Luminescent CdSe Superstructures: A Nanocluster Superlattice and a Nanoporous Crystal

Superstructures,
combining nanoscopic constituents into micrometer-size
assemblies, have a great potential for utilization of the size-dependent
quantum-confinement properties in multifunctional electronic and optoelectronic
devices. Two diverse superstructures of nanoscopic CdSe were prepared
using solvothermal conversion of the same cadmium selenophenolate
precursor (Me4N)2[Cd­(SePh)4]: the
first is a superlattice of monodisperse [Cd54Se32(SePh)48(dmf)4]4– nanoclusters; the second is a unique porous CdSe crystal. Nanoclusters
were crystallized as cubic crystals (≤0.5 mm in size) after
solvothermal treatment at 200 °C in DMF. UV–vis absorption
and PLE spectra of the reported nanoclusters are consistent with previously
established trends for the known families of tetrahedral CdSe frameworks.
In contrast to these, results of PL spectra are rather unexpected,
as distinct room temperature emission is observed both in solution
and in the solid state. The porous CdSe crystals were isolated as
red hexagonal prisms (≤70 μm in size) via solvothermal
treatment under similar conditions but with the addition of an alkylammonium
salt. The presence of a three-dimensional CdSe network having a coherent
crystalline structure inside hexagonal prisms was concluded based
on powder X-ray diffraction, selected area electron diffraction and
electron microscopy imaging. Self-assembly via oriented attachment
of crystalline nanoparticles is discussed as the most probable mechanism
of formation.