Reversible dynamic modulation of orthogonal upconversion luminescence via interplay of oxygen vacancies and lanthanide activators

Dynamic modulation of upconversion (UC) luminescence with spatial-temporal spectral feature holds pivotal importance for optical multiplexing in anti-counterfeiting applications. Despite considerable efforts, achieving reversible dynamic UC emissions in a simple nanostructure with a fixed composition under external stimulation remains a daunting challenge. Here, we report temporal modulation of orthogonal UC luminescence in Er ³⁺ -doped bismuth halide oxides (BiOX, X = Cl, Br and I) by employing interplay of oxygen vacancies and erbium activators. Through alternating stimulation of ultraviolet irradiation and water bleaching, orthogonal UC luminescence of Er ³⁺ emitters could be reversibly regulated with high switching contrast and good fatigue resistance. Experimental and theorical results reveal that the introduction of oxygen vacancies and activators as well as their interactions contributes to the photochromism-induced dynamic UC modulation. Inspired by their special luminescent performance, the developed materials facilitate evolutionary UC color/intensity displays in both spatial and temporal dimensions under external manipulation, indicating promise in advanced anti-counterfeiting and high-capacity optical storage. Our findings offer a new way for dynamic manipulating of UC luminescence via external stimuli towards high-level anti-counterfeiting applications.