Photoluminescence decay profiles of exciton‐exciton scattering in a ZnO thin film

Wakaiki, S.; Ichida, Hideki; Mizoguchi, K.; Kim, DaeGwi; Kanematsu, Yasuo; Nakayama, Masaaki

doi:10.1002/pssc.201000675

Cited by 9 publications

(20 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…23 It has been reported that the surface defect produces hydroxyl ions (OH -) when exposed to air. 24,25 In the current study the surface species and decrease in O vacancies caused a shift in the (002) diffraction peak to small 2θ values and reduced the c/a ratio. Decreases in O vacancies were also observed by the increased FWHM beyond 20 sccm.…”

mentioning

confidence: 56%

Significance of postgrowth processing of ZnO nanostructures on antibacterial activity against gram-positive and gram-negative bacteria

Mehmood¹,

Ismail²,

Mirza³

et al. 2015

IJN

View full text Add to dashboard Cite

In this work, we highlighted the effect of surface modifications of one-dimensional (1D) ZnO nanostructures (NSs) grown by the vapor–solid mechanism on their antibacterial activity. Two sets of ZnO NSs were modified separately – one set was modified by annealing in an Ar environment, and the second set was modified in O 2 plasma. Annealing in Ar below 800°C resulted in a compressed lattice, which was due to removal of Zn interstitials and increased O vacancies. Annealing above 1,000°C caused the formation of a new prominent phase, Zn 2 SiO 4 . Plasma oxidation of the ZnO NSs caused an expansion in the lattice due to the removal of O vacancies and incorporation of excess O. Photoluminescence (PL) spectroscopy was employed for the quantification of defects associated with Zn and O in the as-grown and processed ZnO NS. Two distinct bands were observed, one in the ultraviolet (UV) region, due to interband transitions, and other in the visible region, due to defects associated with Zn and O. PL confirmed the surface modification of ZnO NS, as substantial decrease in intensities of visible band was observed. Antibacterial activity of the modified ZnO NSs demonstrated that the surface modifications by Ar annealing limited the antibacterial characteristics of ZnO NS against Staphylococcus aureus . However, ZnO NSs annealed at 1,000°C or higher showed a remarkable antibacterial activity against Escherichia coli . O 2 plasma–treated NS showed appreciable antibacterial activity against both E. coli and S. aureus . The minimum inhibition concentration was determined to be 0.5 mg/mL and 1 mg/mL for Ar-annealed and plasma-oxidized ZnO NS, respectively. It was thus proved that the O content at the surface of the ZnO NS was crucial to tune the antibacterial activity against both selected gram-negative ( E. coli ) and gram-positive ( S. aureus ) bacterial species.

show abstract

mentioning

confidence: 56%

Significance of postgrowth processing of ZnO nanostructures on antibacterial activity against gram-positive and gram-negative bacteria

Mehmood¹,

Ismail²,

Mirza³

et al. 2015

IJN

View full text Add to dashboard Cite

show abstract

“…branch [4]. However, the value of fitting parameter A obtained from the data fitting of experimental results is much smaller than that calculated from the values of R and L of the ZnO thin film.…”

mentioning

confidence: 73%

“…The detail of the experimental set up for OKG method is reported in Ref. 4. Figure 1(a) and (b) shows the image plot of the time-resolved PL spectra in ZnO thin films with the film thickness of 200 and 500 nm, respectively.…”

mentioning

confidence: 99%

Slow propagation of photon-like polaritons generated by exciton-exciton scattering in ZnO thin films

