Semiconductor nanostructures exhibit remarkable optical and physical properties, including high absorption cross sections, narrow emission full-width at half-maximum (FWHM), highly tunable emission profiles, high photoluminescence quantum yields (PLQYs), and superior photochemical stability [1–5]. Due to quantum confinement effects, these properties become strongly size- and dimension-dependent when the physical dimensions of the nanostructure are smaller than the exciton Bohr radius of the bulk semiconductor. Incorporating alloyed compositions further enhances spectral tunability across a broader wavelength range; for instance, the emission of CdZnSe-based nanocrystal heterostructures (NCHs) can be tuned from 470 to 650 nm simply by varying the core's Cd/Zn ratio. Alternatively, the emission spectral range can be expanded using multiple confined nanocrystalline heterostructures. Dual quantum-confined NCHs featuring a wide-bandgap barrier have attracted significant interest due to their unique dual-band emission under ambient excitation. To exploit this, researchers have engineered several spherical quantum dot/barrier/quantum well (QD/barrier/QWell) NCHs—such as CdSe/ZnS/CdSe and PbS/CdS/CdSe core/inner-shell/outer-shell nanocrystals. In these architectures, both the QD core (CdSe or PbS) and the QWell outer shell (CdSe) exhibit distinct emission bands that can be independently modulated by adjusting the core diameter and outer-shell thickness, respectively. Furthermore, Mews et al. developed colloidal double-quantum wells based on CdS–HgS systems. Using a surface-replacement strategy to insert HgS layers between CdS barriers, the authors observed a significant red-shift in the absorption spectra of the complex nanocrystals, indicating strong electronic coupling between the two quantum wells.

However, spectral tuning in these QD–QWell dual-domain NCHs remains challenging due to inherent limitations in epitaxial growth. Depositing uniform QW layers onto the highly curved, multifaceted surfaces of QD cores often results in broad emission bandwidths and unpredictable intensities. This bottleneck can be overcome by synthesizing quantum wires (QWs) onto the QDs. For instance, Lim et al. reported QD/quantum rod (QR) NCHs that achieved dual-band emission by growing CdSe nanorods over CdSe/CdS QDs separated by a ZnS barrier layer. They utilized a photoetching technique to precisely tune the quantum confinement dimensions (such as QR width) simply by adjusting the excitation wavelength.

Here, we report a simple, conventional bottom-up colloidal growth strategy to synthesize sophisticated quantum dot–quantum wire (QD–QW) heterostructures with targeted optical properties. Anisotropic CdZnSe/ZnS core QDs were fabricated first, followed by the growth of multiple quantum wires on their surfaces. These NCHs exhibit precise, continuously tunable dual- and triple-band emissions. Through this multi-step colloidal route, we nanoengineered CdZnSe/ZnS/CdSe structures featuring a QD core, a ZnS shell, and CdSe nanorods to form dual- and triple-quantum-confined NCHs. We provide a detailed mechanism for the formation of these CdSe-based quantum wires. Crucially, the quantum wire thickness depends strictly on the reaction temperature and is independent of the synthesis duration. Core QDs of three distinct sizes (6.0 nm, 7.5 nm, and 8.5 nm) were synthesized by varying the reaction time and precursor concentration. Nanowires were then grown by exposing these core QDs to a subsequent round of CdSe precursors at various temperatures, yielding QD–QW NCHs with two distinct emission bands. To further enhance spectral tunability, the QD–QW structures were exposed to an additional round of CdSe precursors at a lower temperature. This step produced triple-quantum-confined QD–QW1–QW2 NCHs exhibiting three emission bands. To achieve white-light emission, blue-emitting core QDs were integrated with primary and secondary QWs. Finally, these sophisticated nanostructures were fabricated into white-light-emitting LEDs, demonstrating an external quantum efficiency (EQE) of 0.5%, which is highly comparable to the current literature benchmark of 0.66% for CdSe-based nanostructures.