1 research outputs found
Size-Dependent Extinction Coefficients and Transition Energies of Near-Infrared β‑Ag<sub>2</sub>Se Colloidal Quantum Dots
Our investigations of silver selenide
colloidal quantum dots, emitting
in the biologically important near-infrared region, demonstrate the
size-dependence of their optical properties. Ag<sub>2</sub>Se nanocrystals
were prepared in the orthorhombic phase with their average radius
varying from 0.95 to 4.7 nm as observed by transmission electron microscopy.
The high purity of the samples, established by energy-dispersive X-ray
spectroscopy and X-ray diffraction, allowed for the accurate determination
of the Ag<sub>2</sub>Se content of colloidal suspensions by a thermogravimetric
method. The energy of the first observed transition is found to decrease
asymptotically with colloidal quantum dot size, tending toward a value
of 1.1 eV, a value significantly above the β-Ag<sub>2</sub>Se
bulk bandgap. Furthermore, the molar extinction coefficient of this
absorption is proportional to <i>r</i><sub>0</sub><sup>2.7±0.2</sup>, where <i>r</i><sub>0</sub> is the cQD radius. At higher
energies, the extinction coefficient eventually follows the classically
predicted cubic power law with <i>r</i><sub>0</sub>