EFFECTIVE-MEDIUM THEORY CHARACTERIZATION OF AU AG NANOALLOY POROUS ALUMINA COMPOSITES/

The optical constants n(Al) and k(Al) of a 50/50 volume fraction Au/Ag alloy were derived synthetically by application of a Bruggeman (BG) e ffective medium expression. The alloy data base was then input into a Maxwell-Garnett (MG) effective medium expression to determine the abso rption maximum of the nano-alloy/insulator composite (the volume fract ion of the nano-alloy was equal to 5%). The absorption maximum (lambda (max)) of the hypothetical composite was found to be 499 nm for spheri cal particles and was blue-shifted relative to that of a composite con taining pure gold nanospheres (499 vs. 528 nm respectively). The trans mission color at this wavelength was a red-orange. lambda(max) in the range 512 to 519 nm (Au/Ag alloy between 60/40 - 70/30 volume fraction respectively) is needed to obtain the scarlet-red exhibited by the fa mous Lycurgus cup of 4th century Rome (1). (C) 1997 Acta Metallurgica Inc.