Nanooptics and photonics

Time-Resolved Photoluminescence of CdSe/CdS/CdZnS Quantum Dots
Beloussov I.V., Pavlenko V.I., Dobynde I.I.
Institute of Applied Physics, 5 Academy str., Kishinev, 2028, Republic of Moldova.
E-mail: pavlenko@phys.asm.md

We used CdSe/CdS/CdZnS colloidal quantum dots (QDs) prepared by a standard chemical synthesis method dispersed in low concentration into toluen in a 1 mm length quartz cuvette. A sample with the photoluminescense (PL) peak at 628 nm was studied. The diameter of the CdSe nucleus of QD amounts to 5.4 nm with the size dispersion of 8%. The thickness of the CdS/CdZnS shell was 2.6 nm. The PL in QDs was excited by a single 38 ps pulse of the second harmonic (539 nm) of a mode-locked YAlO3: Nd3+ laser at room temperature. The spectral decomposition of the PL signal collected from the front face of the cuvette was performed using a polychromator. The PL kinetics was recorded by a streak camera. The PL spectrum is located along the streak camera entrance slit. The image of time-resolved PL spectrum of QDs obtained on the streak camera screen was registered by a digital camera. The time-resoved kinetics of PL is presented in Fig. 1.

Fig. 1. The observed dependence of the PL intensity on the time is represented by circles. A thin solid line corresponds to the solution of the rate equations. Thick lines describe PL kinetics from excitons (solid) and biexcitons (dotted) separately. The exciting pulse of duration 38 ps is centered at time 154 ps. Insert: Transient PL spectrum recorded at t=208 ps, integrated in 50 ps gate (circles) and its fitting curve (thin solid line). PL spectra for excitons (thick solid line) and biexcitons (thick dashed line). Time-integrated PL spectrum is shown as shaded area.