Ultraviolet optical excitation of near infrared emission of Yb-doped crystalline aluminum oxynitride thin films

Yb³⁺ ions hold promises for high power emission in the near infrared (NIR). Yet, relevant matrices, comprising mediators to excite Yb³⁺, have to be found and the optical mechanisms have to be studied in detail. The purpose of this study is to report on the optical excitation and emission mechanisms of NIR photoluminescence (PL) of Yb-doped crystalline aluminum oxynitride thin films prepared at room temperature using reactive magnetron sputtering. Crystal structure and chemical composition are analyzed by transmission electron microscope and Rutherford backscattering spectrometry, respectively. Photoluminescence spectroscopies are used to investigate the excitation and emission mechanisms. NIR emission at 985 nm is obtained under indirect optical excitation using the 325 nm line of a He-Cd laser, the excitation mechanism is explored by photoluminescence excitation measurement (PLE), and the fine structure of the emitted energy levels is investigated by performing PL measurements at low temperature (LTPL). PLE shows that the host defects play the role of mediators to transfer the excitation energy to Yb ions. This offers different possibilities for the development of multiple excitation channels for Yb³⁺. Stark splitting of the energy levels of the ²F_5/2 and ²F_7/2 transitions is evidenced using LTPL in the 78 to 295 K range. Electronic transitions are ascribed to experimental emission lines based on good agreement with theoretical values. Moreover, the activation energies for PL thermal quenching are determined and correspond to the energy difference between highest energy quenched lines and thermally activated “hotlines.”