  Multiply twinned particles, MTPs, are fascinating crystallographic entities
with a number of controllable properties originating from their symmetry and
cyclic structure. In the focus of our studies are diamond MTPs hosting
optically active defects, objects demonstrating a high application potential
for emerging optoelectronic and quantum devices. In this work, we discuss the
growth mechanisms along with the microstructural and optical properties of the
MTPs aggregating high-density of silicon-vacancy complexes on the specific
crystal irregularities. It is demonstrated that the silicon impurities incite a
rapid growth of MTPs via intensive formation of penetration twins on 100 facets
of regular octahedral grains. We also show that the zero-phonon-line emission
from the Si color centers embedded in the twin boundaries dominates in photo-
and electroluminescence spectra of the MTP-based light-emitting devices
defining their steady-state optical properties.
