Up-conversion effect of Er- and Yb-doped ZnO thin films

Abstract

Visible up-conversion in ZnO:Er and ZnO:Er:Yb thin films deposited by RF magnetron sputtering under different O 2 -rich atmospheres has been studied. Conventional photoluminescence (325 nm laser source) and up-conversion (980 nm laser source) have been performed in the films before and after an annealing process at 800°C. The resulting spectra demonstrate that the thermal treatment, either during or postdeposition, activates optically the Er 3+ ions, being the latter process much more efficient. Moreover, the atmosphere during deposition was also found to be an important parameter, as the deposition under O 2 flow increases the optical activity of Er +3 ions. In addition, the inclusion of Yb 3+ ions into the films has shown an enhancement of the visible up-conversion emission at 660 nm by a factor of 4, which could be associated to either a better energy transfer from the 2 F 5/2 Yb level to the 4 I 11/2Er one, or to the prevention of having Er 2 O 3 clustering in the films.2

Activation of visible up-conversion luminescence in transparent and conducting ZnO:Er:Yb films by laser annealing

“…Therefore, the 325-nm laser → excitation should not be able to produce such effects. Nevertheless, a possible energy transfer can take place from the host matrix to the integrated ions, which is translated into their excitation [5,26]. As observed in Fig.…”

“…In particular, Er and Yb co-doped systems [2][3][4] have the capability to cooperate together to convert infrared radiation into visible light because of their energy levels matching for λ = 980 nm [5]. Yb species act as the absorber ions due to their higher absorption coefficient, thus absorbing the incoming low-energy photons (980 nm), whereas Er species act as the emitter ions, releasing higher-energy photons (550 nm, 660 nm, etc.)…”

Structural and optical properties of Al-Tb/SiO2 multilayers fabricated by electron beam evaporation

“…33 Actually, Tb 3þ requires a C 4V symmetry (a TbO 6 conformation) to be optically active, as in the case of other RE ions in the same oxidation state (such as Er 3þ or Yb 3þ ). [34][35][36] This occurrence, bearing in mind the multilayer structure, can take place at the interfaces between the Al/Tb mixed stack and the SiO 2 sublayers, although the possible diffusion of oxygen from the SiO 2 sublayers to the Al/Tb stack cannot be discarded; this argument also holds for the samples containing no Al. The fact that Tb 3þ ions are very sensitive to the presence of surrounding defects constitutes a drawback for their emission.…”

Strong enhancement of ultra-violet emission by Ce doping of ZnO sputtered films

“…In theoretical models, oxygen plays an important role in obtaining high quality ZnO films [8,9], and incorporating dopants can influence point defect concentrations and reactions. From a different perspective, rare earths (REs) doping of ZnO have been widely studied lately for potential applications [10][11][12][13][14][15], and the results are still debated. Ce doping of pyrolytic ZnO films have shown 3rd harmonic generation and promise for non-linear optics applications [16].…”