Control of the photoluminescence lifetime of quantum dots by engineering their shell structure

Quantum dots (QDs) are semiconductor nanocrystals with outstanding photoluminescence (PL) characteristics: a PL quantum yield as high as 100%, a small PL emission bandwidth, and a high emission brightness. Due to these properties, QDs have a wide range of prospective applications in optoelectronics, quantum technologies, and biomedicine. The PL lifetime is one of the most important characteristics of QDs and a crucial parameter for their applicability in many specific areas of science and technology. Although this characteristic varies widely for QDs of different chemical compositions and structures, the most common type of QDs based on CdSe cores rarely has a lifetime longer than 30 ns. In this study, an effective method for increasing the QD PL lifetime is proposed. This method consists in the formation of a gradient shell on the surface of CdSe cores, which creates a potential well for excited charge carriers. This approach makes it possible to fabricate QDs with an average PL lifetime of about 100 ns, which is more than three times higher than this parameter for the best samples of such materials reported in the literature.