Er³⁺/Yb³⁺ - activated silica–hafnia planar waveguides for photonics fabricated by rf-sputtering

The spectrum of Figure 1 shows the emission band located at 1500 nm due to the emission of erbium ions, and the emission band with a peak at 978 nm and a smaller peak at 1010 nm, typical of the ytterbium ion emissions in glasses. This pattern is an indication of the presence of the back energy transfer from Er³⁺ to Yb³⁺ ions. In fact, using the 514.5 nm laser line we excite directly only the Er³⁺ ions but an emission relative to the ²F_5/2→²F_7/2 transition of Yb³⁺ is observed. Nevertheless, the PL excitation spectra reported in figure 2 indicates that an effective energy transfer from Ytterbium to Erbium ions is present. In fact, as reported in Figure 2, the spectral shape of the excitation spectrum corresponds of the sample co-activated with Ytterbium ions to the typical Ytterbium absorption.

Infrared-to-visible CW frequency upconversion in erbium activated silica–hafnia waveguides prepared by sol–gel route

The value of the slope n, obtained by fitting the measured upconversion intensity as a function of the excitation power, indicates that two photons are involved in the infrared-to-green and three photons are involved in the infrared-to-blue upconversion processes.

Energy level diagram and the proposed mechanism for the red emission observed in Er³⁺-activated 70SiO₂-30HfO₂ waveguides, upon excitation at 980 nm. The upward solid arrows represent excitation by GSA, ESA or ETU mechanisms. The downward solid arrows indicate the red upconverted emission, and the dashed arrows represent cross-relaxation (CR) between the A and B ions.

Down-converter based on rare earth doped fluoride glass to improve Si-based solar cell efficiency

Efficient down-conversion bulks Pr³⁺-Yb³⁺ co-doped ZLAG glasses have been developed. Emission of the ytterbium at 980 nm was observed after excitation of the praseodymium at 476 nm. We evaluated the energy transfer efficiency for the ³P₀ state of the praseodymium to the ytterbium ions for the first step of the quantum cutting process. We observed an increase of the energy transfer efficiency with the concentration of ytterbium ions. The sample with 0.5 mol% of praseodymium and 10 mol% of ytterbium presents an energy transfer efficiency of 92%, similar to the best results obtained in fluoride crystals with the same doping.