Fig. 3: Mechanism of ultralong intrinsic phosphorescence.

a PL spectra of AlN SC under X-ray and 266 nm laser excitation, respectively. b The DOS of AlN with potential defects, including VN, VAl, ON, and couple of VAl and ON. c The PDOS of AlN with VN defect that introduces two donor energy levels and an acceptor energy level in inner bandgap. d Energy band diagram describes the radiative transition mechanism of phosphorescence (Phosph.) with stable transition from N 2p orbit to N 2p + Al 3p orbit.