  Light propagation in a medium made of densely packed dielectric spheres is
investigated by using a rigorous diffraction theory. It is shown that a
substantial suppression of the local density of states occurs in spectral
domains where the single constituents exhibit Mie resonances. The local density
of states decreases exponentially at the pertinent frequencies with a linearly
increasing spatial extension of the aggregated spheres. It is shown that a
self-sustaining random arrangement of core-shell spheres shows the same
fundamental characteristics. Such approach offers a path towards easy to
fabricate photonic materials with omnidirectional gaps that may find use in
various applications.