Ichida

Wakaiki

Kawase

et al. 2013

EPJ Web of Conferences

View full text Add to dashboard Cite

Abstract. We report on the first observation of the thickness-dependent photoluminescence-decay time of exciton-exciton scattering in ZnO thin films, which indicates the slower propagation of photon-like polaritons compared to that in bulk by two orders magnitude.The intense emission caused by exciton-exciton scattering, which is called P emission, is an interesting subject from an aspect of ultrafast phenomena leading to stimulated emission. Another attractive aspect of the P emission is that it enables us to access the related photon-like polariton state that can lead to slowdown of light propagation [1]. In the inelastic scattering process of two excitons in the first quantum (n = 1) state, one exciton is scattered into a higher excited state with n ≥ 2, while the other exciton is scattered into a photon-like polariton state whose energy is lower than that of the n = 1 exciton state by the energy difference between the n = 1 and n ≥ 2 states [2]:where Ex(n,k) represents the exciton in n = i exciton state with a wavenumber of k. In the dynamical property of the exciton-exciton scattering, we have to take into account at least two processes on the basis of the exciton-polariton picture. First, in the exciton-exciton scattering process, the two exciton-polaritons are converted into a higher exciton and a photon-like polariton when the exciton density is higher than the threshold density. The rate of this collision process depends on the exciton density. The second process is the transformation of the polaritons into external photons on the crystal surface. The rate of this process is determined by [3] Here, vg is the group velocity of the polaritons and R and L are the reflection coefficient and the film thickness, respectively. From Eq. (2), the lifetime of photon-like polariton is proportional to the group-velocity dispersion of the photon-like polariton branch. In our previous work, we reported that the decay time of the P emission changes with the detection energy and the energy dependence of that could be reproduced directly from the group-velocity dispersion of the photon-like polariton EPJ Web of Conferences

show abstract

“…On the other hand, the problem can be simplified when we discuss the P emission. Since the emission frequency is far below the exciton resonance (e.g., about 0.1 eV for ZnO 21,23,24 ), even if the photon is reabsorbed, the created exciton emits a photon again without losing the memories of the phase and the propagation direction, i.e., the absorption coefficient is negligible at that frequency. Then, after the conversion from a localized exciton to a photon, we can consider simply the series of absorption and creation of a photon in the excitonic medium without the dephasing or scattering process.…”

Section: A Conversion Time From Exciton To Polaritonmentioning

confidence: 99%

“…22,26,27 Although these lifetimes basically depend on materials of samples, they are generally much shorter than the emission lifetime τ emit of bottleneck excitons at quasi-equilibrium (in the order of nanoseconds). The time-resolved measurements revealed also that the P-emission lifetime is an increasing function of the emission frequency, 20,21,[23][24][25]27 and the lifetime at each emission frequency is almost independent of the pumping power. 24,25 Note that the emissionfrequency-dependence of the P-emission lifetime can be scaled phenomenologically by that of inverse of the group velocity of the photon-like polariton.…”

mentioning

confidence: 99%

Theory of the lifetime of an exciton incoherently created below its resonance frequency by inelastic scattering

et al. 2015

Self Cite

View full text Add to dashboard Cite

When an exciton in semiconductor is scattered and its energy is decreased far below the resonance energy of the bare exciton state, it has been considered that an exciton-polariton is created immediately by the scattering process, because there is no exciton level at that energy. However, according to the recent time-resolved measurements of P emission originating from inelastic exciton-exciton scattering, it looks rather natural to consider that the exciton-polariton is created in a finite time scale which is restricted by a coherence volume of the exciton after the scattering. In this interpretation, the exciton remains in this time scale far below its resonance energy as a transient state in a series of processes. We propose an expression of the P-emission lifetime depending on the coherence volume of the scattered excitons through the conversion process from them to the polaritons. The coherence volume of the scattered excitons appears in the calculation of the inelastic scattering process on the assumption of a finite coherence volume of the bottleneck excitons. Time-resolved optical-gain measurements could be a way for investigating the validity of our interpretation.

show abstract

Photoluminescence decay profiles of exciton‐exciton scattering in a ZnO thin film

Cited by 9 publications

References 9 publications

Significance of postgrowth processing of ZnO nanostructures on antibacterial activity against gram-positive and gram-negative bacteria

Significance of postgrowth processing of ZnO nanostructures on antibacterial activity against gram-positive and gram-negative bacteria

Slow propagation of photon-like polaritons generated by exciton-exciton scattering in ZnO thin films

Theory of the lifetime of an exciton incoherently created below its resonance frequency by inelastic scattering

Contact Info

Product

Resources

About