Relationship between photochromism and persistent luminescence in barium-magnesium silicates

Photochromism and persistent luminescence (PersL) are two fascinating light-responsive effects in phosphors, both of which have found widespread applications in optical switching, optical anticounterfeiting and information storage. However, the relationship between photochromism and PersL has not been clarified, thus greatly limiting the use and design of the light-responsive materials in multifunctional applications. Herein, taking BaMgSiO4:Eu2+, TM (TM = transition metal: Fe, Co and Cr) as model materials, we first reveal that photochromism and PersL could be two independent photophysical effects, although they are both related to the charge carrier trapping/detrapping processes. Notably, photochromism and PersL show have different responses to light wavelengths, and the depth of traps involved in the two effects is also quite different. Moreover, by codoping different transition metal elements, we obtain the largest reflectance difference of ∼71 % among inorganic photochromic materials reported thus far, and demonstrate interesting multicolor photochromism, including magenta, golden and pink. Based on their distinct response to light and temperature, a multi-functionalized optical anticounterfeiting technology is proposed, which may open up a new avenue for applying the light-responsive materials in flexible electronics and wearable devices.