Optical limiting characteristics and mechanism of silver bromide nanosols

Optical limiting behavior has been observed in nanosols comprising ∼60 Å particles of silver bromide. Switching times, τ, are consistently in the ns regime, and values of I1/2;, the pulse laser exposure which elicits a 50% decrease in transmittance of the medium, can be less than 20 mJ/cm2. Nonlinearity of response, I1/2, and response time all increase with decreasing pAg [Eq. (2)] of the nanosols. The materials can be cycled apparently indefinitely, provided they are subjected only to very short (sub-ns) laser pulses. Optical switching can be spectrally sensitized; comparable response parameters are obtained under these conditions. The nonlinear character of the response is, however, very different: a true response threshold, I0=∼12 mJ/cm2, is observed. Analysis of the optical limiting mechanism suggests that iodide doping, which is adventitious in the present case, is critical to the observed photophysical behavior of the nanosols.