Observation of 1.5μm photoluminescence and electroluminescence from a holmium organic complex

Abstract

Electroluminescence (EL) and photoluminescence in both the visible and near-infrared spectral range were observed from a $\text{holmium}{\left(\text{dibenzoylmethanato}\right)}_3\left(\text{bathophenanthroline}\right)$ $\left[\mathrm{Ho}{\left(\mathrm{DBM}\right)}_3\text{bath}\right]$ . Five peaks at $580\mathrm{nm}$ , $660\mathrm{nm}$ , $980\mathrm{nm}$ , $1200\mathrm{nm}$ , and $1500\mathrm{nm}$ , respectively, were attributed to the internal $4f$ electronical transitions of the ${\mathrm{Ho}}^{3+}$ ions. Except for the emissions of the ${\mathrm{Ho}}^{3+}$ ions, a broadband exciplex emission from $480\mathrm{nm}\text{to}670\mathrm{nm}$ appeared in the EL cases. The emission intensity of the exciplex at organic interface showed a tendency to saturation beyond a certain driving voltage, while the emissions of the ${\mathrm{Ho}}^{3+}$ ions kept increasing. This evolution of visible EL spectra was discussed in terms of the extension of the charge recombination zone. The $1500\mathrm{nm}$ emission corresponding to the ${}^{5}F_5\to {}^{5}I_6$ transition suggests that the $\mathrm{Ho}{\left(\mathrm{DBM}\right)}_3\text{bath}$ is a potential candidate for optical communications.