photoinduced electron transfer in the NC-DAE pair on the picosecond timescale to form DAE radicals. Thus, it is suggested that the holes residing in the NCs react with the NCs, degrading the PL emission. Stable PL switching is realized using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a hole scavenger to avoid the reaction between the holes and NCs.

Structure, morphology and optical analysis of Dy3+ -doped Li6AlGd(BO3)4 phosphors for lighting applications

New and low energy consumption Li6AlGd(BO3)4: Dy3+ phosphors were fabricated through solid-state-reaction technique and characterized for lighting applications. The crystalline phase was confirmed from the powder X-ray diffraction technique. The Fourier transform infrared analysis was employed to investigate the presence of different bondings. The distribution of particles and their agglomeration was examined via morphological studies. Photoluminescence excitation, emission and decay studies were employed to study the luminescence properties. The excitation wavelength was optimized as 350 nm for efficient and strong luminescence from Li6AlGd(BO3)4: Dy3+ phosphors. They emit efficient luminescence through 4F9/2 → (6H15/2, 6H13/2, 6H11/2) transitions when excited at 350 nm near-UV wavelength. The photometric parameters such as chromaticity coordinates, colour purity and correlated colour temperature were determined using the emission spectral results. The quantum efficiency and the quantum yield parameters of studied phosphors show their applicability for lighting devices. The Li6AlGd(BO3)4: xDy3+ phosphor with x = 1.0 mol% has highest proficiency for lighting applications.

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.

Optical properties of Sr3Gd(PO4)3: Eu3+ phosphors for white LED sources

The SGPEux phosphors of composition Sr3Gd(1–x)(PO4)3:xEu3+ were synthesized by modified citrate-gel combustion method for white LED sources. The optimum conditions of synthesis were obtained from thermogravimetric and differential scanning calorimetry. The synthesized phosphors were crystallized into BCC structure with JCPDS No. 29–1301. The presence of various bonds due to stretching and bending vibrations of different functional groups were studied through Fourier transform infrared spectroscopy. The morphology was examined using high-resolution scanning electron microscopy. The luminescence analysis was carried out through photoluminescence excitation and emission studies. The charge transfer band and f-f transitions of Gd3+ and Eu3+ ions cause a transfer of energy from Gd3+ to Eu3+. A suitable excitation wavelength for efficient luminescence was selected as 273 nm by studying the emission properties at different excitations. The quenching in luminescence noticed beyond 2.0 mol% was assigned to non-radiative transitions at higher Eu3+ concentrations. The analysis of colour perception and colour temperature of emitted luminescence was studied using chromaticity coordinates evaluated from the emission spectra. The observed results suggest that the 2.0 mol% of Eu3+ doped SGPEu phosphor has more proficiency to design new class of w-LED sources.

Study of structural and optical properties of europium ion activated bismuth oxide nanophosphors

The current study examines the structural and optical features of un-doped and a series of Eu3+ ion-doped bismuth oxide nanophosphors synthesized via a facile, low-cost, and room temperature co-precipitation route. X-ray diffraction (XRD) analysis confirms the monoclinic crystal structure without any trace of impurity. The FTIR spectroscopic analysis of the samples has been taken in 400–4000 cm−1 wavenumber range to analyze the bonding states and functional groups of the species. Optical properties of the samples have been investigated using UV–Vis and photoluminescence (PL) spectroscopy. We observed a slight increase in the band gap in the doped samples (2.79–2.81 eV) as compared to the bismuth oxide host (2.77 eV). The photoluminescence emission studies have been carried out under 466 nm excitation wavelength over the range of 550–750 nm. The most prominent peak in the emission spectra is observed at 612 nm corresponding to(5D0 → 7F2)transition of Eu3+ ion. An explicit augmentation in the emission intensity is observed in 7 mol% Eu3+ doped Bi2O3 nanophosphor. The emission spectra were used to calculate the CIE chromaticity coordinates and CCT of the phosphors. The CIE coordinates depict an evident red-shift in the Eu3+ doped phosphors. The CCT values have been sufficiently alleviated after Eu3+ doping. Thus, our study corroborates an evident red-shift in the aforementioned optimized composition and suggests that it is a potential candidate for lighting and display devices.

