Search

All inorganic CsPbBr3 perovskite quantum dots (QDs) are potential emitters for electroluminescent display. We demonstrated an easy hot-injection method to partially replace the toxic Pb2+ with the highly stable Sn4+. Meanwhile, the absolute photoluminescence (PL) quantum yield of CsPb1-xSnxBr3 with Sn(IV) substitution increased from 45% to 83%. Based on femtosecond transient-absorption (TA), time-resolved PL, and single-dot spectroscopies, TA dynamics in undoped CsPbBr3 and CsPb0.67Sn0.33Br3 QDs at various excitation fluences., providing a clear evidence for the suppression of trion generation. These highly luminescent CsPb0.67Sn0.33Br3 QDs exhibit emission wavelength of 517 nm. The highest device performance exhibited a luminescence of 12,500 cd/m2, a current efficiency (CE) of 11.63 cd/A, an external quantum efficiency (EQE) of 4.13%, a power efficiency (PE) of 6.76 lm/w, and a low turn-on voltage of 3.6 V, which are the highest values among reported Sn-based perovskite QLEDs.

All inorganic CsPbBr3 perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot-injection method to partially replace the toxic Pb2+ with highly stable Sn4+ . Meanwhile, the absolute photoluminescence quantum yield of CsPb1-x Snx Br3 increased from 45 % to 83 % with SnIV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr3 and CsPb0.67 Sn0.33 Br3 QDs at various excitation fluences were determined by femtosecond transient absorption, time-resolved photoluminescence, and single-dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb0.67 Sn0.33 Br3 QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m-2 , a current efficiency of 11.63 cd A-1 , an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w-1 , and a low turn-on voltage of 3.6 V, which are the best values among reported tin-based perovskite quantum-dot LEDs.

We characterize the radiation-induced damage of InGaP/GaAs/Ge solar cells for various proton irradiation energies and fluences using conventional current-voltage (I-V) measurements, external quantum efficiency, and a noncontact time-resolved photoluminescence (PL) technique. From the I-V curves, we obtain the conversion efficiency of the entire device. The external quantum efficiency showed that the short-circuit current is only determined by the top InGaP subcell. To obtain accurate information about the point of maximum power, a new PL technique is introduced. The PL time decays of the InGaP and GaAs subcells are measured to obtain the characteristic decay time constants of carrier separation and recombination. We empirically verify that the time-resolved PL method can be used to predict the electrical conversion efficiency of the subcells. We find that the limiting subcell at the point of maximum power is different from that for short-circuit current. Radiation damage in unexpected regions of the device is revealed using this optical method.

Giant-shell CdSe/CdS core/shell nanocrystals have attracted much attention due to their unique quasi-type-II band alignment, where a large valence band offset confines holes strongly to the core but electrons are delocalized due to a small conduction band offset. Here, we report the observation of the relative enhancement in the radiative recombination rate of a biexciton compared to that of an exciton in giant-shell CdSe/CdS nanocrystals. We found a clear correlation between the shell thickness of the CdSe/CdS nanocrystals and the ratio between the radiative recombination rates of the biexciton and exciton. Our finding can be explained by a picture in which the biexciton emission efficiency is enhanced through electron localization around the core due to the strong Coulomb potential of the two holes confined in the core.

The realization of high-quality quantum emitters that can operate at room temperature is important for accelerating the application of quantum technologies, such as quantum communication, quantum information processing, and quantum metrology. In this work, we study the photon-antibunching properties on room-temperature emission from individual colloidal quantum dots (CQDs) using superconducting-nanowire single-photon detectors and temporal filtering of the photoluminescence decay curve. We find that high single-photon purities and high photon-generation rates can be simultaneously achieved by removing the signals originating from the sequential two-photon emission of biexcitons created by multiple excitation pulses. We successfully demonstrate that the ultrahigh performance of the room-temperature single-photon sources showing g(2)(0) ≪ 10−2 can be confirmed by the ultralow-dark-count detection of the temporally purified single photons. These findings provide strong evidence for the attractiveness of CQDs as candidates for high-quality room-temperature quantum light sources.

