Mutual quenching of Er photoluminescence under two laser excitation in GaN:Er

Erbium photoluminescence in GaN:Er was studied with above-band-gap excitation, provided by a He–Cd laser and below-band-gap excitation by a tunable Ti–Sa laser. The spectra obtained with these two lasers exhibit different spectral shapes. When both lasers are used at the same time, we observe that the Er³⁺ photoluminescence induced by each of the lasers is partly quenched by the illumination of the other laser. In this experiment, one of the lasers is modulated and a lock-in amplifier is used to filter the corresponding photoluminescence signal. The spectra recorded this way are found to be linear combinations of spectra obtained with each of the lasers used separately. This effect is explained by the presence of defects mediating the excitation towards the Er³⁺ ions. These defects act as electron traps, which can be populated by one specific laser excitation and are photo-ionized by the other laser leading to a large quenching of Er³⁺ emission.