While high-purity hexagonal boron nitride monocrystal (hBN) obtained by way of a high temperature/high-pressure treatment in the presence of a high-purity solvent has excellent properties in terms of far-UV luminescence characteristics, it has drawbacks including that it can be easily adversely affected by mechanical vibrations and impetus, that monocrystal shows a poor morphological retentiveness and that the luminescence characteristics fluctuate to shift the selected and set wavelength. The present invention can overcome the drawbacks of being easily affected by vibrations and showing a poor morphological retentiveness by grinding down the monocrystal obtained by a solvent/refining process into powder and applying the powder to a light emitting surface. Thus, the present invention provides crystal powder to be used for a far-UV luminescence device showing excellent luminescence characteristics that are stable and do not fluctuate.