Metal–halide perovskite nanocrystals (NCs) are promising photonic materials for use in solar cells, light-emitting diodes, and lasers. The optoelectronic properties of these devices are determined by the excitons and exciton complexes confined in their NCs. In this study, we determined the relaxation dynamics of charged excitons and biexcitons in CsPbBr3 NCs using femtosecond transient-absorption (TA), time-resolved photoluminescence (PL), and single-dot second-order photon correlation spectroscopy. Decay times of ∼40 and ∼200 ps were obtained from the TA and PL decay curves for biexcitons and charged excitons, respectively, in NCs with an average edge length of 7.7 nm. The existence of charged excitons even under weak photoexcitation was confirmed by the second-order photon correlation measurements. We found that charged excitons play a dominant role in luminescence processes of CsPbBr3 NCs. Combining different spectroscopic techniques enabled us to clarify the dynamical behaviors of excitons, charged ex...

The temporal fluctuations in the photoluminescence (PL) spectra of single CdSe/ZnS nanocrystals (NCs) exhibiting PL blinking at room temperature as well as their dynamical properties were studied. In the case of large NCs, measuring the time-dependent PL intensities and lifetimes allowed us to separately characterize the degree of spectral diffusion (SD) of the exciton and trion (charged exciton) emissions. The SD properties, such as the polarizability and field fluctuation, were investigated quantitatively through comparisons with the results of numerical calculations based on a simple field fluctuation model. We found that trion emissions exhibit unique SD characteristics; i.e., their binding energies are positive and their polarizabilities are smaller than those of excitons. In addition, we observed that the exciton emissions exhibited size-dependent SD behaviors, reflecting the differences in the polarizabilities of the NCs with different sizes. Finally, the experimental data, including an analysis of...

Colloidal quantum dots (CQDs) are attractive material for single-photon sources (SPSs) that can be utilized at room temperature. In this work, we performed simultaneous measurements of photoluminescence (PL) decay curve and second-order photon correlation, g(2), on single CQDs to study the purity of their single photons, which is determined by the value of g(2)at the time origin. We demonstrate that the single-photon purity can be improved through time-gated g(2) analysis, where a part of the PL signal is excluded by applying a temporal filter to the PL decay curve. We show that by using a superconducting nanowire single-photon detector, it is possible to observe highly-purified single photons that exhibited g(2) at the time origin ranging from 0.01 to 0.02.

Transition metal dichalcogenide represented by molybdenum disulfide (MoS2) is a promising platform for versatile applications in biosensing. The semiconducting properties of MoS2 coupled with its large surface area allows for highly sensitive detection of external environments. Although chemical vapor deposition (CVD) is a promising method for synthesizing large and high quality MoS2, optical properties of CVD-grown MoS2 under physiological solution is not clear. Furthermore, understanding of the pH effect on its optical properties is still limited. Here, we report their photoluminescence (PL) responses to solution pH under aqueous condition by means of PL spectroscopy and imaging. MoS2 with different Mo sources and additive such as MoS2, MoO2 and NaCl were synthesized. It was found that the PL response was highly affected by the Mo sources. While MoS2 made from MoO2 showed the highest modulation of PL by solution pH, MoS2 made from MoS2 did not show significant response. Furthermore, we demonstrated enhanced pH-sensitivity by UV/O3 treatments. Spectral analysis on PL and X-ray photoelectron spectroscopy revealed that the PL responses to solution pH were not directly correlated to the defect density (S/Mo ratio) of MoS2, but likely correlated to its state of defects and initial carrier density. These findings will be a practical guideline to optimize synthesis condition toward developing MoS2-based optoelectronic biosensing devices.

The photoluminescence (PL) lifetime and quantum yield (QY) of the two-photon cascade emission (TPCE) provide critical information for assessing the quality of optoelectronic devices. The QY of TPCE has been conventionally evaluated by second-order photon correlation, ${g}^{(2)}$, measurements under weak-excitation conditions in single nanocrystals (NCs). Here, we report that by measuring simultaneously both the ${g}^{(2)}$ and PL-decay curves, the QY of the TPCE can be determined even under strong-excitation conditions. With this technique, the effect of ionization on the QY of the TPCEs in single CdSe/ZnS NCs, which appears under strong-excitation condition, can be revealed. The obtained QYs were compared with the PL lifetime of the first and second photon emissions. We demonstrate that even for ionized NCs, the radiative recombination rates during TPCE are almost proportional to the product of the numbers of electrons and holes.

