  One-dimensional (1D) van der Waals materials have emerged as an intriguing
playground to explore novel electronic and optical effects. We report on
inorganic one-dimensional SbPS4 nanotubes bundles obtained via mechanical
exfoliation from bulk crystals. The ability to mechanically exfoliate SbPS4
nanobundles offers the possibility of applying modern 2D material fabrication
techniques to create mixed-dimensional van der Waals heterostructures. We find
that SbPS4 can readily be exfoliated to yield long (> 10 {\mu}m) nanobundles
with thicknesses that range from of 1.3 - 200 nm. We investigated the optical
response of semiconducting SbPS4 nanobundles and discovered that upon
excitation with blue light, they emit bright and ultra-broadband red light with
a quantum yield similar to that of hBN-encapsulated MoSe2. We discovered that
the ultra-broadband red light emission is a result of a large ~1 eV exciton
binding energy and a ~200 meV exciton self-trapping energy, unprecedented in
previous material studies. Due to the bright and ultra-broadband light
emission, we believe that this class of inorganic 1D van der Waals
semiconductors has numerous potential applications including on-chip tunable
nanolasers, and applications that require ultra-violet to visible light
conversion such as lighting and sensing. Overall, our findings open avenues for
harnessing the unique characteristics of these nanomaterials, advancing both
fundamental research and practical optoelectronic applications.
