Highly Luminescent Zero-Dimensional Organic Copper Halide with Low-Loss Optical Waveguides and Highly Polarized Emission

Zero-dimensional
(0D) copper-based metal halides have exhibited
great potential as luminescent materials with structural tunability
and impressive emission properties. Luminescence from highly ordered
self-assembly of copper halides is typically characterized by high
photoluminescence quantum efficiencies (PLQEs) and large Stokes shifts,
which are the most attractive features for active optical waveguides.
Here, we report a novel highly luminescent organic copper halide,
(PTMA)3Cu3I6 (PTMA: phenyltrimethylammonium),
in which individual face- and edge-sharing [Cu3I6]3– clusters are surrounded by PTMA+ organic molecules, forming a highly ordered 0D crystal structure
at the molecular level. Upon photoexcitation, (PTMA)3Cu3I6 single crystals exhibit a broadband yellow emission
with a high PLQE of up to 80.3%. Theoretical calculations revealed
that the photogenerated electron–hole pairs in (PTMA)3Cu3I6 are spatially separated from each other,
i.e., electrons are preferred to be localized in PTMA+ organic
molecules, while holes are highly localized in the inorganic [Cu3I6]3– clusters; thus, the emission
arises from the radiative recombination of ligand-to-metal charge
transfer (LMCT). In addition, colloidal nanocrystals of (PTMA)3Cu3I6 were successfully prepared, which
show similar luminescence properties with their single crystals. The
high PLQE, negligible self-absorption as well as the highly ordered
self-assembly of metal halide clusters make (PTMA)3Cu3I6 microplates promising materials for low-loss
optical waveguides, exhibiting an optical loss coefficient of 0.0157
dB μm–1 and highly linear polarized luminescence
with a polarization anisotropy of 1.78.