As　an　emerging　2D　ultrawide　bandgap　semiconductor,　hexagonal　boron　nitride　(h-BN)　is　gaining　significant　attention　for　its　superior　properties　and　wide　applications.　Although　optical　properties　of　h-BN　have　been　partially　revealed　by　using　h-BN　bulk　single　crystal,　luminescence　properties　of　the　h-BN　few-layer　are　rare　due　to　its　poor　crystallinity.　In　this　work,　the　h-BN　epilayers　have　been　synthesized　on　sapphire　substrates　by　the　submicron-spacing　vapor　deposition　method.　The　crystalline　quality　of　the　h-BN　epilayer　is　improved　with　the　increase　of　the　growth　temperature,　and　the　full　width　at　half-maximum　of　the　Raman　peak　is　only　&　AP;13　cm(-1).　The　low　temperature　cathodoluminescence　spectra　of　h-BN　epilayers　exhibit　two　strong　deep　ultraviolet　(DUV)　luminescence　peaks　at　5.49　and　5.35　eV,　as　well　as　a　weaker　and　broader　defect-related　emission　band　at　&　AP;4.0　eV.　The　DUV　emission　band　is　ascribed　to　the　recombination　of　bound　excitons　and　its　phonon　replica.　Based　on　the　theoretically　predicted　energy　levels,　the　4.0　eV　emission　band　is　tentatively　attributed　to　the　radiative　transition　from　C　impurities　occupying　the　B　sites　to　the　B　vacancies.　Moreover,　the　h-BN-based　DUV　photodetectors　exhibit　an　outstanding　performance,　making　it　a　promising　prospect　for　optoelectronic　applications.