Shape-Selective Optical Transformations of CdSe Nanoplatelets Driven by Halide Ion Ligand Exchange

Treatment of CdSe nanoplatelets with halide salts induces a bathochromic shift in the absorption resonances that does not occur in quasi-spherical quantum dots of the same composition. The optical shifts are not strongly sensitive to the cation moiety, which may be organic or inorganic. The magnitude of the energy shift is largest for thinner nanoplatelets, with bathochromic shifts as large as 240 meV observed for 3 monolayer nanoplatelets. This effect is driven by a tetragonal distortion of the zinc blende lattice in response to ligand exchange. The expansion of the lattice in the shortest nanoplatelet axis results in the observed red-shifts due primarily to relaxation of quantum confinement, with secondary contributions from strain.