Schulich Faculty of Chemistry, Russell Berrie Nanotechnology Institute, Solid State Institute, Technion, Haifa 32000, Israel.
ACS Nano. 2010 Nov 23;4(11):6547-56. doi: 10.1021/nn101760t. Epub 2010 Oct 14.
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 PbSe(y)S(1-y) cores, coated by PbS or PbSe(x)S(1-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 (1.4-300 K) revealed a distinct behavior of the heterostructures with respect to that of pure PbSe cores: (i) increase of the emission quantum yield; (ii) red-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, considering abrupt or smooth alloying continuation of the potential at the core-shell interface, revealed a delocalization of the hole wave function over the entire volume of the CQDs, as a partial explanation for the marked tunability, nonetheless preserving a desired size.
胶体量子点 (CQDs) 由于能够通过改变其尺寸来调整其光学性质，因此引起了全球科学界和技术界的关注。然而，一些重要的应用，如生物标记和光伏电池，对其尺寸有限制，但要求光学带边的可调谐性和热稳定性。本工作介绍了一类新的异质结构，由 PbSe 或 PbSe(y)S(1-y) 核组成，由 PbS 或 PbSe(x)S(1-x) 壳包裹，具有不同的核半径/壳宽度比，具有径向梯度组成（0 < y < 1，0 < x < 1），通过改变 CQDs 的组成来控制带边性质。在较宽的温度范围内（1.4-300 K）进行连续波和瞬态光致发光测量，发现异质结构的行为明显不同于纯 PbSe 核：(i) 发射量子产率增加；(ii) 吸收边缘红移但发射斯托克斯位移减小；(iii) 暗激子复合缓解，即交换相互作用减小；(iv) 辐射寿命随壳宽和组成可调谐；(v) 带边温度系数 dE/dT 减小，即诱导热稳定性。考虑到核壳界面处势的突然或平滑的合金连续性的 k·p 包络函数计算，揭示了空穴波函数在整个 CQDs 体积上的离域，这是明显可调谐性的部分解释，尽管保留了所需的尺寸。
