Boron Nitride Nanoparticle Phosphors for Use in Transparent Films for Deep-UV Detection and White Light-Emitting Diodes

White-emitting hexagonal boron nitride (h-BN) nanophosphors were synthesized via pyrolysis (1200 °C). The nanoparticle phosphors were prepared by chemical mixed molecular adduction in which the starting materials were boric acid, melamine, cerium nitrate (Ce3+), and dysprosium nitrate (Dy3+). The nanoparticle phosphors showed blue-yellow emission activated by attendant incorporation of Ce3+ and Dy3+ when excited under ultraviolet (UV) light. This color emission was modified from blue to yellow by adjusting the atomic ratio of rare earth elements ([Dy+]/[Ce3+]) without interruption of the crystal structure of h-BN. Photoluminescent (PL) intense yellow emission was realized in BN:Ce3+/Dy3+ phosphors at [Dy+]/[Ce3+] = 0.5, and the characteristic Ce3+ emission peaks of 4f–5d at 480 nm and Dy3+ due to the transitions of 4F9/2 → 6H15/2 at 480 nm, 4F9/2 → 6H13/2 at 575 nm, and 4F9/2 → 6H11/2 at 662 nm were observed in the PL emission spectra. However, further addition of Dy3+ ions exchanged the phase in h-BN to dysprosium borate (DyBO3), according to X-ray diffraction results, and decreased luminescence properties, according to PL findings. In addition, the synthesized nanophosphors showed white emission under UV light for thin films that would be suitable for deep-UV detection and anti-counterfeiting applications, which require the film to be hidden and identifiable only by macroscopic examination. In addition, the co-doped nanophosphors can be applied to white-emitting LED glass discs.