Magnetic field insensitive photoluminescence decay of ZnSe/CdS core/shell type-II colloidal quantum dots

We have synthesized ZnSe/CdS core/shell type-II colloidal quantum dots, where an electron and a hole are separated in the CdS shell and the ZnSe core, respectively. Our theoretical model has revealed that absorbance spectrum of bare ZnSe quantum dots in 2 nm radius becomes broadened with a large redshift (∼1.15 eV) when the electron in ZnSe core is separated by 3.2nm CdS shell. Also, we found that our type-II QDs are insensitive to an external magnetic field up to 5 T in terms of central emission energy, degree of polarization, and photoluminescence decay time. This can be attributed to the electron-hole charge separation in a type-II structure, whereby the suppressed exchange interaction gives rise to a magnetic insensitivity with a small energy difference between the bright and dark exciton states.