Zero-Dimensional Lead-Free Halide with Indirect Optical Gap and Enhanced Photoluminescence by Sb Doping

Three
new lead-free organic–inorganic metal halides (OIMHs)
(C7H8N3)3InX6·H2O (X = Cl, Br) and (C7H8N3)2SbBr5 were synthesized. First-principles
calculations indicate that the highest occupied molecular orbitals
(HOMOs) of the two In-based OIMHs are constituted of π orbitals
from [C7H8N3]+ spacers.
(C7H8N3)3InX6·H2O (X = Cl, Br) shows an indirect optical gap,
which may result from this organic-contributed band edge. Despite
the indirect-gap nature with extra phonon process during absorption,
the photoluminescence of (C7H8N3)3InBr6·H2O can still be significantly
enhanced through Sb doping, with the internal photoluminescence quantum
yields (PLQY) increased 10-fold from 5% to 52%. A white light-emitting
diode (WLED) was fabricated based on (C7H8N3)3InBr6·H2O:Sb3+, exhibiting a high color-rendering index of 90. Our work provides
new systems to deeply understand the principles for organic spacer
choice to obtain the 0D metal OIMHs with specific band structure and
also the significant enhancement of luminescence performance by chemical
doping.