Tuning radiative lifetimes in semiconductor quantum dots

Abstract

Photonic devices stand to benefit from the development of chromophores with tunable, precisely controlled spontaneous emission lifetimes. Here, we demonstrate a method to continuously tune the radiative emission lifetimes of a class of chromophores by varying the density of electronic states involved in the emission process. In particular, we examined the peculiar composition-dependent electronic structure of copper doped CdZnSe quantum dots. It is shown that the nature and density of electronic states involved with the emission process is a function of copper inclusion level, providing a very direct handle for controlling the spontaneous lifetimes. The spontaneous emission lifetimes are estimated by examining the ratios of emission lifetimes to absolute quantum yields and also measured directly by ultrafast luminescence upconversion experiments. We find excellent agreement between these classes of experiments. This scheme enables us to tune spontaneous emission lifetimes by three orders of magnitude from ∼15 ns to over ∼7 µs, which is unprecedented in existing lumophores.

Optical Properties and Electronic Structure of Copper Zinc Sulfide Nanocrystals

“…These effects that are absent in dilute systems become extremely significant in concentrated alloys. We note that this broadening is supplementary to the already large Cu emission line widths that are observed in the case of dilute Cu doped systems. ,,− The HMA picture thus accounts for both a red-shifting of the absorption edge and a broadening of the emission spectrum . Within the HMA picture, the excitation of a smaller subset of the broadened Cu to host transitions by low-energy photons leads to the commensurate narrowing of the emission.…”

“…25,26,37−39 The HMA picture thus accounts for both a red-shifting of the absorption edge and a broadening of the emission spectrum. 27 Within the HMA picture, the excitation of a smaller subset of the broadened Cu to host transitions by low-energy photons leads to the commensurate narrowing of the emission. These aspects are highlighted in Figure 3d.…”

“…In addition, Cu has also been shown to alloy into II–VI hosts leading to the emergence of an unusual class of highly mismatched alloys . Previous reports have described the alloying of Cu into CdZnSe and ZnSe hosts. , In the latter case, Cu has been shown to introduce d levels into the host bandgap, giving rise to an absorption tail as well as composition tuned spontaneous emission rates . Here we investigate the optical and electronic structure effects that result from Cu incorporation into a wide gap sulfide host, viz.…”

“…25,26 In the latter case, Cu has been shown to introduce d levels into the host bandgap, giving rise to an absorption tail as well as composition tuned spontaneous emission rates. 27 Here we investigate the optical and electronic structure effects that result from Cu incorporation into a wide gap sulfide host, viz. ZnS.…”

Theoretical Model for Luminescence Broadening and Anomalous Carrier Dynamics in Chalcopyrite Quantum Dots

“…While the vibronic coupling model provides an accurate estimate of a number of steady state and dynamic spectroscopic details of chalcopyrite QDs, it is evident that it is still incapable of addressing the extremely large emission line widths as well as a residual 430 meV Stokes shift that is encountered in early time emission spectra determined through luminescence upconversion. The current understanding of spectroscopic properties of these materials relies heavily on defects to explain Stokes shift although explanations based on fine structure have also been proposed. − Although this picture relies on an s–p character of the CB and VB respectively, other studies suggest a d-like valence band edge. , Other available theoretical and experimental , results that suggest coexistence of both differences and similarities between I–III–VI 2 and Cu doped II–VI materials.…”