Nimai Mishra

Dual Wavelength Electroluminescence from CdSe/CdS Tetrapods

We fabricated a single active layer quantum dot light-emitting diode device based on colloidal CdSe (core)/CdS (arm) tetrapod nanostructures capable of simultaneously producing room temperature electroluminesence (EL) peaks at two spectrally distinct wavelengths, namely, at ∼500 and ∼660 nm. This remarkable dual EL was found to originate from the CdS arms and CdSe core of the tetrapod architecture, which implies that the radiative recombination of injected charge carriers can independently take place at spatially distinct regions of the tetrapod. In contrast, control experiments employing CdSe-core-seeded CdS nanorods showed near-exclusive EL from the CdSe core. Time-resolved spectroscopy measurements on tetrapods revealed the presence of hole traps, which facilitated the localization and subsequent radiative recombination of excitons in the CdS arm regions, whereas excitonic recombination in nanorods took place predominantly within the vicinity of the CdSe core. These observations collectively highlight the role of morphology in the achievement of light emission from the different material components in heterostructured semiconductor nanoparticles, thus showing a way in developing a class of materials which are capable of exhibiting multiwavelength electroluminescence.

Enhanced tunability of the multiphoton absorption cross-section in seeded CdSe/CdS nanorod heterostructures

We present a method to separately tune the multiphoton absorption (MPA) and multiphoton excited photoluminescence using semiconductor core/enlarged-shell quantum dots (QDs), where the enlarged shell greatly enhances the MPA cross-sections while varying the core size facilitates emission wavelength selectivity. Following two-photon absorption (2PA) primarily in the shell and ultrafast charge-carrier localization to the core, luminescence occurs. We exemplify the validity of this method with CdSe/CdS nanorod heterostructures and find that the 2PA cross-section is enlarged to ∼1.4×106 GM for 180 nm nanorods (with 800 nm, 150 fs laser pulse excitation) which is two to four orders larger than that of CdSe QDs.

Low Threshold, Amplified Spontaneous Emission from Core‐Seeded Semiconductor Nanotetrapods Incorporated into a Sol–Gel Matrix

Wet-chemically synthesized colloidal semiconductor nanocrystals (NCs) are desirable as optical gain media due to their sizedependent emission wavelengths, ease of fabrication and fl exible surface chemistry which facilitates incorporation into an optical feedback device of various confi gurations. [ 1–3 ] Early attempts to achieve stimulated emission via close-packed fi lms of NCs required low temperature and high pump fl uences since such fi lms generally suffer from low optical quality, poor heat dissipation, and consequently short operational device lifetimes. [ 4 , 5 ]

Engineering fluorescence in Au-tipped, CdSe-seeded CdS nanoheterostructures

Signifi cant advances in the wet chemical synthesis of colloidal semiconductor nanoparticles have afforded exquisite control over their size, shape, and composition, facilitating the development of multiple components within the same nanostructure and potentially multifarious functionalities. Metaltipped, seeded core–shell semiconductor nanorods exemplify such multicomponent heterostructures, where the metal tips can serve as an electrical contact [ 1–4 ] or provide an anchor point for self-assembly, [ 5 ] while the core–shell semiconductor can be engineered to exhibit unique optical properties. [ 6 , 7 ]

Metal–Semiconductor Hybrid Nano-Heterostructures for Photocatalysis Application

This chapter will address the development of colloidal synthesis of hybrid metal– semiconductor nanocrystals and their application in the field of photocatalysis. Despite the plethora of examples of different-shaped metal–semiconductor nanostructures that have been reported, metal-tipped semiconductor nanorods are perhaps the most intensively studied, and their use as a photocatalyst will be the focus of the chapter. First, we will discuss different wet-chemical synthesis techniques to control the synthesis of these metal–semiconductor hybrid structures. Afterward, we will discuss their unique physicochemical properties that are a combination of semiconductor and metal properties. Finally, we will showcase several examples from the literature demonstrating the possible application of these unique hybrid structures in photoca‐ talysis.