Influence of Gold Nanoparticles on Luminescence of $\mathrm{Eu^{3+}}$ Ions Sensitized by Structural Defects in Germanate Films

Abstract

This investigation shows new possibilities of gold nanoparticles using for rise of Ln$^{3+}$ ions luminescence in oxide matrixes at ultraviolet synhrotron’s excitation on example of germanate films doped with Eu and Au. It has been established that formation of gold nanoparticles (AuNPs) in such films leads to the enhancement of the Eu$^{3+}$ ions luminescence intensity by many times at excitation in broad absorption bands having λ$_{max}$ about 120 and 180 nm. The discovered effect is explained by joint influence of the following factors: (1) rise in the nonbridging oxygen hole centers (NBOHCs) concentration as a result of breakage of the O–Eu bonds in the ≡Ge–O–Eu= bridges by the forming AuNPs; (2) nonradiative transfer of excitations from excitons to these centers; (3) effective sensitization of the Eu$^{3+}$ ions luminescence by the centers via the charge transfer (CT) state of the O$^{2–}$ + Eu$^{3+}$ complexes; (4) increase in the optical path of the exciting radiation due to the intensification of light scattering by the AuNPs, and, possibly, (5) promoting by the AuNPs of excitations transfer in the exciton −NBOHC–(O$^{2–}$ + Eu$^{3+}$) system in the nanoparticles field as well as weakening of reverse passivation of the hole centers by the hydrogen atoms formed on the breakage of the end OH– groups under the action of UV radiation