Showing papers on "Photoluminescence published in 2002"
TL;DR: The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques as discussed by the authors.
Abstract: The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques. These three characterization techniques show an energy gap for InN between 0.7 and 0.8 eV, much lower than the commonly accepted value of 1.9 eV. The photoluminescence peak energy is found to be sensitive to the free-electron concentration of the sample. The peak energy exhibits very weak hydrostatic pressure dependence, and a small, anomalous blueshift with increasing temperature.
1,378 citations
TL;DR: An N-doped p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating, N-O substrate as discussed by the authors.
Abstract: An N-doped, p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating ZnO substrate. Hall-effect and conductivity measurements on the layer give: resistivity=4×101 Ω cm; hole mobility=2 cm2/V s; and hole concentration=9×1016 cm−3. Photoluminescence measurements in this N-doped layer show a much stronger peak near 3.32 eV (probably due to neutral acceptor bound excitons), than at 3.36 eV (neutral donor bound excitons), whereas the opposite is true in undoped ZnO. Calibrated, secondary-ion mass spectroscopy measurements show an N surface concentration of about 1019 cm−3 in the N-doped sample, but only about 1017 cm−3 in the undoped sample.
1,237 citations
TL;DR: These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots.
Abstract: Reversible electrochemical injection of discrete numbers of electrons into sterically stabilized silicon nanocrystals (NCs) (∼2 to 4 nanometers in diameter) was observed by differential pulse voltammetry (DPV) in N , N ′-dimethylformamide and acetonitrile. The electrochemical gap between the onset of electron injection and hole injection—related to the highest occupied and lowest unoccupied molecular orbitals—grew with decreasing nanocrystal size, and the DPV peak potentials above the onset for electron injection roughly correspond to expected Coulomb blockade or quantized double-layer charging energies. Electron transfer reactions between positively and negatively charged nanocrystals (or between charged nanocrystals and molecular redox-active coreactants) occurred that led to electron and hole annihilation, producing visible light. The electrogenerated chemiluminescence spectra exhibited a peak maximum at 640 nanometers, a significant red shift from the photoluminescence maximum (420 nanometers) of the same silicon NC solution. These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots.
969 citations
TL;DR: In this article, the size control of SiO/SiO2 superlattices with an upper limit of the nanocrystal sizes of 3.8, 2.5, and 2.0 nm was investigated.
Abstract: Phase separation and thermal crystallization of SiO/SiO2 superlattices results in ordered arranged silicon nanocrystals. The preparation method which is fully compatible with Si technologies enables independent control of particle size as well as of particle density and spatial position by using a constant stoichiometry of the layers. Transmission electron microscopy investigations confirm the size control in samples with an upper limit of the nanocrystal sizes of 3.8, 2.5, and 2.0 nm without decreasing the silicon nanocrystal density for smaller sizes. The nanocrystals show a strong luminescence intensity in the visible and near-infrared region. A size-dependent blueshift of the luminescence and a luminescence intensity comparable to porous Si are observed. Nearly size independent luminescence intensity without bleaching effects gives an indirect proof of the accomplishment of the independent control of crystal size and number.
764 citations
TL;DR: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy as discussed by the authors, and growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction.
Abstract: Wurtzite InN films were grown on a thick GaN layer by metalorganic vapor phase epitaxy. Growth of a (0001)-oriented single crystalline layer was confirmed by Raman scattering, x-ray diffraction, and reflection high energy electron diffraction. We observed at room temperature strong photoluminescence (PL) at 0.76 eV as well as a clear absorption edge at 0.7–1.0 eV. In contrast, no PL was observed, even by high power excitation, at ∼1.9 eV, which had been reported as the band gap in absorption experiments on polycrystalline films. Careful inspection strongly suggests that a wurtzite InN single crystal has a true bandgap of 0.7–1.0 eV, and the discrepancy could be attributed to the difference in crystallinity.
692 citations
TL;DR: In this paper, the enhancement of luminescence of (CdSe)ZnS core−shell quantum dots on gold colloids as a function of semiconductor nanocrystal−metal nanoparticle distance was studied.