Recently, metal-halide perovskite semiconductors have been extensively studied because of their potential use in solar-cell, photodetector, light-emitting-diode, and laser applications. In particular, perovskite nanocrystals (NCs) are gaining more and more attention because their optical spectra can be manipulated by changing the NC size and the halogen composition [1]. In contrast to the conventionally structured NCs such as colloidal CdSe NCs, high-quality perovskite NCs with unique cubic shapes and large sizes can be fabricated. However, their intrinsic photocarrier recombination dynamics have not yet been understood. Especially, the recombination dynamics of exciton complexes including biexcitons and charged excitons (trions) are complicated due to the fast Auger recombination [2]. Thus, a combination of different optical techniques for ensemble and single NC samples should be performed for a deep understanding of multiexciton dynamics in perovskites.

Metal-halide perovskite nanocrystals (NCs) are promising photonic materials for use in solar cells, light-emitting diodes, and lasers. The optoelectronic properties of these devices are determined by the excitons and exciton complexes confined in their NCs. In this study, we determined the relaxation dynamics of charged excitons and biexcitons in CsPbBr

Charge carrier dynamics in perovskite CH3NH3PbI3 solar cells were studied by means of microscopic photoluminescence (PL) and photocurrent (PC) imaging spectroscopy. The PL intensity, PL lifetime, and PC intensity varied spatially on the order of several tens of micrometers. Simultaneous PL and PC image measurements revealed a positive correlation between the PL intensity and PL lifetime, and a negative correlation between PL and PC intensities. These correlations were due to the competition between photocarrier injection from the CH3NH3PbI3 layer into the charge transport layer and photocarrier recombination within the CH3NH3PbI3 layer. Furthermore, we found that the decrease in the carrier injection efficiency under prolonged light illumination leads to a reduction in PC, resulting in light-induced degradation of solar cell devices. Our findings provide important insights for understanding carrier injection at the interface and light-induced degradation in perovskite solar cells.

The sequential two-photon emission process known as biexciton cascade emission is a characteristic phenomenon that occurs in photoexcited semiconductor nanocrystals (NCs). This process occurs when a biexciton state is created in the NCs; thus, the occurrence of the process is related to the photoabsorption properties of the NCs. This paper presents a simple equation that connects the photoabsorption of single NCs and the biexciton cascade emission. The equation is found to be independent of the quantum yields of photoluminescence (PL). With this equation and using an analysis of second-order photon correlation, the absolute absorption cross section $\ensuremath{\sigma}$ of the single NCs can be evaluated, obtaining values on the order of ${10}^{\ensuremath{-}14}\phantom{\rule{4pt}{0ex}}\mathrm{c}{\mathrm{m}}^{2}$. This analysis shows that ionization during PL blinking does not affect the validity of the relation, indicating that the evaluation of $\ensuremath{\sigma}$, based on the equation, is applicable for various NCs with unique structures.

Micro-photoluminescence (PL) and micro-PL excitation (PLE) spectra were measured systematically in a 5 nm GaAs/AlAs single quantum well (QW) to investigate the predicted effect of asymmetric exciton absorption line shapes having high-energy tails due to weak localization of exciton center-of-mass motion by interface roughness. We found a characteristic change in the asymmetric shapes as the QW-interface coverage by monolayer terraces varied. Via spectral fitting using a reported model, we quantitatively obtained a localization length varying between 4–15 nm, and verified the validity as well as limitation of this model.

We studied time-dependent fluctuations of photoluminescence (PL) spectra of single CdSe/ZnS nanocrystals (NCs), which show PL blinking and spectral diffusion. We observed correlations between PL peak energy, intensity, and linewidth, which are due to the quantum confined Stark effect. We found that a characteristic asymmetric shape appears in the PL peak energy histogram, which can be explained by a simple field-fluctuation model. By comparing the experimental results with theoretical calculations, we evaluate the mean value and standard deviation of the fluctuating electric field. We discuss the experimental data using a model considering a few elementary charges around the NCs, which are the origin of the field fluctuation.

