Full-Spectrum White-Light Emission from Triple Self-Trapped Excitons in Hybrid Mixed-Metal Halides

Low-dimensional metal halides with
broadband emissions are expected
to serve as downconversion luminescent materials for solid-state lighting
(SSL). However, efficiently generating full-spectrum white-light emission
with a high color-rendering index (CRI) in single-phase emitters remains
a challenge. Here, we report a novel zero-dimensional (0D) hybrid
mixed-metal halide (TPA)2CuAgI4 (TPA = tetrapropylammonium),
in which individual [CuAgI4]2– dimers
are completely isolated and surrounded by the organic cations TPA+. Cu+ and Ag+ share the same crystallographic
site in [CuAgI4]2– dimers with the same
statistical probability. Upon photoexcitation, single crystals exhibit
a full-spectrum white-light emission with a full width at half-maximum
(fwhm) of up to 314 nm and a high quantum efficiency of 46.8%. Detailed
photophysical studies and theoretical calculations reveal that the
ultra-broadband emission of (TPA)2CuAgI4 originates
from the radiative recombination of red-, green-, and blue-emitting
self-trapped excitons in [CuAgI4]2– dimers.
In addition, (TPA)2CuAgI4 nanocrystals were
successfully synthesized and exhibited optical properties similar
to those of single-crystal counterparts. Finally, a prototype ultraviolet
(UV)-pumped white-light-emitting diode (WLED) and a composite thin
film employing this new white-light emitter produces a well-distributed
full-spectrum white light with a high CRI of 91.4 and a warm correlated
color temperature (CCT) of 4135 K, indicating the potential application
of this white-light emitter in SSL. These results provide a new perspective
for designing superior single-phase white-light emitters.