Upconversion luminescence of Gd$_{2}$O$_{3}$ nanocrystals doped with Er$^{3+}$ and Yb$^{3+}$ ions

The upconversion luminescence (UCL) of nanocrystalline gadolinium oxide (Gd$_2$O$_3$) doped with Er$^{3+}$ and Yb$^{3+}$ ions has been studied in the temperature range of 90–400 K. The nanocrystals were synthesized by chemical vapor deposition and possessed a cubic crystalline structure with an average particle size within 48–57 nm. It is established that the USL intensity in the red ($^{4}F_{9/2}\to^{4}I_{15/2}$ transition in Er$^{3+}$ ion) and green ($^{4}S_{3/2}\to^{4}I_{15/2}$ transition) spectral regions depends on the sample temperature and concentration of dopant ions, as well as on the additional structural defects (anion vacancies) created in the crystal lattice by the introduction of Zn$^{2+}$ ions or irradiation with high-energy (10 MeV) electrons. The luminescence efficiency and spectrum of the upconversion phosphor are determined by energy transfer processes.