The absorption spectrum represents an important aspect of single semiconductor nanocrystals (NCs), revealing the morphology and orientation of the NCs. By conducting quantitative photoluminescence excitation spectroscopy based on a single-photon counting method, we succeed in clarifying the absorption cross-section spectrum of neutral excitons in single CdSe/ZnS NCs. With the values of the absorption cross section, we reveal that the intensity saturation of the neutral-exciton emission can be explained by considering the Poisson statistics for incident photons and by the small quantum yield of the biexciton emission. We also evaluated quantitatively the biexciton emission contribution and the ionization rate of NCs that appear at increased incident photon fluxes.

Time-resolved photoluminescence (PL) is very useful for analyzing carrier dynamics and electrical properties of subcells which cannot be contacted directly. We investigate the excitation spot-size dependence of the PL decay time constants which are observed at high excitation powers. The excitation spot-size dependence is approximately linear and almost the same for both time constants. The origin of the spot-size dependence and the method for obtaining the subcell carrier-collection efficiencies are discussed.

Photoluminescence (PL) fluctuations of single semiconductor nanocrystals (NCs), such as PL blinking and spectral diffusion (SD), reflect the quantum nature of charges in the NCs. Through simultaneous measurements of PL spectra and lifetimes on single CdSe/ZnS NCs, PL of neutral excitons is found to exhibit a unique behavior of SD, which is accompanied by changes of radiative recombination lifetime. We find that the SD of neutral excitons originated from the quantum-confined Stark effect, which also affects the SD of charged excitons observed during PL blinking.

CdSe/CdS heterostructured nanocrystals with quasi-type-II band alignments provide an interesting platform for studying the photoluminescence (PL) blinking associated with their unique morphologies. By using simultaneous measurements of the PL intensity, lifetime, and polarization anisotropy, we reveal the role of the electron delocalization during the blinking of single CdSe/CdS dot-in-rods. We found that a significant change in the PL polarization anisotropy distinguishes between two kinds of charged excitons with different electron delocalizations. We report our observation of unique polarized PL blinking governed by the band alignments and the Coulomb interactions between the charges inside and outside the dot-in-rod.

Carrier-density dependence of the optical-gain spectra were studied for an undoped T-shaped quantum-wire (T wire) laser by optical pumping at 4 K. The gain appeared at a low excitation power of 3 mW corresponding to the carrier density of about 3 × 105 cm–1 in the T wire. As the carrier density was increased, the peak gain increased, but it reached a maximum value of about 1 × 104 cm–1 at the carrier density of 1 × 106 cm–1 and then decreased hereafter. This peculiar gain evolution dependent on the carrier density was not explained by a simple free-electron model, which suggests significant contributions of the enhanced Coulomb interactions to the optical gain in the T-wire laser. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Microscopic photoluminescence images were measured on a dilute two-dimensional electron gas (2DEG) in an n-type modulation doped quantum well at 5 K. We observed electron-depletion regions surrounding metal electrodes formed by annealing of soldered indium or evaporated AuGeNi. The difficulty of forming an ohmic contact to a dilute 2DEG was probably due to the depletion region separating the 2DEG from the metal electrode.

We measured the cavity length dependence of the internal differential quantum efficiency ηint and the internal optical loss αint in 1500-nm-wavelength laser diodes (LDs). By evaluating αint directly from gain/absorption spectra for various injection current densities and measuring the external differential quantum efficiency ηext, we obtained the ηint and αint values of all the LDs with different cavity lengths. The obtained ηint and αint respectively showed strong and weak cavity length dependences, and were both very different from those derived by the widely used method of plotting ηext-1 against the cavity length.

A one-dimensional active region consisting of 20-period T-shaped GaAs/AlGaAs quantum wires of 14×6 nm2 combined with a well-defined current-confinement scheme has been utilized to obtain a low-threshold-current high-efficiency laser. A threshold current as low as 0.27 mA, a single-mode cw output power of 0.13 mW at 1 mA injection current, and a differential quantum efficiency of 12% were achieved at 30 K using a quantum-wire laser with a 500-µm-long Fabry–Perot cavity coated by high-reflectivity thin metals.

