  Innovations in imaging technology involves finding strategies and materials
suitable for detection applications over the entire infrared range. Herein, we
propose a new design concept based on the unique feature of an excitonic
insulator, namely, negative exciton transition energy ($E_t$). We demonstrate
this concept using first-principles $GW$-BSE calculations on one-dimensional
organometallic wire (CrBz)$_\infty$. The pristine (CrBz)$_\infty$ exhibits an
excitonic instability due to a negative $E_t$ for the lowest exciton.
Substitutional doping can continuously tune the $E_t$ from $\sim$0 to $\sim$0.6
eV, which shows the ability of photon detection from terahertz to
near-infrared. This type of detectors have advantages of outstanding wavelength
selectivity, reduced thermal disturbance and elevated working temperature. Our
work not only adds another member in the family of rare one-dimensional
excitonic insulators, but also opens a new avenue for the development of
high-performance infrared photodetectors in the future.
