Photoacoustic Spectra of CdInGaS 4 with a DC Electric Field

We report on the optical absorption properties, measured by the photoacoustic (PA) method, and photoelectrochemical current (PEC) characteristics (including transient measurements) of CdSe quantum dots (Q-dots) grafted onto a planar fluorine-doped SnO2 (FTO) substrate. CdSe Q-dots were fabricated by the chemical solution deposition (CD) technique. With increasing deposition time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots can be demonstrated. The average diameters of the CdSe Q-dots for each deposition time can be estimated using an effective mass approximation producing diameters of 5.1 nm to 5.6 nm for deposition times of 5 h to 25 h, respectively. Thus, PA spectroscopy is useful in obtaining the Q-dots sizes even though there is no use of a high-resolution scanning electron microscope (SEM). An increase in PEC and the clear shift of the spectra to the lower energy region are observed with increasing deposition time, indicating the photosensitization of the FTO electrodes in the visible region resulting from CdSe Q-dots. It can be seen that the maximum value of incident photon to current conversion efficiency (IPCE) is ∼10%, which is higher than that previously reported (∼6%). Transient PEC measurements show that electron recombination in a smaller amount of CdSe Q-dots is lower than that in a higher amount of Q-dots.

Section: Introductionmentioning

confidence: 99%

Photoacoustic and Photoelectrochemical Characterization of CdSe Quantum Dots Grafted onto Fluorine-Doped Tin Oxide (FTO) Substrate

Toyoda

Arae

Shen

2005

“…With this technique, for example, the band gap variation in lightly Co-doped ZnO can be estimated, 8) and the grain growth in the sintering process can also be monitored. 9) CoO is also used for ZnO varistors and very small amounts of Co-doped ZnO was also studied for use as varistors 10,11) and sintered semiconductors. 12) In this study, the PA techniques are applied to heavily Codoped ZnO powders.…”

Section: Introductionmentioning

confidence: 99%

Photoacoustic Spectra of Heavily Co-Doped ZnO Powders

Okamoto

Inoué

Kawahara

et al. 2005

Photoacoustic (PA) spectra were measured for heavily Co-doped ZnO powders using a microphone at room temperature. In PA spectra, the PA signal peaks of Co2+ and Co3+ can be observed with the ZnO band-gap signals. The two PA peaks related to Co ions show the Co valency change induced by the sintering, and depend on the sintering temperature and the Co concentration. For the heavily Co-doped samples, the Co valency conversion occurred at a low sintering temperature. PA spectroscopy has potential for estimating the inner ion state change during the sintering process.

“…The theory of interband optical absorption shows that at the absorption edge the optical absorption coefficient hν varies with the photon energy hν according to the expression characterization of electronic, optical, defect structures and thermal properties of materials is important because it yields direct information on nonradiative de-excitation energy channels. [14][15][16][17] …”

Section: Introductionmentioning

confidence: 99%

Characterization of Electronic States of TiO₂ Powders by Photoacoustic Spectroscopy

Toyoda¹,

Kawano²,

Shen³

et al. 2000

Self Cite

We have measured the optical absorption of TiO 2 powders by photoacoustic (PA) spectroscopy, which is powerful for detecting small amounts of strongly scattering materials. The band-gap energies E g of rutile and anatase types of TiO 2 powders with particle radii of 40 nm are 3.06 eV and 3.20 eV, respectively, from PA intensity and PA phase spectra, indicating the usefulness of PA spectroscopy. The PA intensity and phase spectra show that the E g of anatase-type TiO 2 powders with a particle radius of 11 nm is 3.25 eV (blue shift) within the experimental accuracy, indicating the possible onset of a quantum size effect with decreasing particle size. The PA intensities plotted semilogarithmically vary linearly with photon energy immediately below the band-gap, in accordance with Urbach's rule (exponential tail). The slope of the exponential absorption of rutile-type TiO 2 powders is larger than that of the anatase, indicating that the anatase-type has increasing energy from the displacement of atoms specifically due to oxygen vacancies and/or chlorine impurities in the production processes of the powders.KEYWORDS: rutile-type TiO 2 powder, anatase-type TiO 2 powder, photoacoustic intensity spectroscopy, photoacoustic phase spectroscopy, optical absorption spectroscopy, exponential optical absorption, quantum size effect 3160