Abstract: We have studied the enhancement of luminescence of (CdSe)ZnS core−shell quantum dots on gold colloids as a function of semiconductor nanocrystal−metal nanoparticle distance. Using a layer-by-layer polyelectrolyte deposition technique to insert well-defined spacer layers between gold colloids and quantum dots, a distance-dependent enhancement and quenching of quantum dot photoluminescence has been observed. The maximum enhancement by a factor of 5 is achieved for a 9-layer spacer (≈11 nm). The efficient quantum dot excitation within the locally enhanced electromagnetic field produced by the gold nanoparticles is evidenced by the observation of the surface plasmon resonance in the photoluminescence excitation spectrum of (CdSe)ZnS nanocrystals.
661 citations
TL;DR: In this article, a Pechini sol−gel process combined with soft lithography was used to fabricate nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a pechini sol-gel process.
Abstract: Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol−gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM) and optical microscopy, UV/vis transmission and absorption spectra, photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 400 °C and the crystallinity increased with the increase of annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of grains with an average size of 90 nm. Patterned gel and crystalline phosphor film bands with different widths (5−60 μm) were obtained. Significant shrinkage and a few defects were observed in the patterned films during the heat treatment process. The doped rare earth ions (A) show...
638 citations
TL;DR: In this paper, the fundamental band gap for InN is shown to be near 0.8 eV and the band gap increases with increasing Ga content, which is well fit with a bowing parameter of ∼1.4 eV.
Abstract: High-quality wurtzite-structured In-rich In1−xGaxN films (0⩽x⩽0.5) have been grown on sapphire substrates by molecular beam epitaxy. Their optical properties were characterized by optical absorption and photoluminescence spectroscopy. The investigation reveals that the narrow fundamental band gap for InN is near 0.8 eV and that the band gap increases with increasing Ga content. Combined with previously reported results on the Ga-rich side, the band gap versus composition plot for In1−xGaxN alloys is well fit with a bowing parameter of ∼1.4 eV. The direct band gap of the In1−xGaxN system covers a very broad spectral region ranging from near-infrared to near-ultraviolet.
590 citations
TL;DR: In this paper, the photoluminescence spectrum of the ZnO/AAM assembly system depends on the excitation wavelength in the visible region, which is attributed to different types of oxygen vacancies in the znO nanowires.
551 citations
TL;DR: In this paper, the structureless green emission in ZnO was shown to be associated with Cu2+ ions, and it was shown that the unstructured green emission (observed before the high-temperature anneal) is don...
Abstract: Electron paramagnetic resonance (EPR), photoluminescence, and infrared optical absorption have been used to investigate a ZnO crystal before and after a thermal anneal for 1 h in air at 900 °C. The sample was an undoped high quality crystal grown by the chemical vapor transport method. In addition to shallow donor impurities, the crystal contained trace amounts of copper ions. Prior to the thermal anneal, these ions were all in the Cu+ (3d10) state and the observed luminescence at 5 K, produced by 364 nm light, consisted of a broad structureless band peaking at 500 nm. After the high-temperature anneal, the Cu2+ (3d9) EPR spectrum was observed and the luminescence had changed significantly. The emission then peaked near 510 nm and showed structure identical to that reported by Dingle [Phys. Rev. Lett. 23, 579 (1969)]. Our data reaffirm that the structured green emission in ZnO is associated with Cu2+ ions. We suggest that the unstructured green emission (observed before the high-temperature anneal) is don...
524 citations
TL;DR: The distribution of properties within ensembles of colloidally grown II-VI and III-V semiconductor nanocrystals was studied and a drastic difference in the photoluminescence efficiencies of size-selected fractions was observed, indicating a general character of the phenomenon observed.
Abstract: The distribution of properties within ensembles of colloidally grown II-VI and III-V semiconductor nanocrystals was studied. A drastic difference in the photoluminescence efficiencies of size-selected fractions was observed for both organometallically prepared CdSe and InAs colloids and for CdTe nanocrystals synthesized in aqueous medium, indicating a general character of the phenomenon observed. The difference in the photoluminescence efficiencies is attributed to different averaged surface disorder of the nanocrystals originating from the Ostwald ripening growth mechanism when larger particles in the ensemble grow at the expense of dissolving smaller particles. At any stage of growth, only a fraction of particles within the ensemble of growing colloidal nanocrystals has the most perfect surface and, thus, shows the most efficient photoluminescence. This is explained by a theoretical model describing the evolution of an ensemble of nanocrystals in a colloidal solution. In an ensemble of growing nanocrystals, the fraction of particles with the highest photoluminescence corresponds to the particle size having nearly zero average growth rate. The small average growth rate leads to the lowest possible degree of surface disorder at any given reaction conditions.