Reddish-orange luminescence enhancement via Li+ co-doping in Sm3+ doped Bi2O3 nano-sheets

This paper presents a report on the correlation between structural, morphological, and luminescence properties of a series of Sm3+ (1–7 mol %) doped and Li+ (0.5–3 mol %) co-doped Bi2O3 nano-sheets synthesized via co-precipitation method. The X-ray diffraction (XRD) study ascertains monoclinic phase of the prepared samples. Average crystallite size and strain values have been estimated using Debye-Scherrer and Williamson-Hall methods, which exhibits an improved crystalline nature and reduced strain upon Li+ co-doping. X-ray photoelectron spectroscopy (XPS) has been carried out to explore the chemical composition and oxidation state of the elements present in the sample surface. The UV–Vis spectroscopy has been implemented to investigate the band gap of the samples. A slight increment is observed in the band gap upon doping as well as co-doping. An excitation wavelength of 481 nm has been used to explicate the photoluminescence (PL) emission studies over the range of 540–740 nm. Two-fold enhancement in the emission intensity of the Li+ co-doped samples has been recorded as compared to the Sm3+ doped Bi2O3 samples which make them worthy to be served as exquisite candidates to realize efficient warm white light emitting diodes (wLEDs).

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.

Always cubes: A comparative evaluation of gas phase synthesis methods and precursor selection for the production of MgO nanoparticles

MgO nanocubes are well-suited for the study of defects and interfaces inside metal oxide powders and ceramics. We evaluated the synthesis of MgO nanocubes via flame spray pyrolysis (FSP) and compared the structural and spectroscopic particle properties with materials obtained by chemical vapor synthesis (CVS). Characterization of the as-synthesized and vacuum annealed powder samples revealed slightly larger particle sizes for the FSP material that is absolutely comparable to CVS powders in terms of the particles structural definition, morphology and crystallinity. Moreover, optical absorption and photoluminescence emission studies show fingerprints, which are characteristic of MgO nanocrystals with a high abundance of grain corners, kinks and edges. The opportunity to synthesize MgO nanoparticles of high structural definition via FSP at significantly larger production rates and lower costs compared to CVS carries great potential to upscale powder production to generate MgO based functional oxide nanocomposites for ceramics and catalysis.

In-Situ Grown ZnS Nanoparticles on Amorphous Carbon Nanotubes Improved Cold Cathode Emission and Photoluminescence.

The current work reveals notable increase in field emission and photoluminescence characteristics of amorphous carbon nanotubes after forming its composite with In-Situ grown zinc sulfide (ZnS) nanoparticles. An easy chemical technique was employed to synthesize amorphous carbon nanotubes (ACNTs) and then ZnS nanoparticles were grown on them through an In-Situ solvothermal process. The morphology of the ZnS-ACNTs hybrid material was investigated through scanning electron microscope. Photoluminescence and field emission studies of the material were carried out as well in order to realize the applications. Substantial increase in photoluminescence intensity was found for ZnS-ACNTs hybrid material in comparison with pure amorphous carbon nanotubes, the hybrid also turned out as a better field-emitter than pure amorphous carbon nanotubes. Turnon field for ZnS-ACNTs composite decreased to 6 Vμm-1 which was 8 Vμm-1 in case of pure amorphous carbon nanotubes. A simulation analysis following finite element modelling method was carried out which ensured the improvement as field emitter for amorphous carbon nanotubes after ZnS nanoparticles were grown on them. Altogether the hybrid material proved to be a potential candidate for luminescent and cold cathode applications.

