Tunable color emission of transparent boron nitride nanophosphors towards anti-counterfeiting application

Abstract

Water-dispersible transparent nanophosphors based on boron nitride nanoparticles were prepared by pyrolysis of boric acid-melamine molecular adduct. Intense blue-green emission was activated by concomitant incorporation of Ce3+ and Tb3+ when excited by near-UV light. Color emission from the nanophosphor was modified from blue to green by tuning atomic ratio of Ce3+ and Tb3+ without disturbance of crystal structure of hexagonal boron nitride. The intense green emission with high quantum efficiency (∼0.74) was realized in BN: Ce3+,Tb3+ phosphors at [Tb3+]/[Ce3+] = 0.62. However, further addition of Tb3+ ions induced formation of non-luminescent TbBO3 phase and mitigation of luminescence intensity. From the steady state and time-resolved photoluminescence spectra, the luminescence of Ce3+ was quenched with Tb3+ by energy transfer process of efficiency approaches to unity. Transparent thin films were deposited from aqueous colloidal solution of nanophosphors on various substrates to demonstrate high transparency of phosphor thin films feasible to anti-counterfeiting application which requires concealment and identification by naked eyes. Extreme sustainability of nanophosphors in high temperature environment was also confirmed from thermal treatment at 1200 °C for 5 h in air.