R. Aga

Enhanced photoresponse in ZnO nanowires decorated with CdTe quantum dot

The photoresponse of ZnO nanowires irradiated with photons having energies below the band gap of ZnO (3.4eV) was studied before and after deposition of CdTe quantum dots via a pulsed electron-beam technique. The small amount of deposited CdTe did not increase the dark current of the samples. However, a substantial increase in the steady state photocurrent was observed after CdTe deposition suggesting a clear photosensitization effect. Results revealed that CdTe influences the photoconductivity transients of ZnO by minimizing its interaction with oxygen in air as well as providing additional traps that serve to increase the photocurrent time constant.

Er-doped ZnO films grown by pulsed e-beam deposition

Erbium (Er)-doped ZnO thin films were grown on fused silica (SiO2) substrates by pulsed electron-beam deposition (PED) and analysed by Rutherford backscattering spectrometry (RBS), ultraviolet–visible absorption, and photoluminescence (PL). Subsequent annealing at 700 °C produces remarkable effects on the optical properties of Er-doped films. Under 325 nm excitation, a dramatic increase of deep-level emission from 450 to 680 nm was observed from annealed Er-doped ZnO films. Under 488 nm excitation, the PL spectrum of annealed Er-doped ZnO films revealed sharp and well-resolved Stark-splitting peaks in both the green emission of transition and the red emission of transition of Er3+ ions, which suggests that the Er ions have been incorporated inside the crystalline ZnO grains after thermal annealing.

Increased short circuit current in organic photovoltaic using high-surface area electrode based on ZnO nanowires decorated with CdTe quantum dots

A photosensitized high-surface area transparent electrode has been employed to increase the short circuit current of a photovoltaic device with a blend of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM) as the active layer. This is achieved by directly growing ZnO nanowires on indium tin oxide (ITO) film via a physical vapor method. The nanowire surface is then decorated with CdTe quantum dots by pulsed electron-beam deposition (PED). The nanowires alone provided a 20-fold increase in the short circuit current under visible light illumination. This was further increased by a factor of approximately 1.5 by the photosensitization effect of CdTe, which has an optical absorption of up to 820 nm.

Photoconductivity of CdTe nanocrystal films in a simple multilayer device structure

The photoconductivity of CdTe nanocrystal films was investigated by employing a ZnO/CdTe/In multilayer device structure. CdTe was deposited on a ZnO electrode by a pulsed electron-beam technique at argon background gas pressures of 9, 13 and 17 mTorr. Using two photo-excitation sources (visible and near-infrared), the device with the CdTe deposited at 17 mTorr demonstrated the highest photocurrent to dark current ratio, suggesting the highest quantum efficiency among the three different devices. It also demonstrated the highest short circuit photocurrent and the fastest photocurrent decay. These results are attributed to the formation of more nanocrystals at 17 mTorr with enhanced optoelectronic properties.

Plasmon enhanced luminescence of Tb3+ doped Li2O-LaF3-Al2O3-SiO2 glass containing Ag nanoparticles

Tb3+ and Ag co-doped glass nano-composites are synthesized in a glass matrix Li2O-LaF3-Al2O3-SiO2 (LLAS) by a melt-quench technique. The nucleation and growth of Ag nanoparticles (NPs) were controlled by a thermal annealing process. A broad absorption band peaking at about 420 nm was observed due to surface plasmon resonance (SPR) of Ag NPs. Annealing of glass samples results in the growth of Ag NPs. Photoluminescence (PL) emission and excitation spectra were measured from glass samples with different Ag concentrations and different annealing times. Plasmon enhanced Tb3+ luminescence was observed at certain excitation wavelength regions. Luminescence quenching was observed for samples with high Ag concentration and longer annealing time. Our luminescence results suggest that there are two competitive effects, enhancement and quenching, acting on Tb3+ luminescence in the presence of Ag NPs. The enhancement of Tb3+ luminescence is mainly attributed to local field effects: the SPR of Ag NPs causes an intensified electromagnetic field around the NPs, resulting in enhanced optical transitions of Tb3+ ions in the vicinity. The quenching effect in the presence of Ag NPs suggests an energy transfer from Tb3+ ions to Ag NPs. The competition between the plasmonic enhancement and the quenching effect is discussed for samples with different Ag concentrations and annealing times.

