Bright Light Emission from Deep Energy States.

Deep energy states, a fundamental concept in semiconductor physics, play a pivotal role in determining the optical performance of semiconductor materials. They are generally regarded as undesirable defects, as they can serve as efficient centers for non-radiative recombination. Thus, the prevailing consensus is that deep energy states must be passivated and mitigated to enhance the optical properties of semiconductors. In this work, however, it is demonstrated that these " undesirable" deep energy states can be harnessed as " desirable" states to enable bright light emission. This is achieved by proposing a deep energy state regulation mechanism, termed "surface ionization annealing", which transforms the randomly and broadly distributed non-radiative deep energy levels into a narrower energy range. This transformation results in a high density of states and band-edge-like absorption originating from deep energy states in sulfur quantum dots. The regulation is realized through precise control of surface charge and surface dangling bonds. Simultaneously, surface ionization annealing eliminates non-radiative deep energy states, significantly enhancing the photoluminescence quantum yield (PLQY) of sulfur quantum dots to 15.6%. Consequently, the simultaneous realization of a high density of states and high PLQY enables bright light emission from deep energy states.