Multiple anti-counterfeiting strategy by integrating up-conversion,down-shifting luminescence, phosphorescence and photochromism into Na YTiO4: Bi/Er phosphors

With the rapid development of science and technology,the high-security-level anti-counterfeiting technique is essential for ensuring property or information security.In this work,we prepared micron NaYTiO_(4):Bi/Er(NYT:Bi/Er) phosphors with integrating up-conversion(UC) photoluminescence,downshifting(DS) emission,phosphorescence and photochromism(PC) performances for advanced multiple anti-counterfeiting application.Owing to the abundant energy levels of Er^(3+)ions,the UC and DS luminescence behaviors are anticipated.Specifically,the yellow-green emission of Er^(3+)ions can be observed upon 980 nm excitation,and the bright green emission is demonstrated under 281 or 254 nm excitation due to the energy transitions of Er^(3+)ions and the energy transfer process from Bi^(3+)to Er^(3+)ions.Besides,the introduction of Bi^(3+)ions generates defect levels in the matrix and thus leads to phosphorescence.Furthermore,the repeatable PC performance could be triggered by the 365 nm irradiation and vanished with 450 nm illumination or thermal stimulation.To verify the practical usability of NYT:Bi/Er phosphors on anti-counterfeiting applications,some experiments are designed and successfully executed.It is believed that the NYT:Bi/Er phosphors can be a promising candidate for high-security-level multiple anti-counterfeiting.