Hexagonal boron nitride (hBN), which is conventionally used as one of the best-known heat-resistant materials due to its high thermal and chemical stability, has recently been found as a highly luminous material in the far-ultraviolet (FUV) region. This paper reviews the recent studies of hBN growth, optical properties, and device application development. In the case of highly pure crystals of hBN grown by the solvent growth method, the electronic excitation states near the band gap are governed by optically allowed exciton effects, which originate from the Jahn–Teller effect on the exciton series. The excitonic luminescence bands are utilized for an FUV plane light-emitting device excited by field emitters to take advantage of the highly luminous character.