  The development of X-ray scintillators with ultrahigh light yields and
ultrafast response times is a long sought-after goal. In this work, we
theoretically predict and experimentally demonstrate a fundamental mechanism
that pushes the frontiers of ultrafast X-ray scintillator performance: the use
of nanoscale-confined surface plasmon polariton modes to tailor the
scintillator response time via the Purcell effect. By incorporating
nanoplasmonic materials in scintillator devices, this work predicts over
10-fold enhancement in decay rate and 38% reduction in time resolution even
with only a simple planar design. We experimentally demonstrate the
nanoplasmonic Purcell effect using perovskite scintillators, enhancing the
light yield by over 120% to 88 $\pm$ 11 ph/keV, and the decay rate by over 60%
to 2.0 $\pm$ 0.2 ns for the average decay time, and 0.7 $\pm$ 0.1 ns for the
ultrafast decay component, in good agreement with the predictions of our
theoretical framework. We perform proof-of-concept X-ray imaging experiments
using nanoplasmonic scintillators, demonstrating 182% enhancement in the
modulation transfer function at 4 line pairs per millimeter spatial frequency.
This work highlights the enormous potential of nanoplasmonics in optimizing
ultrafast scintillator devices for applications including time-of-flight X-ray
imaging and photon-counting computed tomography.
