Abstract :
Photoluminescence excitation spectroscopy (PLE) studies have been performed for spark-processed Si (sp-Si), which exhibited intense PL in the UV/blue spectral range peaking at 400 nm (3.1 eV) and a green luminescence peak near 525 nm (2.36 eV). A broad absorption band was observed at 5 eV (248 nm), 4.2 eV (295 nm), and 3.6 eV (344 nm). Furthermore, a relatively low energy narrow absorption band was detected at 2.7 eV (459 nm) and 2 eV (620 nm). These absorption bands determined by PLE studies enabled us to clearly understand a PL peak position dependence on laser excitation energy for both blue and green luminescence sp-Si. Specifically, the blue and green photoluminescence peaks of sp-Si, which were detected by the excitation of 325 nm (3.81 eV) He–Cd laser, were interpreted to originate from energy levels at 3.6 eV (344 nm) into 3.22 eV (385 nm) and 2.36 eV (525 nm) via non-radiative transition. At that point electrons reverted to ground state by a radiative transition. In contrast, an Ar+ laser excitation pumped electrons into a closely spaced lower energy absorption band at 2.0 eV (620 nm), and thus resulted in only a 1.9 eV (650 nm) radiation.
