Intense red upconversion luminescence in Er3+-sensitized particles through confining the 1532 nm excitation energy

Abstract

Lanthanide-doped upconversion (UC) materials are commonly excited by 700–1000 nm laser because of Yb3+ (980 nm excitation) and Nd3+ (808 nm excitation) are typically used as sensitizers. However, the excitation band located in the second near-infrared window (NIR-II, 1000–1700 nm) demonstrates the deeper penetration in biological tissue with minimum tissue scattering and autofluorescence. Herein, intense red UC emission in Er3+-sensitized NaLuF4 particles under 1532 nm NIR-II excitation is presented. Red UC luminescence is significantly enhanced and purified through confining the 1532 nm excitation energy by Ho3+ and Tm3+ mediators, via an energy back transfer pathway (Er3+ → Ho3+ → Er3+ and Er3+ → Tm3+ → Er3+). Furthermore, when the particles injected into the fresh beef, red UC luminescence can be distinctly observed from the inside of beef under 1532 nm NIR-II excitation, implying the deep penetration of 1532 nm NIR-II excitation and 660 nm red UC emission. Our results suggest that bright red UC luminescence from Er3+-sensitized NaLuF4 crystals with 1532 nm NIR-II excitation may be suitable for deep optical imaging.