We performed microscopic imaging of photoluminescence (PL) and photocurrent (PC) on InAs nanostructures including disklike structures (nanodisks) and quantum dots (QDs). The correlation between PL and PC images indicates that the major fraction of upconverted carriers originates from nanodisks. By analyzing the excitation spectra, we find evidence that nanodisks and QDs need to be spatially separated to enhance PC generation via upconversion. The efficient simultaneous use of both QDs and nanodisks is an alternative approach to intermediate-band solar cells, where low-energy photons are upconverted in the QDs and high-energy photons are efficiently upconverted in the nanodisks, resulting in enhanced carrier generation yields. With spatially resolved upconverted PL, we show that PC generation in nanodisks is due to ejection of both electrons and holes.

The excitation density dependence of photoluminescence (PL) blinking of single CdSe/ZnS quantum dots was studied by means of single-dot PL spectroscopy. As the excitation density increases, an intermediate state appears in addition to the highly emissive (ON) and nonemissive (OFF) states. The systematic study of the excitation density dependence of PL blinking behavior (PL intensity, probabilities of finding these states, time probability distributions, and PL spectra and lifetimes) suggests that the intermediate state can be attributed to a charged exciton (trion) state generated through biexciton generation and charging (ionization) of a quantum dot under a high-density excitation regime. Our results indicate that the biexciton generation is a precursor of the trion state and not of the OFF state.

We present theoretical and experimental studies of the amplitude of the terahertz (THz) light emitted by biased superlattices excited by fast optical pulses as a function of the pump photon energy. The comparison of the measured transient signal and of its dependence upon the excitation photon energy with a model calculation allows a clear separation between the contributions of the dissociated carriers and bound pairs to the emitted THz field.

We have systematically investigated the time-evolution of transient electron transport in semiconductor superlattices (SLs) under dc electric fields for various initial electron distributions created by femtosecond laser pulses. It is found that the terahertz (THz) waveforms are very insensitive to the pump photon energy and that the transient current starts from its maximum as damped cosω B t. We will show that the unique electron distribution under WS localization of electron wave functions in the translational symmetry is essential for the observed phase of the photoinduced current. Furthermore, as a first step toward realization of Bloch oscillators, a preliminary result on the effects of planar photonic crystal electrode on the THz emission will be briefly presented.

Gain characteristics of optically-excited semiconductor quantum wires are studied theoretically and experimentally at various carrier densities to clarify the correlation effects in electron-hole plasma. The profiles of gain spectra are significantly modified by the Coulomb interactions, by which serious suppression of peak gain occurs at high carrier densities.

CW single-mode lasing from 30 K to 70 K with the lowest threshold current of 0.27 mA has been demonstrated in 20-period T-shaped quantum-wire laser diodes with parallel p and n doping layers.

Variable-density one-dimensional electron gas was realized in a T-shaped quantum wire with an FET gate. We achieved photoluminescence-excitation measurements on a single wire and observed spectral evolution from degenerate to non-degenerate one-dimensional electron gas.

Conventional external quantum-efficiency measurement of solar cells provides charge-collection efficiency for approximate short-circuit conditions. Because this differs from actual operating voltages, the optimization of high-quality tandem solar cells is especially complicated. Here, we propose a contactless method, which allows for the determination of the voltage dependence of charge-collection efficiency for each subcell independently. By investigating the power dependence of photoluminescence decays, charge-separation and recombination-loss time constants are obtained. The upper limit of the charge-collection efficiencies at the operating points is then obtained by applying the uniform field model. This technique may complement electrical characterization of the voltage dependence of charge collection, since subcells are directly accessible.

Semiconducting nanocrystal quantum dot (QD) films with high multiple exciton generation (MEG) efficiencies and high exciton dissociation efficiencies are appealing as solar cell materials. Here, we report the strong enhancement of the photocurrent in close-packed QD films, and discuss the importance of surface ligands on MEG and charge transport in QD films. Both exciton-recombination and charge-transport properties are influenced by the phenomenon of carrier tunnelling between neighboring QDs in thin films. These results can have important implications in the design of chemical treatments to control the electronic interactions between QDs in solution-processed solar cells. We demonstrate that the inorganic- and small sized-ligand passivation of PbS QDs by potassium thiocyanate causes a significant photocurrent enhancement.