TL;DR: In this paper, single-crystalline zinc oxide (ZnO) nanowires with high density were successfully synthesized on nickel monoxide (NiO) catalyzed alumina substrate through a simple metal-vapor deposition method at an extremely low temperature (450 °C).
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TL;DR: In this article, a review of Si/Ge nanostructures that have been synthesized by self-assembling and self-ordering during heteroepitaxy of \mbox{silicon-germanium} alloys on single-crystal silicon substrates is given.
Abstract: A review is given on the formation mechanisms and the properties of Si/Ge nanostructures that have been synthesized by self-assembling and self-ordering during heteroepitaxy of \mbox{silicon-germanium} alloys on single-crystal silicon substrates. The properties of electronic subbands in smooth strained Si/SiGe quantum well structures are presented as a basis for characterizing coherent Si/Ge nanostructures with free motion of carriers in a reduced number of dimensions. The low-dimensional band structure of valence band states confined in strained Si/Ge and Si/SiGe nanostructures is analysed by optical and electrical spectroscopy. The nanostructures presented were fabricated by self-assembly induced by elastic strain relaxation without applying any patterning technique. Misfit lattice strain of SiGe material deposited on Si substrates can relax by bunching of atomic surface steps with SiGe agglomeration at the step edges or by nucleation of Ge-rich islands in the Stranski-Krastanow growth mode. The size, density and composition of such Si/Ge nanostructures representing quantum wires and dots, respectively, can be tuned in a wide range by the growth parameters. Local strain fields extending into the Si host influence the nucleation and the lateral arrangement of nanostructures in subsequent layers and can be applied for self-ordering of nanostructures in the vertical as well as the lateral direction. Interband and intra-valence-band photocurrent, absorption and photoluminescence spectroscopy as well as C-V and admittance measurements reveal a consistent view of the band structure in Si/Ge quantum dot structures. This is in good agreement with model calculations based on band offsets, deformation potentials and effective electron masses known from earlier studies of Si/SiGe quantum well structures. The effective valence band offsets of hole states within Si/Ge nanostructures reach about 400?meV. Typical quantization energies of about 40?meV due to lateral confinement and Coulomb charging energies up to about 15?meV were observed for holes confined in 20?nm sized Si/Ge dots. Future applications of Si/Ge nanostructures such as photodetectors with improved performance or novel functionality are discussed.
TL;DR: Photoluminescence measurements of a quasi-two-dimensional exciton gas in GaAs/AlGaAs coupled quantum wells and the observation of a macroscopically ordered exciton state are reported.
Abstract: There is a rich variety of quantum liquids—such as superconductors, liquid helium and atom Bose–Einstein condensates—that exhibit macroscopic coherence in the form of ordered arrays of vortices1,2,3,4. Experimental observation of a macroscopically ordered electronic state in semiconductors has, however, remained a challenging and relatively unexplored problem. A promising approach for the realization of such a state is to use excitons, bound pairs of electrons and holes that can form in semiconductor systems. At low densities, excitons are Bose-particles5, and at low temperatures, of the order of a few kelvin, excitons can form a quantum liquid—that is, a statistically degenerate Bose gas or even a Bose–Einstein condensate5,6,7. Here we report photoluminescence measurements of a quasi-two-dimensional exciton gas in GaAs/AlGaAs coupled quantum wells and the observation of a macroscopically ordered exciton state. Our spatially resolved measurements reveal fragmentation of the ring-shaped emission pattern into circular structures that form periodic arrays over lengths up to 1 mm.
TL;DR: In this article, a tetrapod-like zinc oxide (T-ZnO) nanorod was produced in bulk quantity by oxidation of Zn powders by a vapor-solid (VS) mechanism.
TL;DR: In this article, a solution of monodisperse nanocrystals with an absorption maximum at 537 nm was synthesized at 330 °C using TOPO (trioctylphosphineoxide) and TOP (tioctyl phosphine) as capping agents and Cd-acetate and Se powder as precursors.
