Infrared upconversion in radio frequency magnetron sputtered Er-doped zinc oxide thin films.

Upconversion in radio frequency magnetron sputtered Er-doped zinc oxide thin films on Si substrate has been demonstrated using 1550 nm cw laser excitation. As-sputtered thin films did not show any upconversion emission, and annealing was required to optically activate the Er³⁺-ions. Emissions at 985, 809, and 665-675 nm were observed in annealed thin films, corresponding to transitions from ⁴I_11/2, ⁴I_9/2, and ⁴F_9/2 to the ground state ⁴I_15/2, respectively. The emission from ⁴I_11/2 was the dominant one, whereas emission from ⁴I_9/2 was the weakest. The highest intensity at 985 nm was obtained with 2.4 at.% of Er by annealing the film at 700 ℃. Annealing at higher temperatures causes Er to diffuse and segregate to the Si-ZnO interface between the Si substrate and the ZnO film. [ABSTRACT FROM AUTHOR]