= Exciton thermalization versus recombination
A population of <excitons> can approach a thermal distribution only if redistribution and cooling occur before too many excitons disappear. A useful necessary scale comparison is $\tau_{\rm therm}\ll\tau_{\rm life}$, where the lifetime includes radiative and nonradiative <recombination> and the thermalization time describes the relevant energy redistribution.
The inequality is not sufficient to establish <exciton condensation>: density, disorder, pumping and the stability of the excitons also matter. A continuously pumped short-lived population can have a stationary distribution without satisfying equilibrium statistical mechanics. Spectral narrowing or a nonlinear emission threshold can therefore support several interpretations. Relating such observations to condensation requires a model of creation, cooling, interactions and losses, as emphasized in <exciton condensation evidence and competing optical signatures>.
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