An insight into the luminescent properties and Judd–Ofelt analysis of Eu3+ doped CaZn2(PO4)2 phosphors

A batch of Eu3+ doped CaZn2(PO4)2 orange–red emitting phosphors were synthesized by the conventional high temperature solid state reaction method. The structural, morphological and spectroscopic properties of the prepared samples were investigated by experimental and theoretical studies. Powder XRD and FTIR results were used to evaluate the structural aspects of the prepared phosphors and morphology was investigated by TEM analysis. The elemental composition analysis of the representative sample was made using energy dispersive x-ray spectroscopy (EDS). The optical properties were analyzed with the aid of UV–Vis-NIR spectroscopy and photoluminescence (PL) spectroscopy. The PL excitation spectra revealed that the prepared phosphors can be efficiently excited under 393 nm that matches well with the dominant emission band of near UV- LED chip. The PL emission studies demonstrate the emission of an orange–red light with CIE coordinates (0.6075, 0.3920) with color purity 100.0% under an excitation of 393 nm. The maximum emission intensity was observed at Eu3+ concentration of 4 mol%, from which the critical distance (Rc = 1.98 nm) of quenching was calculated. The emission spectra were further used to interpret the site symmetry of Eu3+ ions. Judd–Ofelt theory was employed to predict various radiative properties such as branching ratio (βr), total transition probability (AT), radiative life time (τcalc) and stimulated emission cross section (σe). The thermal stability of the prepared phosphor was investigated using temperature dependent luminescence spectra and the emission intensity was observed to remain at 70.83% of its initial value when the temperature is raised from 310 K to 430 K. The decay kinetics analysis confirms the lifetime of the activator ions to be in the millisecond (ms) range. The better stimulated emission cross section and strong orange–red emission suggest the Eu3+ doped CaZn2(PO4)2 system as a promising candidate in the design of various optoelectronic devices such as phosphor converted LEDs (pc- LEDs) and display panels.

Germanium Tin Surface Passivation and Its Effect on the Optoelectronic Performances

Germanium Tin is an emerging semiconductor, with high carrier mobility and tunable bandgap directness and energy, that has been attracting a great deal of interest for applications in silicon-compatible electronics and monolithic optoelectronics. In contrast to compound semiconductors which have in the limelight to address several challenges in these technologies, this new emerging family of silicon-compatible group IV semiconductors holds the promise to combine both cost effectiveness and performance in several devices such as tunnelling field effect transistors, infrared detectors and emitters. By tuning strain and composition of GeSn, the band structure can be modified, thus allowing to engineer a large variety of low-dimensional heterostructures relevant to these devices. In fact, even though Ge is an indirect bandgap material, the incorporation of Sn in its lattice allows a transition into a direct bandgap material. Thus, GeSn yields to higher rate of radiative transitions and band-to-band tunneling. However, there are still several outstanding challenges at the materials level that must be overcome before harnessing GeSn advantageous properties. For instance, effective processes to effectively passivate its surface at various Sn composition are yet to be established. It is known that the surface of a semiconductor contains electronically active states because of unsaturated surface bonds or dangling bonds states, which act as localized energy levels the band gap that can change the intrinsic electrical behavior of the material. Therefore, understanding and controlling the surface states are of compelling importance. Moreover, the native oxide layer that forms at the surface of GeSn contains defects resulting in trapping charge carriers thus decreasing their mobility. The poor quality of the surface can decrease the rate of radiative transitions and contribute to the dark current. An effective passivation is thus needed to enhance the optoelectronic performances of GeSn. Passivation layer allows improved charge-separation, reduces charge recombination at surface states, passivates the dangling bonds and decreases the reactivity of the surface. To address these issues, this work investigates several chemical passivation processes and evaluate their effects on the optoelectronic properties of GeSn.The GeSn samples investigated in this work were grown on silicon wafers using ~0.6-3 µm-thick Ge interlay – commonly known as virtual substrates (Ge-VS). The epitaxial growth was carried out by the chemical vapor deposition (CVD) using monogermane (GeH4) and tin-tetrachloride (SnCl4) precursors. Strain minimization and the reduced growth temperature below 350 °C are of paramount importance to enhance Sn incorporation in Ge lattice to reach compositions of 7 – 17 at.%, much larger than the equilibrium composition of 1at.%. Several passivation treatments were evaluated and their basic mechanisms were elucidated. We first evaluated the capacity to remove the native oxide, leave the surface clean and passivate the dangling bonds of GeSn. The kinetic of oxide regrowth was studied to assess the chemical stability of the passivation through X-rays photoelectron spectroscopy (XPS) analysis. For instance, for a surface treatment consisting of a dip in HF followed by a dip in (NH4)2S and then by a nitride drying. XPS measurements show that it is effective in cleaning and passivating the surface, it allows removing the major part of Ge and Sn oxides. Recorded spectra reveal that this treatment gives rise to a persistent sulfur bonds at 161.8 eV, which is the signature of sulphide compounds. Sulfur allows surface passivation and slows down the oxide regrowth. Moreover, alternative surface passivation processes will also be discussed, and their performances compared to the treatment above will be elucidated. Besides, to better understand the evolution of the surface state after the treatments, ellipsometric measurements combined with atomic force microscopy studies are conducted and will be presented. Also, complementary electrical measurements and photoluminescence emission studies will also be discussed to highlight the effectiveness of each treatment in improving the optoelectronic performances of GeSn.

