Effect of Tm-Er concentration ratio on the photoluminescence of Er-Tm:Al₂O₃ thin films fabricated by pulsed laser deposition

Er-Tm codoped amorphous aluminum oxide (a-Al₂O₃) thin films have been prepared by an alternative pulsed laser deposition. The phase structure and the surface of the deposited thin films were characterized by the X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Effective photoluminescence (PL) in the region of 350-900 nm was observed when pumped at 325 nm, and the PL performance has been improved by modifying the Tm³⁺ concentration. With the increasing of [Tm]/[Er] concentration ratio, the intensity of emission of 382 nm and 500 nm bands was improved effectively while that of 765 nm band increased smoothly. Our results suggest that the resonant energy transfer and cross relaxation between Tm³⁺ and Er³⁺ play an important role in the evolution of the luminescent response.