  Pulse-shape discrimination (PSD) is usually achieved using the different fast
and slow decay components of inorganic scintillators, such as BaF2, CsI:Tl,
etc. However, LaBr3:Ce is considered to not possess different components at
room temperature, but has been proved to have the capability of discriminating
{\gamma} and {\alpha} events using fast digitizers. In this paper,
ionization-density-dependent transport and rate equations are used to
quantitatively model the competing processes in a particle track. With one
parameter set, the model reproduces the nonproportionality response of
electrons or {\alpha} particles, and explains the measured {\alpha} and
{\gamma} pulse-shape difference well. In particular, the nonlinear quenching of
excited dopant ions, Ce3+, is confirmed herein to mainly contribute observable
ionization {\alpha} and {\gamma} pulse-shape differences. Further study of the
luminescence quenching can also help to better understand the fundamental
physics of nonlinear quenching and thus improve the crystal engineering.
Moreover, based on the mechanism of dopant quenching, the
ionization-density-dependent pulse-shape differences in other fast
single-decay-component inorganic scintillators, such as lutetium yttrium
oxyorthosilicate, Lu2(1-x)Y2xSiO5:Ce (LYSO) and CeBr3, are also predicted and
verified with experiments.