(Invited) (Si)GeSn Semiconductors for Integrated Optoelectronics, Quantum Electronics, and More

Sn-containing group IV semiconductors (Si)GeSn represent a versatile platform to implement a variety of Si-compatible photonic, optoelectronic, and photovoltaic devices. 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. In this presentation, we will discuss the recent progress in the growth of metastable (Si)GeSn semiconductors. We will highlight the current understanding of their fundamental properties and elucidate the effects of the atomistic-level structure on their optoelectronic performance. The relevance of these semiconductors for Si-compatible mid-infrared optoelectronics and quantum information will also be discussed form both materials and device perspectives. The (Si)GeSn multi-layer heterostructures discussed in this work have a Sn content reaching ~20at.% grown in a chemical vapor deposition (CVD) reactor on 4-inch Silicon wafers, using Monogermane (GeH4) and tin-tetrachloride (SnCl4) precursors, and disilane (Si2H6). By reducing the growth temperature, the Sn content in the alloy is increased, while preserving a high degree of crystal quality for the heterostructure in the topmost Sn-rich layer. No threading dislocations are observed in the upper layers, while misfit and edge dislocations remain mainly confined in the low Sn content layers underneath and in the proximity with the Ge-GeSn interface. By comparing multiple sample series with different strain and composition we demonstrate that the growth rate and the choice of the Ge hydride gas precursor play a limited role in enhancing the incorporation of Sn in the Ge lattice. However, strain minimization and the reduced growth temperature below 350 °C are of paramount importance to achieve Sn-rich GeSn semiconductors.[2,3] Atom probe tomography (APT) measurements will be discussed to address the abruptness of the interfaces in the GeSn multi-layer heterostructure and the composition uniformity.[2] The absence of short-range atomic ordering and Sn precipitates is estimated from the extended statistical APT analyses. Positron annihilation lifetime spectroscopy (PAS) and depth-profiled Doppler broadening measurements will be presented and discussed to elucidate the behavior of point defects in these semiconductors. Based on these analyses, we found that divacancies are the predominant type of point defects in GeSn.[4] Surprisingly, the increase in Sn content in the alloy yields an increase in the concentration of divacancies together with a small reduction in vacancy clusters. The interaction and possible pairing between Sn and vacancies have been proposed to explain the reduced formation of larger vacancy clusters in GeSn with higher Sn content. Photoluminescence (PL) emission studies will be described. In our GeSn with a Sn content of 18at.% the room temperature PL emission was found to be centered at 0.36 eV (i.e. 3.5 μm wavelength).[2] However, the compressive in-plane strain (-1.3 %) in these GeSn layers reduces the directness of the alloy, leading to a higher energy gap value. By releasing the strain down to -0.2% in the 18 at.% Sn layer using a fully-underetched micro-disk geometry, a 50 meV red-shift of the PL emission energy down to 0.31 eV (i.e. 4.0 μm wavelength) is obtained. Moreover, the strained and relaxed PL emission and reflectance measurements ranging from 300K down to 4K will be shown. These observations will be discussed in the light of photocurrent measurements and photodetector performance. Finally, we will also discuss the use of GeSn as a platform to develop highly tensile strained Ge quantum wells (QWs. These low-dimensional systems, made possible by the availability of GeSn templates, create a wealth of opportunities to design and fabricate new quantum devices. For instance, unlike the compressively strained QWs, the top of the valence band is of light hole (LH) type under tensile strain, thus corresponding to a much smaller effective mass and ½ spin. These characteristics, combined with high hole mobility and strong spin-orbit coupling in Ge, make tensile strained Ge QWs more attractive for hole spin qubits. Acknowledgements The authors thank J. Bouchard for the technical support with the CVD system. O.M. acknowledges support from NSERC Canada (Discovery, SPG, and CRD Grants), Canada Research Chairs, Canada Foundation for Innovation, Mitacs, PRIMA Québec, and Defence Canada (Innovation for Defence Excellence and Security, IDEaS).

