Quantum efficiency of up-converting SrGd2O4:Yb,Er nanoparticles

Abstract

Up-conversion properties of SrGd2O4 nanoparticles co-doped with different Yb3+ and constant Er3+ ions were successfully prepared via sol- gel assisted combustion. Rietveld refinement and scanning/transmission electron microscopy with corresponding energydispersive X-ray spectroscopy revealed that obtained powders are composed of agglomerated nanoparticles with orthorhombic (Pnma) structure that have a uniform distribution of all constituting elements. Photoluminescence measurements implied intensification of the upconversion (UC) emission in the visible part of spectrum with the increase of Yb3+ content, which is followed by a significant change in the green to red ratio. Two-photon UC processes are established as a result of Er3+ f-f electronic transitions: green emission at 523 and 551 nm (2H11/2, 4S3/2 → 4I15/2) as well as a red emission at 661 nm (4F9/2 → 4I15/2). The highest value of absolute quantum efficiency (0.055%) is determined for SrGd2O4 nanoparticles doped with 0.5 at% of Er3+ and co-doped with 5 at% of Yb3+ (λexc=976 nm, power density 200W/cm2).