Pushing the Emission Envelope for Full-Color Realization of Colloidal Semiconductor Core/Shell Nanoplatelets

Abstract

Colloidal semiconductor nanoplatelets (NPLs) have been known to exhibit favorable optical characteristics, such as a narrow emission bandwidth, giant oscillator strength, suppressed Auger recombination, and polarized emission, which can merit their use in light-emitting diodes and lasing devices. However, to date, NPLs have shown a relatively limited range of emission energy because of their thickness-dependent discrete band gap and restricted choice of chemical composition (mostly CdSe-based), impeding the realization of R, G, and B full-color display based on NPLs. CdSe-based core/shell NPLs can only cover the emission range from yellowish green (∼550 nm) to red (∼620 nm). In this study, we synthesize CdZnSe/ZnS core/shell NPLs with significantly enhanced spectral tunability over a broad spectral range (425–570 nm). Particularly, to overcome the difficulty in the synthesis of composition-controlled CdZnSe NPLs, we carried out a Cd-to-Zn direct cation exchange reaction on CdSe/ZnS core/shell NPLs using ZnI2 and an oleylamine (or trioctylphosphine oxide) ligand, which allows for the composition change in NPL emitting core while maintaining the original shape of NPLs. With the control of the reaction temperature and time as well as the ligands, the exchange reaction enables us to demonstrate an unprecedentedly wide emission range and spectral tunability of NPLs with the emission wavelength reaching 425 nm. Furthermore, as the core alloying proceeds, NPLs maintain excellent color purity and exhibit linearly polarized emission. Our light-emitting devices using the cation-exchanged CdZnSe/ZnS NPLs hinted at the possibility of using the NPLs in full-color display applications. Based on the elemental mapping analysis and experimental results, we proposed the temperature-dependent cation exchange reaction process in core/shell NPLs.

Low-Threshold Single-Mode Microlasers from Green CdSe/CdSeS Core/Alloyed-Crown Nanoplatelets

“…Based on this characteristic, combined with the fact that core/alloyed-crown NPLs can have different central wavelengths covering 500− 550 nm, 43 a wide range of single-mode lasing can be achieved covering the visible light range, as long as the wavelength of the cavity in the device is reasonably designed. It is possible to obtain even lower threshold lasers by improving the Q factor of the cavity arrays, e.g., modes based on bound states in the continuum reaching a Q factor of 2590, 28 and using core/shell NPLs in the blue-and green-color range recently reported by Yoon et al 53 ■ CONCLUSIONS…”

Scalable Ammonia Synthesis in Fermentors Using Quantum Dot-Azotobacter vinelandii Hybrids

“…A set of unique optical and photophysical characteristics, such as size-tunable bandgap of semiconductors, has been the impetus for the precise control of their conduction and valence band energy levels. This property facilitates applications in high-resolution displays and LED lighting with enhanced brightness [17][18][19]. Additionally, these properties open opportunities in catalysis and environmental applications, where their photoexcited electron-hole pair formation can catalyze chemical reactions [20][21][22][23][24][25][26][27].…”