Pure　and　defect-free　hexagonal　boron　nitride　(hBN)　nanocrystals　with　deep-ultraviolet　light　emissions　at　around　215nm　were　prepared　via　a　solid　state　reaction.　This　involved　preparing　a　precursor　from　potassium　borohydride　and　ammonium　chloride　powders,　and　then　heating　the　precursor　and　additional　ammonium　chloride　to　1000　°C　within　a　nitrogen　atmosphere.　The　hBN　nanocrystals　were　studied　using　a　variety　of　characterization　techniques　(e.g.,　TEM,　AFM,　N2　absorption/desorption).　A　growth　mechanism　based　on　size-dependent　oriented　attachment　was　proposed　for　the　nanocrystals.　©　2011　IOP　Publishing　Ltd.