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An environmentally safe chemical process was used to create the CdSe nanocomposite films in a polyvinyl alcohol (PVA) matrix. X-ray diffraction was used to analyze these composites, revealing the cubic zinc blend structure of CdSe/PVA nanocomposite with crystal sizes as small as a few nm. These composite films have had their photoluminescence (PL) properties examined. At 420nm, the PL peak of CdSe/PVA was detected. The CdSe/PVA nanocomposite’s mechanoluminescence properties were investigated. It is found that the impact velocity determines the ML intensities. When ML is produced impulsively by the impact of a moving piston on the nanocomposite, two peaks in ML intensity arise with time, and it is found that the mechanoluminescence intensity is dependent on the magnitude of impact velocity. ML peak intensities of the first and second peaks ($I_{m1}$ and $I_{m2})$ increase with increasing impact velocity. However, the time corresponding to the first and second maxima ($t_{m1}$ and $t_{m2})$ shifts towards shorter time values with greater impact velocity. We examined the voltage-brightness and voltage-current characteristics curves for our electroluminescence investigations of CdSe/PVA nanocomposite. At higher frequencies, EL with greater brightness at low threshold voltage has been seen.

In this study, a series of Gd${}^{3+}$, Ce${}^{3+}$ doped Sr₂P₂O₇ phosphors synthesized by a novel method utilizing stearic acid sol–gel are reported. Structural analysis performed by X-ray diffraction (XRD) pattern revealed that doping of trivalent lanthanide ions did not change the orthorhombic structure possessed by Sr₂P₂O₇ matrix and also confirmed the phase purity and crystallinity of the phosphor. Scanning electron microscopy (SEM) micrograph confirms its surface morphology and particle size in the range of 50nm to $1\mu$m. Photoluminescence (PL) studies revealed that PL emission for Gd${}^{3+}$ and Ce${}^{3+}$-doped Sr₂P₂O₇phosphor gives significant emissions which are suitable for application in UV-LEDs for phototherapy portable devices.

A series of singly and co-doped LiTi₂(PO${}_4{)}_3$:Eu${}^{3+}$, Tb${}^{3+}$ phosphors prepared by solid state metathesis (SSM) was reported the first time. The X-Ray diffraction (XRD) verified that the as-prepared materials exhibit a pure rhombohedral phase with a space group of P2₁/m. Scanning electron microscopy (SEM), Energy Dispersive X-ray analysis (EDAX) and elemental mapping confirm the morphology and constituents of elements. The LiTi₂(PO${}_4{)}_3$:Eu${}^{3+}$ shows 614nm red emission obtained due to the ⁵D${}_0{\to }^7$L₆ transition under 393nm excitation and the Tb${}^{3+}$ doped sample gives 546nm green emission ascribed to ⁵D${}_4{\to }^7$F₅ for excitation of 376nm. The luminescence properties of Eu${}^{3+}$/Tb${}^{3+}$ doped LiTi₂(PO${}_4{)}_3$ phosphors excited under a UV source were investigated and the relative mechanism was analyzed. Upon excitation by 393nm, the LiTi₂(PO${}_4{)}_3$:Eu_xTb_y phosphor has the capability to generate vivid green, yellow and red emissions, with color tunability achieved through the modulation of dopant ion concentrations. Color chromaticity of LiTi₂(PO${}_4{)}_3$:Eu${}_{0.01}$Tb${}_{0.05}$ gives at $x=0.574$, $y=0.425$ and $\mathrm{\text{CCT}}=1810.04$K. The proposed simple, low-cost, nontoxic and rapid synthesis route of phosphate-based compounds will lead the way to access these LiTi₂(PO${}_4{)}_3$:Eu${}^{3+}$/Tb${}^{3+}$ phosphors for potential applications in w-light-emitting diodes and plasma display panel.

Using the successive ionic layer adsorption and reaction (SILAR) method, we successfully deposited thin films (TFs) of both pure cadmium oxide (CdO) and strontium (Sr) CdO onto glass slides. Analysis of the films’ structure and morphology, conducted via field emission scanning electron microscopy and X-ray diffraction, revealed a polycrystalline cubic structure with porous nanoflake agglomerates. Further characterization involved ultraviolet–visible spectroscopy and photoluminescence spectrum measurements to explore the optical attributes of the CdO films. Notably, we observed significant impacts of Sr doping on both optical transmittance and photoluminescence emission intensity in the CdO nanostructures. Electrical measurements, carried out using four-probe Iviumstat analysis, demonstrated variations in resistivity with different levels of Sr doping. These findings highlight the potential for controlling specific physical features of CdO through Sr doping, making it a promising candidate for various device applications.