Plasmon enhanced luminescence of Tb3+doped Li 2 O-LaF 3 -Al 2 O 3 -SiO 2 glass containing Ag nanoparticles

Tb3+ and Ag co-doped glass nano-composites are synthesized in a glass matrix Li2O-LaF3-Al2O3-SiO2 (LLAS) by a melt-quench technique. The nucleation and growth of Ag nanoparticles (NPs) were controlled by a thermal annealing process. A broad absorption band peaking at about 420 nm was observed due to surface plasmon resonance (SPR) of Ag NPs. Annealing of glass samples results in the growth of Ag NPs. Photoluminescence (PL) emission and excitation spectra were measured from glass samples with different Ag concentrations and different annealing times. Plasmon enhanced Tb3+ luminescence was observed at certain excitation wavelength regions. Luminescence quenching was observed for samples with high Ag concentration and longer annealing time. Our luminescence results suggest that there are two competitive effects, enhancement and quenching, acting on Tb3+ luminescence in the presence of Ag NPs. The enhancement of Tb3+ luminescence is mainly attributed to local field effects: the SPR of Ag NPs causes an intensified electromagnetic field around the NPs, resulting in enhanced optical transitions of Tb3+ ions in the vicinity. The quenching effect in the presence of Ag NPs suggests an energy transfer from Tb3+ ions to Ag NPs. The competition between the plasmonic enhancement and the quenching effect is discussed for samples with different Ag concentrations and annealing times.

Plasmon enhanced luminescence of Tb 3+ doped Li 2 O-LaF 3 -Al 2 O 3 -SiO 2 glass containing Ag nanoparticles

Tb3+ and Ag co-doped glass nano-composites are synthesized in a glass matrix Li2O-LaF3-Al2O3-SiO2 (LLAS) by a melt-quench technique. The nucleation and growth of Ag nanoparticles (NPs) were controlled by a thermal annealing process. A broad absorption band peaking at about 420 nm was observed due to surface plasmon resonance (SPR) of Ag NPs. Annealing of glass samples results in the growth of Ag NPs. Photoluminescence (PL) emission and excitation spectra were measured from glass samples with different Ag concentrations and different annealing times. Plasmon enhanced Tb3+ luminescence was observed at certain excitation wavelength regions. Luminescence quenching was observed for samples with high Ag concentration and longer annealing time. Our luminescence results suggest that there are two competitive effects, enhancement and quenching, acting on Tb3+ luminescence in the presence of Ag NPs. The enhancement of Tb3+ luminescence is mainly attributed to local field effects: the SPR of Ag NPs causes an intensified electromagnetic field around the NPs, resulting in enhanced optical transitions of Tb3+ ions in the vicinity. The quenching effect in the presence of Ag NPs suggests an energy transfer from Tb3+ ions to Ag NPs. The competition between the plasmonic enhancement and the quenching effect is discussed for samples with different Ag concentrations and annealing times.

Low Temperature Growth of ZnO Nanowires for Hybrid Chemical Sensors

Hybrid nanocomposites, such as ZnO nanowires embedded in conducting polymers, are very attractive for chemical sensing applications. Previous studies have shown that tuning ZnO nanowire concentration with respect to the polymer can be employed to tailor chemical sensitivity and selectivity. In this work, we investigate the effect of ZnO nanowire growth time on the electrical transport properties of sensors with and without the polymer matrix. Varying growth times may affect wire lengths, wire concentration, as well as wire interconnectivity. Using pure Zn as the source, ZnO nanowires are grown on a glass substrate by a low temperature thermal evaporation method. Poly(3-hexylthiophene) is employed as the polymeric matrix to form a hybrid structure. The response to ethanol vapor of sensors with different nanowire growth times is evaluated.Copyright