Infrared Emitting PbS Nanocrystal Solids through Matrix Encapsulation

Colloidal semiconductor nanocrystals (NCs) are emerging as promising infrared-emitting materials, which exhibit spectrally tunable fluorescence, and offer the ease of thin-film solution processing. Presently, an important challenge facing the development of nanocrystal infrared emitters concerns the fact that both the emission quantum yield and the stability of colloidal nanoparticles become compromised when nanoparticle solutions are processed into solids. Here, we address this issue by developing an assembly technique that encapsulates infrared-emitting PbS NCs into crystalline CdS matrices, designed to preserve NC emission characteristics upon film processing. An important feature of the reported approach is the heteroepitaxial passivation of nanocrystal surfaces with a CdS semiconductor, which shields nanoparticles from the external environment leading to a superior thermal and chemical stability. Here, the morphology of these matrices was designed to suppress the nonradiative carrier decay, whereby increasing the exciton lifetime up to 1 μs, and boosting the emission quantum yield to an unprecedented 3.7% for inorganically encapsulated PbS NC solids.