Spatially resolved oxidation of nanocrystalline silicon surfaces has been studied using Fourier Fourier-transformed infrared microscopy. At the same time, photoluminescence (PL) quenching has been recorded. Both characteristics are related to the increase of silicon oxide species on the sample surfaces. Illumination of surfaces by blue light increases oxidation rates and speeds PL quenching in the form of a stretched exponential function. A possible explanation of this behavior considering quantum dots and quantum wires present in the material is proposed.

A well-aligned single-crystalline barium titanate (BaTiO₃) nanostructured layer was prepared by the growth and conversion of vertically aligned TiO₂ nanorods. This was achieved through a two-step hydrothermal method on fluorine-doped tin oxide (FTO)-coated glass substrates via the dissolution-nucleation-recrystallization mechanism. The morphology, crystal structure and optical properties were investigated using field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and Z-scan techniques. The X-ray and selected area diffraction patterns (SAED) confirmed the formation of the aligned single-crystalline tetragonal BaTiO₃ layer. The room temperature Raman spectrum showed the tetragonal TiO₂-related vibrational modes in BaTiO₃. The PL spectra indicated the coalescence of band edge emissions of BaTiO₃ and TiO₂ in the blue and visible regions of the investigated spectra. The Z-scan experiments performed using the CW Nd:YAG laser revealed a positive nonlinear refractive index on the order of 10${}^{-7}$ cm²W${}^{-1}$, indicating the self-focusing type of cation in the BaTiO₃ sample. The nonlinear absorption coefficient of the BaTiO₃ nanostructures in the order of 10${}^{-7}$ cm W${}^{-1}$ was also calculated. As expected, the BaTiO₃ nanostructure synthesized in this study is a good candidate for use in nonlinear optics.

The bandgap is a fundamental property inherent to semiconductor materials such as silicon (Si) and germanium (Ge), determining their electronic and optical properties. Furthermore, combining Si and Ge allows for the potential to manipulate the optical and electronic properties of mixed materials. Various synthetic methods for Si/Ge nanoparticles (NPs) have been investigated, and there is a need to develop a simpler method for Si/Ge NP synthesis. We present a modified one-pot synthesis method to fabricate $n$-butyl Si/Ge NPs using a streamlined, room-temperature process that excludes surfactants. Ge–Ge, Ge–Si, and Si–Si optical phonons were exhibited by $n$-butyl-Si/Ge NPs at 285, 400, and 485cm${}^{-1}$, respectively, in Raman analysis. The Si-to-Ge ratios of the $n$-butyl-Si/Ge NPs ranged from 0.40:0.60 to 0.47:0.53 according to high-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDX) analysis. The PL spectrum (${\lambda }_{\mathrm{\text{em}}}=445$nm) of $n$-butyl-Si/Ge NPs closely resembled those of Ge NPs (${\lambda }_{\mathrm{\text{em}}}=438$nm); this result is discussed in relation to those obtained from reported theoretical calculations.

Two different kinds of ZnO nanoparticles (NPs) with distinct particle sizes were synthesized by a precipitation method. For the first time, the effects of two distinct sizes ZnO NPs on the growth, photoluminescence properties and kojic acid (KA) yield of Aspergillus oryzae (A. oryzae) were examined. The findings showed that ZnO-A and -B NPs, with average particle sizes of 11.93 nm and 34.41nm, respectively, exhibited a hexagonal crystal structure. It was found that when the concentration of NPs was below 100$\mu$g/mL, ZnO NPs were nontoxic and served as activators to stimulate the growth of A. oryzae, and the biomass of solid and liquid medium, the total integral emission intensity, the content of extracellular protein and total organic carbon and KA yield of A. oryzae grown with ZnO-A (ZnO-B) NPs were about 2.19 (1.97), 2.47 (1.56), 1.67 (1.16), 2.45 (1.95), 0.47 (0.50) and 2.07 (1.37) times more than that of control sample (without NPs), respectively.

