Multicolor upconversion reversible modulations in YNbO_(4):Er^(3+)/Tm^(3+)/Yb^(3+) photochromic materials

Photochromic materials with multicolor upconversion reversible modulations are attractive in optical switching devices.Herein,the fabricated YNbO_(4):Er^(3+)/Tm^(3+)/Yb^(3+) materials exhibit excellent photochromism and multicolor upconversion properties from green,red to near infrared(NIR) emissions with increasing Yb concentrations.Reversible multiband upconversion modulations are achieved by alternating light(365 and 405 nm) or thermal stimuli.After 365 nm irradiation,the luminescence color changes from yellow to red,the luminescent photoswitching contrast reaches up to 86.21%(green),82.12%(red) and 77.38%(NIR) in the Y_(0.83)Er_(0.01)Tm_(0.01)NbO_(4):0.15 Yb sample.Besides,the upconversion emission intensity before and after photochromic reaction shows remarkable change in a wide temperature range of 298-718 K.These results indicate that the Er^(3+)/Tm^(3+)/Yb^(3+) tri-doped YNbO_(4) materials can be a good candidate in optical switching and data storage applications.

A time-dependent luminescent phosphor of Na_(2)Ba_(2)Si_(2)O_(7):Eu for multi-level encryption and dynamic information display

Photo-stimuli responsive materials show great potential in the fields of information encryption and storage due to their distinctive spatial or temporal color changes.However,the conventional single or multi-color static outputs by light stimulus difficulty meet practical requirements for high-security optical storage technologies.Here,a novel dynamic irradiation-responsive phosphor of Na_(2)Ba_(2)Si_(2)O_(7):Eu is demonstrated,exhibiting high storage stability and convenient readout behaviors.The inherent Eu^(2+)luminescence can be dynamically tuned,instantly read out,and conveniently erased by controlling irradiation duration of a portable diode laser(365 nm).The modulation mechanism is unraveled by optically induced oxidation reactions of Eu^(2+)→Eu^(3+)and defects as killer centers.The excellent luminescence modulation degree(ΔR_(t)=89.5%)and the accompanying larger color contrast enable the creation of invisible optical codes with multi-level encryption in bright or dark field.These results indicate potential applications of Na_(2)Ba_(2)Si_(2)O_(7):-based materials in information encryption and invisible optical storage,and are expected to expand more investigations on optically induced PL modulation behaviors based on mixed valences and defects.

Exploration about superior anti-counterfeiting ability of Sm^(3+) doped KSr_(2)Nb_(5)O_(15) photochromic ceramics:Origin and atomic-scale mechanism

Reversible luminescence modulation behavior upon the photochromic effect endows the photochromic ceramics with 3reat potential in anti-counterfeiting and data storage applications.Here,Sm^(3+)-doped KSr_(2)Nb_(5)O_(15) photochromic ceramics exhibit superior anti-counterfeiting ability:good covertness and considerable modulation ratio of luminescent emission intensity after photochromic reaction.The results show that the photochromism originated from oxygen and cation vacancies,which were directly identified by electron paramagnetic resonance and positron annihilation lifetime spectra.Unexpectedly,oxygen vacancies work more effectively than cation vacancies during photochromic reactions.Moreover,the extraordinary anti-counterfeiting ability was attributed to the high energy transfer rate,which was particularly caused by the short mean distance below 1 nm between the Sm^(3+) and vacancies.The work here has provided atomic-scale structural evidence and made a progress in understanding the photochromic origins and mechanism in color-center theory.