Composition-Tunable Optical Properties of Colloidal IV-VI Quantum Dots, Composed of Core/Shell Heterostructures with Alloy Components

Colloidal quantum dots (CQDs) attract worldwide scientific and technological attention due to the ability to engineer their optical properties by the variation of their size However;several,important applications, such as biological tagging and photovoltaic cells, impose a limit on their size yet demand tunability and thermal stability of the optical band edge,This work introduces a new class of heterostructures, composed of PbSe or PbSeyS1-y cores, coated by PbS or PbSexS1-x shells, with different core-radius/shell width division, with a radial gradient composition (with 0 < y < 1, 0 < x < 1), which offer a control of the band edge properties by varying the CQDs' composition Continuous wave and transient photoluminescence measurements over a wide temperature range (14-300 K) revealed a distinct behavior of the heterostructures with respect to that of pure PbSe cores (i) increase of the emission quantum yield; (Hired shift of the absorption edge but a decrease of the emission Stokes shift, (iii) alleviation of a dark exciton recombination; viz :a reduction of an exchange Interaction, (iv) tuning of the radiative lifetime with shell width and composition, (v) reduction of the band edge temperature coefficient dE/dT, viz, Induction of thermal stability. The k p envelope function,calculation, considerig abrupt or smooth alloying continuation of the potential at the core-shell interface revealed a delocalization of the hole entire volume of the CQDs; as a partial marked tunability, nonetheless preserving a desired size