Tuning of emission from copper-doped ZnSe quantum dots

In this paper, different concentrations of copper-doped zinc selenide quantum dots (Cu:ZnSe QDs) were synthesized and compared with differently sized (2.0–3.7 nm) Cu:ZnSe QDs by keeping the concentration of Cu fixed at 5%. In both cases a high-temperature wet chemical route was employed for synthesis. As the concentration of Cu increased from 2.5% to 12.5% in the solution, a clear redshift was observed in the absorption spectrum, which is an indication that Cu ions have been incorporated into the host lattice. In order to identify the state in which the Cu ions are present, electron paramagnetic resonance (EPR) studies were carried out on the samples. The EPR spectra reveal a resonance signal which is characteristic of Cu2+ ions. With an increase in concentration of Cu ions it is found that the component increases. Photoluminescence emission and excitation studies revealed both band-edge and Cu-related emission, further strengthening the incorporation of Cu ions in the host lattice.

Radio frequency plasma polymerized thin film based on eucalyptus oil as low dielectric permittivity, visible and near-infrared (NIR) photoluminescent material

Thin films derived from eucalyptus oil was fabricated on glass and silicon substrate by rf plasma polymerization technique and characterized by FTIR, FESEM, AFM, Ellipsometry, UV–Visible and Photoluminescence spectroscopy. The dielectric constant and dielectric loss of the thin films were estimated using spectroscopic ellipsometry technique. Functional groups related to chromophores present in the eucalyptus oil thin films were identified using FTIR spectroscopy. π − π* interband transitions (306 nm) and intramolecular charge transfer (556 nm) was observed from the absorption spectra of the polymerized thin films. The indirect optical band gap estimated using Tauc plot was 3.66 eV, which revealed the semiconducting nature of the thin film. The value of real part of dielectric constant (ϵ′) was less than 2.44, which indicated a low dielectric permittivity behaviour of the film in the optical regime. The photoluminescence emission studies and CIE colour coordinates showed that plasma polymerized eucalyptus oil thin films exhibits yellow and IR emission.

Vanadium pentoxide nanorods in latent finger print detection

Nanostructures contribute vital applications for surface-based science including latent fingerprints (LFPs) detection and reconstruction. Fingerprints are unique to an individual, matching the finger prints help to identify culprits. Vanadium Pentoxide (V2O5) nanorods were synthesized via hydrothermal method using pomegranate peel extract as fuel, towards their use in fingerprint development. PXRD patterns confirmed the formation of orthorhombic V2O5 crystal structure. Raman vibration modes at 144 cm−1 and 994 cm−1 signifies the characteristic orthorhombic V2O5 structural formation, FTIR spectra shows vibration bands of V2O5, UV–vis spectroscopy shows an intrinsic absorption band at ∼418 nm corresponding to electron transitions (O2p → V3d). The energy band gap (Eg) estimated from absorption spectrum was found to be ∼2.35 eV. Formation of nanorods was observed from SEM micrographs and particle size was found to be 30 nm from TEM images. Photoluminescence emission studies were performed and yellow –orange (brown) emission was observed from CIE diagram. The characteristic brown/Yellow-orange color of V2O5 nanorods supports tracing of LFPs on many kind of surfaces in visible light which eliminates the need for illuminating source. Hence, V2O5 nanorods find potential application in Forensic sciences.

