Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. Examples include gallium, ytterbium, bismuth and neptunium. Examples include gallium, ytterbium, bismuth, mercury and neptunium. The chemical behavior of ytterbium is similar to that of the rest of the lanthanides. Erbium and ytterbium ions are common active species in such lasers. Some ytterbium halides are used as reagents in organic synthesis. It is most often recovered commercially from monazite sand (0.03% ytterbium). A fourth oxide, ytterbium oxide, was isolated in 1878 by Jean Charles Galissard de Marignac. Finely dispersed ytterbium readily oxidizes in air and under oxygen. In 2015, the atomic weight of ytterbium was updated. Ytterbium metal increases its electrical resistivity when subjected to high stresses. The model with one single ytterbium ion caught in an ion trap is highly accurate. Later spectroscopic work found that the electron configuration of ytterbium was in fact [Xe]4f6s. Mixtures of powdered ytterbium with polytetrafluoroethylene or hexachloroethane burn with a luminous emerald-green flame. They used an electric field to trap an "Ion" of the element, Ytterbium.