title: Simultaneous type-I/type-II emission from CdSe/CdS/ZnSe nano-heterostructures.
abstract: Core/intermediate/shell (C/I/S) structures with Type-I emission are well-known and are gaining immense importance due to their superior luminescence properties. Here, we report a unique C/I/S structure composed of CdSe/CdS/ZnSe that exhibits both Type-I and Type-II phenomena. The structures have been well characterized using a combination of optical and structural techniques. The photoluminescence (PL) and photoluminescence excitation (PLE) data indicate the formation of a combined Type-I and Type-II structure in one material, results supported by simple theoretical calculations. Single particle fluorescence reveals colocalization of both the emissions. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirm the structure of these particles. The time-resolved fluorescence studies show the possibility of tuning the lifetime of these materials by changing the Type-I/Type-II thickness ratios. It is possible to form these two separate excitons in the same system separated by a CdS intermediate layer that acts both as a barrier and an active member of the Type-II system allowing the generation and recombination of two excitons, in violation of Kasha's rule.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
authors.forename: Udit
authors.initials: U
authors.lastname: Soni
authors.forename: Anuushka
authors.initials: A
authors.lastname: Pal
authors.forename: Sajan
authors.initials: S
authors.lastname: Singh
authors.forename: Mona
authors.initials: M
authors.lastname: Mittal
authors.forename: Sushma
authors.initials: S
authors.lastname: Yadav
authors.forename: Ravikrishnan
authors.initials: R
authors.lastname: Elangovan
authors.forename: Sameer
authors.initials: S
authors.lastname: Sapra