We demonstrated a new method of radiation thermometry at cryogenic temperatures on the basis of the detailed balance relation between absorption and photoluminescence in a small n-type-modulation-doped GaAs quantum-well sample. This method has unique advantages such as being non invasive. It also does not need to be calibrated and possibly offers high spatial resolution. We measured temperatures of a sample mounted on a sapphire substrate attached to a copper cold finger at 7–101 K in a cryostat. The temperatures measured with this method were consistent with those obtained from a separate calibrated traditional temperature sensor. The estimated uncertainties were ±2 K below 50 K and ±8 K below 100 K.

An absorption-spectroscopy method that utilizes internal emissions as the source of the probe light was used to measure the absorption spectra of quasi-one-dimensional (q-1D) excitons in T-shaped quantum wires embedded in an optical waveguide. The modal absorption area of the 1D ground-state excitons was estimated to be 0.39 eV cm−1 and was almost independent of temperature in the range 4–150 K. Quantitative evaluation using the absorption spectra revealed that the absorption cross-section per unit length at resonance peak and the spectrally integrated absorption cross-section area per unit length of the 1D ground-state excitons were 1.0 nm and 2.5 × 10−3 eV nm, respectively.

We have investigated the terahertz (THz) emission from a semiconductor superlattice placed in a waveguide structure with a photonic crystal surface electrode of a honeycomb lattice pattern. For uniformly applying bias voltages, we inserted a semitransparent Ti film between the superlattice layer and the photonic crystal electrode. It is found that optimization of the sheet resistivity of the Ti layer is crucial to suppress the coupling between the waveguide mode and the surface leaky mode and obtain a clear photonic band gap. When the Ti layer was 40 nm, a large extinction ratio of ∼120 in the THz emission intensity was obtained at the midgap frequency around 1.7 THz.

We report on the electronic structure, efficient carrier injection, and quantitative lasing characteristics of T-shaped GaAs/AlGaAs quantum-wire-laser diodes with parallel p- and n-doping layers grown by a cleaved-edge-overgrowth method with molecular-beam epitaxy. Continuous single-mode lasing from the ground subband of the quantum wires was demonstrated between 30 and 70 K in laser diodes with high-reflectivity Au coating on both cavity facets. The lowest threshold of 0.27 mA and the highest differential quantum efficiency of 12% were achieved at 30 K. Micro-photoluminescence measurements demonstrated the high optical quality of the quantum wires with narrow linewidth of 0.9 meV and provided electronic structures of surrounding layers. Microscopic electroluminescence (EL) imaging measurements demonstrated the efficient carrier injection into the quantum wires at 30 K. These two factors, i.e., high material quality and efficient carrier injection, contribute to the low threshold current and high efficien...

The authors measured the temperature dependence of the lasing properties of current-injection T-shaped GaAs∕AlGaAs quantum-wire (T-wire) lasers with perpendicular p- and n-doping layers. The T-wire lasers with high-reflectivity coatings on both cleaved facets achieved continuous-wave single-mode operation between 5 and 110K. The lowest threshold current was 2.1mA at 100K. The temperature dependences of differential quantum efficiency and threshold current were attributed mainly to that of current-injection efficiency.

One of the most important problems in the design of the thickness vibration resonator is how to suppress the anharmonic higher-order spurious mode which is generated near the main resonant frequency. It is easy to realize a single resonant characteristic by the design based on the trapped energy theory, but the area of the electrode and, consequently, the inductance, are limited. This paper proposes a method which improves this point and increases the degrees of freedom in the design, suppressing the anharmonic spurious mode by adding a mass to the edge of the electrode and by cancelling the charge. In other words, a modified circular electrode structure is proposed in which the peripheral part (ring) of the electrode has a larger thickness. The third overtone resonator is analyzed in detail, and it is shown theoretically that the dominant (3, 3, 1) spurious mode is suppressed by the charge cancellation, thereby realizing a resonator with an essentially single resonant characteristic over a wide frequency range. It is noted that the charge cancellation characteristics for the spurious mode are strongly dependent on the platebacking of the ring electrode. The data for the optimum design are summarized in a table which will be utilized in the future design.

We measured absorption spectra of T-shaped quantum wires at 5 K by laser-waveguide transmission experiment. The absorption coefficient at one-dimensional-exciton peak is 130 cm-1 and material absorption coefficient is 6times104 cm-1