100 mol% activator orthorhombic Tb₂(MoO₄)₃ green phosphors were prepared using a solid-state reaction method. The impact of sintering temperature on the crystalline phase structures, the compositions, the sizes and morphologies of particles, the values of energy bandgap ($E$${}_g$), the photoluminescence (PL) excitation and emission spectra, the fluorescence lifetimes, PL quantum yield (PLQY), and the luminescent thermal stabilities of the prepared material were comprehensively investigated. The particle size increased from 2.54 to 5.81 $\mu$m and the $E$${}_g$ decreased from 3.60 to 3.41 eV with the calcine temperature increased from $800^{\circ }\text{C}$ to $1100^{\circ }\text{C}$. The Tb₂(MoO₄)₃ green phosphor prepared at $1000^{\circ }\text{C}$ exhibited optimal PL intensity though it did not possess the highest PLQY with 380 nm excitation. Moreover, the sample prepared at $1000^{\circ }\text{C}$ showed better thermal stabilities than that prepared at $1100^{\circ }\text{C}$. The research proved the sintering temperature has great effects on the properties of Tb₂(MoO₄)₃ phosphors.

Rare-earth elements ${\text{Sm}}^{3+}$-, ${\text{Pr}}^{3+}$-, ${\text{Ho}}^{3+}$- and ${\text{Er}}^{3+}$-doped (${\text{K}}_{0.5}$${\text{Na}}_{0.5}$)${}_{0.974}$${\text{La}}_{0.025}$${\text{Nb}}_{0.975}$${\text{Bi}}_{0.025}$O₃ ceramics (abbreviated as KNLNB-0.1%RE) were prepared by conventional solid-phase sintering method. The structure, transparency, energy storage and photoluminescence properties of the samples are investigated. All ceramics have the pseudo-cubic phase structure without the impurity phase at room temperature. KNLNB-0.1%RE ceramics exhibit excellent optical transmittance, with KNLNB-0.1%Ho achieving 71.8% transmittance in the visible wavelength range (780nm) and largest effective energy storage density of 1.45J/cm³. In our experiments, rare-earth-doped KNLNB ceramics exhibit photoluminescence effects. This work facilitates the development of transparent energy storage ceramics with fluorescent effects.

This account presents a survey of recent advances in quantum-dot research and technology and highlights trends of key significance as they relate to the emerging applications of quantum-dot technology in biology.

Optical properties of green emission Ga_0.80In_0.20N/GaN multi-quantum well and light emitting diode have been investigated by using photoluminescence, cathodoluminescence, electroluminescence, and photoconductivity. The temperature dependent photoluminescence and cathodoluminescence studies show three emission bands including GaInN/GaN quantum well emission centered at 2.38 eV (~ 520 nm). The activation energy of the non-radiative recombination centers was found to be ~ 60 meV. The comparison of photoconductivity with luminescence spectroscopy revealed that optical properties of quantum well layers are strongly affected by the quantum-confined Stark effect.

The formation of nano sized Si structures during the annealing of silicon rich oxide (SRO) films was investigated. These films were synthesized by low pressure chemical vapor deposition (LPCVD) and used as precursors, a post-deposition thermal annealing leads to the formation of Si nano crystals in the SiO₂ matrix and Si nano islands (Si nI) at c-Si/SRO interface. The influences of the excess Si concentration, the incorporation of N in the SRO precursors, and the presence of a Si concentration gradient on the Si nI formation were studied. Additionally the influence of pre-deposition substrate surface treatments on the island formation was investigated. Therefore, the substrate surface was mechanical scratched, producing high density of net-like scratches on the surface. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize the synthesized nano islands. Results show that above mentioned parameters have significant influences on the Si nIs. High density nanosized Si islands can epitaxially grow from the c-Si substrate. The reported method is very simple and completely compatible with Si integrated circuit technology.

GaAs and InP based III-V compound semiconductor nanowires were grown epitaxially on GaAs (or Si) (111)B and InP (111)B substrates, respectively, by metalorganic chemical vapor deposition using Au nanoparticles as catalyst. In this paper, we will give an overview of nanowire research activities in our group. In particular, the effects of growth parameters on the crystal structure and optical properties of various nanowires were studied in detail. We have successfully obtained defect-free GaAs nanowires with nearly intrinsic exciton lifetime and vertical straight nanowires on Si (111)B substrates. The crystal structure of InP nanowires, i.e., WZ or ZB, can also be engineered by carefully controlling the V/III ratio and catalyst size.

