OPTICAL-PROPERTIES OF NANOCRYSTALLINE SILVER-HALIDES

A review of quantum confinement effects in nanocrystals of silver brom ide (AgBr) and silver iodide (AgI) is presented. AgBr is an indirect g ap semiconductor while AgI has a direct band-to-band lowest energy tra nsition. An examination of the low-temperature optical properties of q uantum confined AgBr grown using a variety of synthetic techniques wil l be made. The dynamics of some of the involved excitonic processes wi ll be measured and discussed in reference to a possible breakdown in t he momentum selection rules as the nanocrystals are made smaller. Othe r explanations for this behavior such as impurity exclusion and surfac e effects will also be considered, as will the dynamics associated wit h the trapping of excitons at intrinsic iodide impurities in AgBr. Abs orption measurements on AgI nanocrystals will be discussed and compare d with the exciton photophysics in AgBr. Both AgBr and AgI display an increasing blue shift of their luminescence, arising from the recombin ation of excitons, as the crystallite size decreases. The luminescence intensity arising from this process increases with decreasing size in AgBr but it disappears in small crystals of AgI. This leads to the co nclusion that in the latter material nonradiative decay channels are o pening up as the size decreases.