A composite material, which can be used as an encapsulant for an ultraviolet device, is provided. The composite material includes a matrix material and at least one filler material incorporated in the matrix material that are both at least partially transparent to ultraviolet radiation of a target wavelength. The filler material includes microparticles and/or nanoparticles and can have a thermal coefficient of expansion significantly smaller than a thermal coefficient of expansion of the matrix material for relevant atmospheric conditions. The relevant atmospheric conditions can include a temperature and a pressure present during each of: a curing and a cool down process for fabrication of a device package including the composite material and normal operation of the ultraviolet device within the device package.