Abstract: Electrogenerated chemiluminescence (ECL) was observed from TOPO-capped CdSe nanocrystals dissolved in CH2Cl2 containing 0.1 M TBAP. The solution of monodisperse nanocrystals with an absorption maximum at 537 nm was synthesized at 330 °C using TOPO (trioctylphosphineoxide) and TOP (trioctylphosphine) as capping agents and Cd-acetate and Se powder as precursors. The photoluminescence (PL) spectrum showed an emission maximum at 545 nm. Cyclic voltammetry and differential pulse voltammetry of this solution displayed no distinctive features, but light emission was observed through the annihilation of oxidized and reduced forms electrogenerated during cyclic potential scans or steps. The oxidized species was somewhat more stable than the reduced form. The ECL spectrum was substantially red shifted by ∼200 nm from the PL spectrum, suggesting that surface states play an important role in the emission process.
Abstract: Trivalent-rare-earth ion-doped Y2O3 nanocrystals have been synthesized, and their photoluminescence properties have been studied under 980 nm laser diode excitation. The crystallite size estimated by x-ray diffractometry and scanning electron microscopy was about 30–40 nm. In Yb3+ and Tm3+ codoped Y2O3 nanocrystals, the bright blue emissions near 450 and 480 nm have been noticeable due to the 1D2–3F4 and 1G4–3H6 transitions of Tm3+, respectively. The bright green emissions of Er3+ doped Y2O3 nanocrystals appeared near 530 and 550 nm were assigned to the 2H11/2–4I15/2 and 4S3/2–4I15/2 transitions of Er3+, respectively. The ratio of the intensity of green luminescence to that of red luminescence has decreased with an increase of concentration of Yb3+ in Er3+ doped Y2O3 nanocrystals. In sufficient quantities of Yb3+ to Er3+, the bright red emission near 660 nm has been predominant due to the 4F9/2–4I15/2 transition of Er3+. The primary color components are in these red, green, and blue emissions, from which ...
TL;DR: Inspired by experiments on atom condensation, and using specially designed semiconductor nanostructures, the photoluminescence measurements show that the quasi-two-dimensional excitons indeed condense at the bottom of the traps, giving rise to a statistically degenerate Bose gas.
Abstract: An exciton is an electron-hole bound pair in a semiconductor. In the low-density limit, it is a composite Bose quasi-particle, akin to the hydrogen atom. Just as in dilute atomic gases, reducing the temperature or increasing the exciton density increases the occupation numbers of the low-energy states leading to quantum degeneracy and eventually to Bose-Einstein condensation (BEC). Because the exciton mass is small--even smaller than the free electron mass--exciton BEC should occur at temperatures of about 1 K, many orders of magnitude higher than for atoms. However, it is in practice difficult to reach BEC conditions, as the temperature of excitons can considerably exceed that of the semiconductor lattice. The search for exciton BEC has concentrated on long-lived excitons: the exciton lifetime against electron-hole recombination therefore should exceed the characteristic timescale for the cooling of initially hot photo-generated excitons. Until now, all experiments on atom condensation were performed on atomic gases confined in the potential traps. Inspired by these experiments, and using specially designed semiconductor nanostructures, we have collected quasi-two-dimensional excitons in an in-plane potential trap. Our photoluminescence measurements show that the quasi-two-dimensional excitons indeed condense at the bottom of the traps, giving rise to a statistically degenerate Bose gas.
TL;DR: In this article, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size, and it was found that the photophotonicity follows very closely the quantum-confinement model.
Abstract: Silicon nanocrystals with diameters between 2.5 and 8 nm were prepared by pulsed CO2 laser pyrolysis of silane in a gas flow reactor and expanded through a conical nozzle into a high vacuum. Using a fast-spinning molecular-beam chopper, they were size-selectively deposited on dedicated quartz substrates. Finally, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size. It was found that the photoluminescence follows very closely the quantum-confinement model. The yield shows a pronounced maximum for sizes between 3 and 4 nm.
TL;DR: In this article, the recombination rate of spontaneous emission into the surface plasmon was as much as 92 times faster than spontaneous emission to free space, based on Fermi's golden rule.
Abstract: Using time-resolved photoluminescence measurements, the recombination rate in an ${\mathrm{In}}_{0.18}{\mathrm{Ga}}_{0.82}\mathrm{N}/\mathrm{GaN}$ quantum well (QW) is shown to be greatly enhanced when spontaneous emission is resonantly coupled to a silver surface plasmon. The rate of enhanced spontaneous emission into the surface plasmon was as much as 92 times faster than QW spontaneous emission into free space. A calculation, based on Fermi's golden rule, reveals that the enhancement is very sensitive to silver thickness and indicates even greater enhancements are possible for QW's placed closer to the surface metal coating.
