Controlled Core/Crown Growth Enables Blue‐Emitting Colloidal Nanoplatelets with Efficient and Pure Photoluminescence

Abstract

Colloidal semiconductor CdSe nanoplatelets (NPLs) feature ultranarrow and anisotropic emissions. However, the optical performance of blue‐emitting NPLs is deteriorated by trap states, currently exhibiting tainted emissions and inferior photoluminescence quantum yields (PLQYs). Here, near trap‐free blue‐emitting NPLs are achieved by the controlled growth of the core/crown. Deep trap states in NPLs can be partially suppressed with the asymmetrical crown growth and are further suppressed with the growth of the small core and the alloyed symmetrical crown, yielding NPLs with pure blue emissions and near‐unity PLQYs. Exciton dynamic research based on these NPLs indicates that the trap emission stems from surface traps. Besides, light‐emitting diodes exhibiting ultranarrow emission centered around 461 nm with full‐width‐at‐half‐maximums down to 11 nm are fabricated using these NPLs.

Atomically flat semiconductor nanoplatelets for light-emitting applications

“…Therefore, triangular 3.5 ML CdSe NPLs with a symmetrical shape were obtained, facilitating the symmetrical growth of CdSeS crowns. 186 The obtained blue-emitting triangle-shaped 3.5 ML CdSe/CdSeS core/crown NPLs possessed a narrow emission with a FWHM of 10 nm and a near-unity PLQY. The combination of alloyed and asymmetrical crowns provided a possibility for NPLs with near-unity PLQY but without any broadening of emission, which enabled the high color purity blue and green LEDs.…”

“…This was because the interface defects were not completely suppressed by the asymmetrical growth of CdSeS crowns on the sidewalls of rectangle-shaped 3.5 ML CdSe NPLs due to the unfavorable growth of (110) facets induced by the adsorption of short-chain ligands. 186 As Cd(propionate) 2 was employed instead of propionic acid, the high ratio of Cd and Se precursors altered the growth directions from [100] to [110]. Therefore, triangular 3.5 ML CdSe NPLs with a symmetrical shape were obtained, facilitating the symmetrical growth of CdSeS crowns.…”

“…The combination of alloyed and asymmetrical crowns provided a possibility for NPLs with near-unity PLQY but without any broadening of emission, which enabled the high color purity blue and green LEDs. 185,186 The epitaxial growth of CdSe crowns on the sidewalls of CdS NPLs results in inverted type-I CdS/CdSe core/crown NPLs, and both CdS cores and CdSe crowns possess same thickness. 188 In CdSe/CdS core/crown NPLs, due to the strong exciton confinement in the CdSe NPL core, the emission energy is independent of the lateral size of CdS crowns.…”

“…The combination of alloyed and asymmetrical crowns provided a possibility for NPLs with near-unity PLQY but without any broadening of emission, which enabled the high color purity blue and green LEDs. 185,186…”

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

“…The lowest threshold reaches an ultralow value of 9.1 μJ/cm 2 when the cavity mode is located in the central wavelength of the biexciton emission. Our results show that CdSe/CdSeS core/alloyed-crown NPLs are excellent optical gain media in the green-color range due to their low ASE and lasing thresholds, in addition to their excellent emission tunability. , …”