Photobrightening of CuBr nanocrystals in PMMA

The photoluminescence (PL) intensity and its decay time of CuBr nanocrystals (NCs) embedded in poly methyl methacrylate increase with increasing the exposure time of the excitation light at 77 K. The PL intensity becomes smaller with increasing applied electric field, and returns to the initial one as soon as the electric field is cut. From these results, we propose a mechanism that an electron and a hole are generated inside the NC by light, and then, either of them goes out of the NC to neutralize a charged center outside the NC. On the other hand, the photodarkening effect by an applied electric field may be caused by the neutralization of the ionized centers inside the NC. (C) 2000 Elsevier Science B.V. All rights reserved.