TL;DR: In this paper, the steady state and transient dynamics of charged and neutral photoexcitations in thin films of poly-3-alkyl thiophene with regioregular order were studied.
Abstract: Using a variety of optical probe techniques we studied the steady state and transient dynamics of charged and neutral photoexcitations in thin films of poly-3-alkyl thiophene with regioregular order, which forms self-assembled lamellae structures with increased interchain interaction, as well as regiorandom order that keeps a chain-like morphology. In regiorandom polythiophene films we found that intrachain excitons with correlated photoinduced absorption and stimulated emission bands are the primary photoexcitations; they give rise to a moderately strong photoluminescence band, and long-lived triplet excitons and intrachain charged polarons. In regioregular polythiophene films, on the contrary we found that the primary photoexcitations are excitons with much larger interchain component; this results in lack of stimulated emission, vanishing intersystem crossing, and a very weak photoluminescence band. The long-lived photoexcitations in regioregular polythiophene films are interchain excitons and delocalized polarons (DP) within the lamellae, with very small relaxation energy. The characteristic properties of the DP species are thoroughly investigated as a function of the alkyl side group of the polymer backbone, film deposition conditions and solvents used, as well as at high hydrostatic pressure. The quantum interference between the low energy absorption band of the DP species and a series of photoinduced infrared active vibrations, which give rise to antiresonances that are superimposed on the electronic absorption band is studied and explained by a Fano-type interference mechanism, using the amplitude mode model.
TL;DR: In this article, the second and third-harmonic generation (SHG, THG) were imaged on single zinc oxide (ZnO) nanowires using near-field scanning optical microscopy (NSOM).
Abstract: The nonlinear optical response of semiconductor nanowires has potential application for frequency conversion in nanoscale optical circuitry. Here, second- and third-harmonic generation (SHG, THG) are imaged on single zinc oxide (ZnO) nanowires using near-field scanning optical microscopy (NSOM). The absolute magnitudes of the two independent (2) elements of a single wire are determined, and the nanowire SHG and THG emission patterns as a function of incident polarization are attributed to the hexagonal nanowire geometry and (2) tensor symmetry. Semiconductor nanowires are of current interest because of their unique electrical and optical properties. 1-3 In particular, their nonlinear optical properties suggest potential applications as frequency converters or logic/routing elements in nanoscale optoelectronic circuitry. A linear optical property of nanowires, photoluminescence (PL) polarization, has recently been studied in single indium phosphide nanowires. 2 In that case, the PL polarization is based upon the classical electromagnetic properties of a dielectric cylinder and averages ca. 91%. In contrast, coherent nonlinear optical phenomena, such as second- and third-harmonic generation (SHG and THG, respectively), depend explicitly on the crystal lattice structure of the medium, which could yield a very high (nearly 100%) polarization selectivity. In addition, the temporal response of the nonresonant harmonic generation is similar to the pulse width of the pump laser, in some cases 20 fs, 4 while incoherent processes are at least 2-4 orders of magnitude slower. Moreover, nonresonant SHG is essentially independent of wavelength below the energy band gap of semiconductor materials, most often including the 1.3-1.5 Im wavelength region typically used in optical fiber
TL;DR: In this article, the photoluminescence (PL) lifetimes in nanostructured silicon are typically very long−approximately 3 orders of magnitude longer than those of direct band gap semiconductors.
Abstract: Quantum confinement in nanostructured silicon can lead to efficient light emission. However, the photoluminescence (PL) lifetimes in nanostructured silicon are typically very long−approximately 3 orders of magnitude longer than those of direct band gap semiconductors. Herein, we show that organic monolayer coated silicon nanocrystals ranging from 1 to 10 nm in diameter emit with nanosecond-scale lifetimes and high quantum yields, making it possible to measure the PL spectra of single Si quantum dots. The Si quantum dots demonstrate stochastic single-step “blinking” behavior and size-dependent PL spectra with line widths approximately only three times greater than those measured for CdSe nanocrystals at room temperature.
TL;DR: The structure of ZnO quantum dots prepared via the wet chemical method was studied in this article, and the effect of the change in the structure of the dots on their luminescence properties was investigated.
