Emission intensity of the $\lambda$ = 1.54 $\mu$m line in ZnO films grown by magnetron sputtering, diffusion doped with Ce, Yb, Er

The effect of the Er$^{3+}$-ion excitation type on the photoluminescence spectra of crystalline ZnO(ZnO$\langle$Ce, Yb, Er$\rangle$) films is determined in the cases of resonant ($\lambda$ = 532 nm, Er$^{3+}$-ion transition from ${}^4$S$_{3/2}$, ${}^2$H$_{11/2}$–${}^4$I$_{15/2}$) and non-resonant ($\lambda$ = 325 nm, in the region near the ZnO band-edge emission) excitation. It is shown that resonant excitation gives rise to lines with various emission intensities, characteristic of the Er$^{3+}$-ion intracenter 4$f$ transition with $\lambda$ = 1535 nm when doping crystalline ZnO films with three rare-earth ions (REIs, Ce, Yb, Er) or with two impurities (Ce, Er) or (Er, Yb), independently of the measurement temperature ($T$ = 83 and 300 K). The doping of crystalline ZnO films with rare-earth impurities (Ce, Yb, Er) leads to the efficient transfer of energy to REIs, a consequence of which is the intense emission of an Er$^{3+}$ ion in the IR spectral region at $\lambda_{\mathrm{max}}$ = 1535 nm. The kick-out diffusion mechanism is used upon the sequential introduction of impurities into semiconductor matrices and during the postgrowth annealing of the ZnO films under study. The crystalline ZnO films doped with Ce, Yb, Er also exhibit intense emission in the visible spectral region at room temperature, which makes them promising materials for optoelectronics.