We have investigated the photoluminescence properties of beta-FeSi2 and have subsequently reported many studies on the enhancement of luminescence efficiency. We have further discussed a limit for the luminescence efficiency based on the weak confinement theory of excitons in beta-FeSi2 nanocrystals. Moreover, we have reported an application of beta-FeSi2 with a high refractive index to photonic crystals. (C) 2008 Elsevier B. V. All rights reserved.