Effects of methyl violet dye on the growth and properties of zinc (tris) thiourea sulfate single crystals

In this study, we investigated the monocrystal growth and characteristics of pure and methyl violet (MV) dyed zinc(tris) thiourea sulfate (ZTS) large size single crystals. The morphology of ZTS was modified in the presence of MV dye. The crystals were crushed for a finite time to obtain powders for X-ray diffraction analysis and the lattice parameters were determined. The crystals were analyzed based on Fourier transform-Raman spectroscopy measurements and the vibrational modes were identified. Some extra vibrational modes were observed due to the presence of the MV dye. Ultraviolet–visible–near infrared optical absorbance measurements were recorded and the band gap was calculated. A large band gap ∼4.31 eV was obtained for the ZTS crystals, which supports their possible application in electro-optic devices. Two absorption bands at around 584 nm (sharp) and ∼362 nm (broad) were also observed in the dyed crystals but not in the pure crystals, thereby indicating the interaction between the dye and ZTS. Photoluminescence (PL) emission studies were conducted at an excitation wavelength of 360 nm. PL emission peaks were observed at ∼433 nm in the pure crystals, and at ∼421 and 444 ± 5 nm in the dyed crystals. Differential scanning calorimetry demonstrated the increased melting temperature of ZTS in the presence of the dye. The dielectric constant, ac electrical conductivity, and mechanical strength were higher for the dyed crystals. Our results suggest that the dyed crystals may be more suitable for applications in opto-electronic devices compared with the pure crystals.

A comparison of temperature dependent photoluminescence and photo-catalytic properties of different MoS2 nanostructures

Here, a comparison of optical absorption, photoluminescence (PL) emission and catalytic properties of hydrothermally synthesized MoS2 nanoplatelets (MNPs), a few-layer MoS2 nanosheets (MNSs), and MoS2 nanorods (MNRs) have been done, which is rarely available in the literature. The formation of MNSs has been confirmed by transmission electron microscopy, field emission scanning electron microscopy, and Raman spectra analyses. In UV–Vis absorption and PL emission spectra of colloidal aqueous dispersions of the samples, ‘A’ and ‘B’ excitonic peaks having energy separation of ∼219 meV are clearly observed. The ‘D’ excitonic band-gap at 0 K of MNSs has been calculated to be 3.21 eV from the temperature-dependent PL emission studies. A thermodynamic approach has been employed to understand the adsorption of methylene blue (MB) dye onto MNPs, MNRs, and MNSs at various temperatures and it is revealed that the adsorption process is spontaneous, endothermic, and physisorption in nature. The equilibrium adsorption capacities of the samples are found out to be 7.75, 7.67, and 10.17 mg/g, respectively of MNPs, MNRs, and MNSs at room temperature. It is found that MNSs, having large specific surface area and a large number of active sites, exhibit a relatively higher photo-catalytic activity than those of MNPs and MNRs. In case of MNSs, the obtained value of hydrogen evolution reaction (HER) onset overpotential of −49 mV (vs. reversible hydrogen electrode) which is much smaller than those of MNPs and MNRs. The relatively lower Tafel slope of 38 mV/dec of MNSs suggests that these can act as the best electrocatalyst amongst MNSs, MNPs, and MNRs. Thus, it has been revealed that a few layered 2D MoS2 nanosheets are the best candidate for degradation of hazardous organic dye and HER activity in compared to MoS2 nanoplatelets and nanorods.