Infrared-to-visible Eu³⁺ energy upconversion due to cooperative energy transfer from an Yb³⁺ ion pair in a sol-gel processed multi-component silica glass

Energy upconversion of Eu³⁺ is demonstrated in a sol-gel processed silica glass co-doped with Yb³⁺ ions. Yellow-orange emission is observed originating from the Eu³⁺ ions due to nonresonant cooperative energy transfer from pairs of excited Yb³⁺ ions when a diode laser emitting at a wavelength of 973 nm is used as an excitation source. The Yb³⁺-Eu³⁺ energy transfer rate is estimated as approximately 280 s^-1 based on an analysis of the Yb³⁺ infrared luminescence decay time.