We observe that the wavefunction overlap of the carriers in type-IIb quantum dots can be controlled by magnetic doping and strongly depends on the excitation power density. We study epitaxially grown ZnTe/ZnSe and magnetically doped (Zn,Mn)Te/ZnSe quantum dots that show a fast and slow recombination channel at two different energies. The emission shift of the slow recombination is independent of excitation power density (Pex), whereas the fast recombination channel exhibits a larger emission shift with increasing Pex. This blue shift saturates for high Pex, however at a lower Pex and smaller maximum shift in the magnetic system compared to the nonmagnetic system. The emission wavelength immediately after pulsed excitation typically changes as a function of charge carrier density due to the spatially indirect nature of type-IIb quantum dots. As carriers increase, the confinement potential of the system is altered due to a Coulomb interaction. The magnetic system exhibits a limited change in the wavefunction overlap of the carriers for high excitation power densities which we attribute to magnetic interactions to the hole wavefunction inside the dot. This would allow for an external manipulation of the magnetic polaron binding energy through varying the excitation power density Pex in quantum dots.
Fluorescent nanomaterials such as metal nanoclusters (NCs) have become one of the most essential nanomaterial and attracted abundant attention in research due to their excellent photophysical properties and wide range of applications. Furthermore, metal nanoclusters have been predominantly investigated owing to its excellent optical properties, simple synthetic routes,low toxicity and excellent photostability. However, limited advancements and progress have been executed in fabricating hydrophilic and highly luminescent metal NCs. Copper is an eco-friendly, low-cost metal which is progressively advancing into focus for metal NCs research. In comparison to the extensively studied gold nanoclusters (Au NCs) and silver nanoclusters (Ag NCs), systematic and analytical applications of the copper nanoclusters (Cu NCs) are relatively limited and still at an early stage. In this review, we fixate on contemporary advances in the analytical applications of Cu NCs based on their behavior and properties of light. This work specifically addresses optical properties and some emerging applications of Cu NCs. The study seeks to unravel some unique photophysical properties of Cu NCs in its solid state, namely concentration/aggregation induced emission enhancement, thermally activated delayed fluorescence (TADF), by which both singlet and triplet excitons can be harvested. Furthermore, the as-synthesized Cu NCs used in this study was remarkably excellent, garnering ~20% quantum yield in colloidal and solid-state form, respectively. CuNC/PVA nano-composites can exhibit unique solidstate- induced dual-mode emissions of thermally activated delayed fluorescence (TADF) and phosphorescence at ambient environment. The outstanding performance of Cu NCs in solid-state makes it an excellent biocompatible nanoemitters light-emitting devices.
B. Barman, Y. Tsai, T. Scrace, J. Murphy, A. Cartwright, J. Pientka, I. Zutic, B. McCombe, A. Petrou, I. Sellers, R. Oszwaldowski, A. Petukhov, W. C. Fan, W. C. Chou, C. S. Yang
We used time resolved photoluminescence (TRPL) spectroscopy to compare the properties of magnetic polarons in
two related, spatially indirect, II-VI epitaxially grown quantum dot systems. In sample A (ZnMnTe/ZnSe), the photoexcited
holes are confined in the magnetic ZnMnTe quantum dots (QDs), while the electrons remain in the surrounding
non-magnetic ZnSe matrix. In sample B (ZnTe/ZnMnSe) on the other hand, the holes are confined in the non-magnetic
ZnTe QDs and the electrons move in the magnetic ZnMnSe matrix. The magnetic polaron formation energies, EMP , in
these samples were measured from the temporal red-shift of the excitonic emission peak. The magnetic polarons in the
two samples exhibit distinct characteristics. In sample A, the magnetic polaron is strongly bound with EMP=35 meV.
Furthermore, EMP has unconventionally weak dependence of on both temperature T and magnetic field Bappl . In
contrast, magnetic polarons in sample B show conventional characteristics with EMP decreasing with increasing
temperature and increasing external magnetic field. We attribute the difference in magnetic polaron properties between
the two types of QDs to the difference in the location of the Mn ions in the respective structures.
KEYWORDS: Oxides, Carrier dynamics, Temperature metrology, Spectroscopy, Luminescence, Solar energy, Time resolved spectroscopy, Excitons, Semiconductors, Chemical species
This study explores comprehensively the carrier dynamics in ZnSeO and ZnTeO using photoluminescence (PL) and
time-resolved PL spectroscopy. As the O concentration increases, the PL emissions shift toward lower energies.
Additionally, the PL lifetime increases with increasing O contents and the decay curves exhibit complex behavior. In the
case of ZnSeO, the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons
with the increase in temperature. The incorporation of O in ZnTe generates a wide distribution of electron localization
below the energy of the E- conduction subband, and these cause broad PL emission and serve as another intermediate band. Electrons in both the E+and the E-conduction subbands favor rapid relaxation to low energy states. Moreover, temperature-independent long carrier lifetimes (> 130.0 ns) that are induced by localized electrons increase with O concentration.
The dynamics of Förster resonance energy transfer (FRET) in mixed-size water-soluble CdTe quantum dots (QDs)
are studied by using photoluminescence (PL) and time-resolved PL spectroscopy. When donor concentration is increased,
an enhancement of both the FRET and quantum efficiency in the mixed-size CdTe QDs films can be observed.
Increasing donor concentration significantly quenches the emission intensity and lifetime in donor QDs and enhances
that in acceptor QDs. However, as D/A ratios exceed 6, the emission intensity and the lifetime of acceptor QDs start to
decline, reflecting a decreasing in both quantum and FRET efficiency due to a markedly declining availability of
acceptor QDs.
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