R. Peña Sierra

Thermal ionisation of ground and multiply excited states in InAs quantum dots embedded into InGaAs/GaAs MQW

The photoluminescence (PL) spectra of highly uniform self-assembled InAs quantum dots (QDs) embedded in In 0.15 Ga 0.85 As multi-quantum-well (MQW) heterostructures have been investigated at variable temperatures. This paper presents the PL bands, connected with ground (GS) and multi-excited states (ES) in QDs. Not equidistant optical transitions have been revealed. Spectral peak shifts and PL intensity variations in the temperature range 12-220 K for all PL bands are analyzed. The activation energy of the temperature quenching processes for GS and 4 ES optical transitions in InAs QDs are measured. The mechanism of these processes and the positions of the energy levels in QDs are discussed as well.

Modification of optical properties at bioconjugation of core-shell CdSe/ZnS quantum dots

This paper presents the results of photoluminescence study of core-shell CdSe/ZnS quantum dots (QDs) with radiative interface states in nonconjugated and bioconjugated conditions. PL spectra of nonconjugated QDs are characterized by a superposition of PL bands related to exciton emission in CdSe cores (2.36 eV) and to electron-hole emission via interface states (2.00, 2.75 and 3.04 eV) at the CdSe/ZnS or ZnS/polymer interfaces. The CdSe/ZnS QDs with emission at 525 nm have been conjugated with bio-molecules – mouse ovarian cancer (OC 125) antibodies. It is revealed that PL spectrum of bioconjugated QDs has changed dramatically with essential decreasing of the hot electron-hole recombination flow via interface states. This effect is explained on the base of the model deals with re-charging of QD interface states at the bioconjugation with OC125 antibodies. The nature of interface states and their changes at the QD aging process have been discussed as well.

Power-quality model based on IGBT dynamic-conduction for non-polluting lighting applications

In this paper, a power-quality model based on dynamic-conduction of the modern switching power devices is presented. The power-quality analysis is needed due to the serious problems by the compact fluorescent lamps (CFL) technology, including generation of poor power-quality and the risks on the human health because the CFL contain mercury. The proposed model utilizes normalized symbolic functions of the current conduction functions defined by closed time intervals, which has been applied to a single-phase AC-DC converter. Also, the total harmonic distortion (THD) is evaluated to demonstrate the improvement of the power quality as a function of the normalized Fourier coefficients. The principle of operation of the single-phase AC-DC converter is presented and the results indicate that power quality would be enhanced using incandescent lamps with lower power consumption.

Multiple excited state modification in InAs/InGaAs quantum dot structures at high excitation power

Abstract This paper presents the investigation of photoluminescence (PL), connected with ground (GS) and four excited states (1–4-ES) in highly uniform self-assembled InAs quantum dots (QDs) embedded into the In 0.15 Ga 0.8 As layers, using variable pumping power (P) in the range 10–1000xa0W/cm 2 at the temperature 12xa0K. The peak positions of GS and ES emission bands depend on an excitation light power. The energy differences between GS and 1–4ES optical transitions are not equidistant and equal to 48.8, 46.5, 40.3 and 33.4xa0meV, respectively, at highest power level. It was shown that many-particle effects in such high populated QDs is essential and the exchange/correlation and direct Coulomb contributions do not vanish in the investigated strong confined QDs.

Multishell photoluminescence from InAs/InGaAs quantum dots

Photoluminescence spectra are investigated of InAs/InGaAs QD structures prepared be MBE on GaAs substrates in a range of pumping power density up to 0.6 kW/cm2. Multiple spectra band are observed corresponding to electron shells in atom-like dots. Identification of shells is proposed on the basis of spherical oscillator model. Energy diagram of dots is proposed taking into account identical temperature dependence of PL intensity in three lowest spectral bands.