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.