Onset of exciton-exciton annihilation in single layer black phosphorus
  The exciton dynamics in monolayer black phosphorus is investigated over a very wide range of photoexcited exciton densities using time resolved photoluminescence. At low excitation densities, the exciton dynamics is successfully described in terms of a double exponential decay. With increasing exciton population, a fast, non-exponential component develops as exciton-exciton annihilation takes over as the dominant recombination mechanism under high excitation conditions. Our results identify an upper limit for the injection density, after which exciton-exciton annihilation reduces the quantum yield, which will significantly impact the performance of light emitting devices based on single layer black phosphorus. 
A. Surrente, A. A. Mitioglu, K. Galkowski, L. Klopotowski, W. Tabis,   B. Vignolle, D. K. Maude and P. Plochocka
cond-mat.mes-hall