  Colloidal core/shell nanocrystals are key materials for optoelectronics,
enabling control over essential properties via precise engineering of the
shape, thickness, and crystal lattice structure of their shell. Here, we apply
the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds
and obtain bone-shaped heterostructures with a highly anisotropic shell.
Surprisingly, the nanoplatelets withstand the high growth temperature of 350
{\deg}C and we obtain structures with a CdSe nanoplatelet core that is
overcoated by a shell of cubic CdS, on top of which tetrahedral CdS structures
with hexagonal lattice are formed. These complex core/shell nanocrystals show a
bandedge emission around 657 nm with a photoluminescence quantum yield of ca.
42 % in solution, which is also retained in thin films. Interestingly, the
nanocrystals manifest simultaneous red and green emission, and the relatively
long wavelength of the green emission indicates charge recombination at the
cubic/hexagonal interface of the CdS shell. The nanocrystal films show
amplified spontaneous emission, random lasing, and distributed feedback lasing
when the material is deposited on suitable gratings. Our work stimulates the
design and fabrication of more exotic core/shell heterostructures where charge
carrier delocalization, dipole moment, and other optical and electrical
properties can be engineered.
