Triboluminescence of trivalent rare earth ions inserted in polycrystalline zinc oxide

The room temperature triboluminescence of Er3+, Eu3+, Ho3+, Sm3+ and Tm3+ ions in the 400–850 nm range was observed during the abrasion of sintered polycrystalline ZnO samples containing the rare earth (RE) sesquioxides. The triboluminescence spectra are compared with the electro- and photoluminescence spectra of the pellets of the same composition and sintered under the same conditions. The tribo- and electroluminescence spectra show only the sharp lines characteristic of transitions between the 4f levels of the RE3+ ions whereas the photoluminescence spectra show only the broad ZnO emission. It is concluded that the triboluminescence of the RE3+ ions is consecutive to a direct electrical excitation, consequence of a breakdown in the RE3+-rich intergranular material.