Abstract: The structure of ZnO quantum dots prepared via the wet chemical method was studied. By introducing an annealing treatment (150 °C–500 °C), we also investigated the effect of the change in the structure of the dots on their luminescence properties. Our studies revealed that the surface of the as-prepared dots is passivated by a thin layer of Zn(OH)2, thus, the dots consist of a ZnO/Zn(OH)2 core-shell structure. We present evidence that the weak excitonic transition of ZnO quantum dots is strongly correlated with the presence of the surface shell of Zn(OH)2. When Zn(OH)2 is present, the excitonic transition is quenched.
TL;DR: In this paper, a simple chemical reduction route at room temperature is described to synthesize nanocrystalline CdS, ZnS, and CdxZn1-xS.
Abstract: A novel and simple chemical reduction route at room temperature is described to synthesize nanocrystalline CdS, ZnS, and CdxZn1-xS. In the method, anhydrous CdCl2, or ZnCl2, S, and KBH4 powders react at room temperature in various organic solvents, and the effect of the solvent on the quality of the nanoparticle product is investigated. Among the solvents used, tetrahydrofuran is shown to produce the highest quality single-phase nanoparticles. The nanoparticles are characterized by X-ray diffraction, transmission electron microscopy, UV−vis absorption, and photoluminescence. The particle size ranges from 4 to 8 nm. In the CdxZn1-xS, the lattice structure gradually changes from cubic to hexagonal with increasing percentage of Zn in the ternary compound CdxZn1-xS. The nanoparticles exhibit broad emission peaks that shift to shorter wavelength with increasing percentage of Zn in the ternary compound CdxZn1-xS. The control of the composition of CdxZn1-xS nanoparticles may lead to the development of ideal mate...
TL;DR: In this paper, the photoluminescence properties of synthesized single-crystal ZnS nanowires have been analyzed using high-resolution transmission electron microscopy (HRTEM).
TL;DR: In this article, a survey of optical absorption, photoluminescence and photomodulated reflectance spectra of single-crystalline hexagonal InN layers is presented.
Abstract: A survey of most recent studies of optical absorption, photoluminescence, photoluminescence excitation, and photomodulated reflectance spectra of single-crystalline hexagonal InN layers is presented. The samples studied were undoped n-type InN with electron concentrations between 6 × 10 18 and 4 × 10 19 cm -3 . It has been found that hexagonal InN is a narrow-gap semiconductor with a band gap of about 0.7 eV, which is much lower than the band gap cited in the literature. We also describe optical investigations of In-rich In x Ga 1-x N alloy layers (0.36 < x < 1) which have shown that the bowing parameter of b ∼ 2.5 eV allows one to reconcile our results and the literature data for the band gap of In x Ga 1-x N alloys over the entire composition region. Special attention is paid to the effects of post-growth treatment of InN crystals. It is shown that annealing in vacuum leads to a decrease in electron concentration and considerable homogenization of the optical characteristics of InN samples. At the same time, annealing in an oxygen atmosphere leads to formation of optically transparent alloys of InN-In 2 O 3 type, the band gap of which reaches approximately 2 eV at an oxygen concentration of about 20%. It is evident from photoluminescence spectra that the samples saturated partially by oxygen still contain fragments of InN of mesoscopic size.
TL;DR: In this paper, a spin-coating technique was used to construct thin films of microcrystalline CH3NH3PbX3 and their mixed-halide crystals, and their optical properties were investigated.
Abstract: Thin films of microcrystalline CH3NH3PbX3 (X = halogen) as well as their mixed-halide crystals were fabricated by the spin-coating technique, and their optical properties were investigated. X-ray diffraction investigation revealed that CH3NH3PbBr3 − x
Cl
x
(x = 0–3) were successfully formed on glass substrate self-assembly and oriented with the a-axis. Owing to due to their large exciton binding energy, these materials showed clear exciton absorption and free-exciton emission in the visible region at room temperature. Replacing Br with CI made it possible to control the band structure of these materials. As a result, the peak position of the exciton band shifted continuously towards blue region with increasing the CI content in the films.
TL;DR: In this paper, a commercial spectrofluorimeter can be used successfully in combination with an integrating sphere to measure solid-state photoluminescence quantum yields of films.
Abstract: In this article we show that a commercial spectrofluorimeter can be used successfully in combination with an integrating sphere to measure solid-state photoluminescence quantum yields of films. This approach significantly simplifies the experimental method as the need for specialized equipment on the excitation and detection side is relaxed. Two different light-emitting polymer systems are examined with this approach, and the results agree with those that have been reported previously using different methods.