Photonic crystals of coated metallic spheres

It is shown that simple face-centered-cubic (fcc) structures of both metallic and coated metallic spheres are ideal candidates to achieve a tunable complete photonic bandgap (CPBG) for optical wavelengths using currently available experimental techniques. For coated microspheres with the coating width to plasma wavelength ratio l_c/λ_p <= 10% and the coating and host refractive indices n_c and n_h, respectively, between 1 and 1.47, one can always find a sphere radius r_s such that the relative gap width g_w (gap width to midgap frequency ratio) is larger than 5% and, in some cases, g_w can exceed 9%. Using different coatings and supporting liquids, the width and midgap frequency of a CPBG can be tuned considerably.