Advanced information encryption strategy by gathering light and heat in negative thermal expansion ScZr(VO4)(WO4)2:Eu phosphors

Optical information encryption has critical importance for protecting property security, thus triggers great demands for exploring multi-color emission luminescence materials. In this work, we proposed a novel strategy for optical information encryption based on the thermal-responsive color-tunable emission phosphors. The information can be carried and enciphered by phosphors, then identified only by simultaneous heating and ultraviolet light irradiation, demonstrating higher security in the application. Given the thermal stability of luminescence and feasible regulation of emission spectra by temperature, we developed various concentrations of europium ions doped ScZr(VO 4 )(WO 4 ) 2 phosphors by introducing vanadate with self-excited emitting performance through co-substitution of [Zr 4+ -V 5+ ] for [Sc 3+ -W 6+ ] in Sc 2 W 3 O 12 negative thermal expansion phosphors. When the temperature increases from 298 K to 523 K, the lattice contraction can be observed due to the transverse vibration of bridging oxygen for [Sc/ZrO 6 ] octahedral and [W/VO 6 ] tetrahedron. As a result, the energy transfer efficiency from [VO 4 ] 3- to Eu 3+ is improved, and the spectra regulation is realized by different responses of green and red emissions to temperature. Under 275 nm excitation, the luminescence color of ScZr(VO 4 )(WO 4 ) 2 : 5 mol% Eu changes from green to white, to orange and to red. Moreover, the color-tunable performance is reversible for alternated heating and cooling cycles. To verify the practicality, simple experiments were designed and successfully executed. It is believed that the ScZr(VO 4 )(WO 4 ) 2 : Eu phosphors can be promising candidates for optical information encryption.