High radiative efficiency in moderately doped n-InP results in the transport of holes dominated by photon-assisted hopping, when radiative hole recombination at one spot produces a photon, whose interband absorption generates another hole, possibly far away. Due to "heavy tails" in the hop probability, this is a random walk with divergent diffusivity (process known as the Lévy flight). Our key evidence is derived from the ratio of transmitted and reflected luminescence spectra, measured in samples of different thicknesses. These experiments prove the non-exponential decay of the hole concentration from the initial photo-excitation spot. The power-law decay, characteristic of Lévy flights, is steep enough at short distances (steeper than an exponent) to fit the data for thin samples and slow enough at large distances to account for thick samples. The high radiative efficiency makes possible a semiconductor scintillator with efficient photon collection. It is rather unusual that the material is "opaque" at wavelengths of its own scintillation. Nevertheless, after repeated recycling most photons find their way to one of two photodiodes integrated on both sides of the semiconductor slab. We present an analytical model of photon collection in two-sided slab, which shows that the heavy tails of Lévy-flight transport lead to a high charge collection efficiency and hence high energy resolution. Finally, we discuss a possibility to increase the slab thickness while still quantifying the deposited energy and the interaction position within the slab. The idea is to use a layered semiconductor with photon-assisted collection of holes in narrow-bandgap layers spaced by distances far exceeding diffusion length. Holes collected in these radiative layers emit longwave radiation, to which the entire structure is transparent. Nearly-ideal calculated characteristics of a mm-thick layered scintillator can be scaled up to several centimeters.

The aim of this work is to provide an overview on the recent advances in the selective area growth (SAG) of (In)GaN nanostructures by plasma assisted molecular beam epitaxy, focusing on their potential as building blocks for next generation LEDs.

The first three sections deal with the basic growth mechanisms of GaN SAG and the emission control in the entire ultraviolet to infrared range, including approaches for white light emission, using InGaN disks and thick segments on axial nanocolumns. SAG of axial nanostructures is developed on both GaN/sapphire templates and GaN-buffered Si(111).

As an alternative to axial nanocolumns, section 4 reports on the growth and characterization of InGaN/GaN core-shell structures on an ordered array of top-down patterned GaN microrods. Finally, section 5 reports on the SAG of GaN, with and without InGaN insertion, on semi-polar (11-22) and non-polar (11-20) templates. Upon SAG the high defect density present in the templates is strongly reduced as indicated by a dramatic improvement of the optical properties. In the case of SAG on non-polar (11-22) templates, the formation of nanostructures with a low aspect ratio took place allowing for the fabrication of high-quality, non-polar GaN pseudo-templates by coalescence of these nanostructures.

An algorithm for fast calculation of theoretical deep level photoluminescence (PL) lineshapes is presented. The algorithm can be used for effective comparison with experimental spectra in cases of bulk photoluminescence. The method was expanded and for the cases of deep level photoluminescence in quasi-two and quasi-one dimensional electron systems in semiconductors.

The relaxation dynamics of photo-excited states in single crystals of Alq₃, utilized as organic electroluminescent (EL) devices, have been investigated. The photoluminescence (PL) peak of Alq₃ changes depending on the exciting photon energy and the temperature. Nevertheless, a PL peak appears at the same energy position as the EL peak for excitations at energies above the transition edge and a new PL band has been resolved at energies below the EL peak for excitation at the lowest part of the absorption tail. However, for low temperatures and for excitation in the intermediate energy region of the absorption tail, a PL peak appears at the lower energy side. This PL peak shifts into the same energy as the EL peak with increasing temperature. This behavior is explained by a model which takes account of two luminescent states and one non-luminescent intermediate state. In the intermediate energy region, the temperature dependence of the PL for the excitation is also explained by a thermal activation process mediated by the non-luminescent state. The lifetimes of the three states obtained from the temporal profiles of the PL are understood consistently on the basis of this model.

Quantum wells with fractal-like interfaces arise in the growth of semiconductor heterostructures. Such fractal characteristics largely influence the optical and transport properties in these constrained geometries. We report a systematic study of growth through the study of optical properties. The spectra obtained show "anomalous behavior", whose characteristics depends on the growth procedure. The theoretical analysis was performed resorting to an unconventional statistical-mechanical formalism. It allows one to correlate growth conditions with surface roughness, and to determine their influence on experimental results, allowing one to obtain a picture of the physics involved in such systems.

We have studied the mangeto-photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) with different chiral vector indices (n,m). A novel strain method is used to assign the quantum number q and chiral vector indices. The PL intensities and energies were found to be a strong function of magnetic field at low temperature, but were field independent up to 19.5T at 300K. All emission energies show a significant red shift caused by the action of Aharanov-Bohm flux threading the tubes.