Optical and photoemission studies of TmTe

We report here on the optical absorption of TmTe films ($5<T<\mathrm{}300\mathrm{}$ K; $0.2<h\nu <4.5\mathrm{}$ eV) and the reflectance ($0.2<h\nu <20\mathrm{}$ eV) and ultraviolet photoemission spectra (UPS; $15\le h\nu \le 90$ eV) of vacuum- and air-cleaved TmTe single crystals. Much of the structure seen in absorption and reflectance spectra can be attributed to transitions from ${\mathrm{Tm}}^{2+}$, e.g., the first absorption band centered at 0.7 eV is identified as due to a transition from ${\mathrm{Tm}}^{2+}$ $4f^{13}\to 4f^{12}\left({}_{}{}^3{}_{}{}^{}H_6^{}{}_{}{}^{}\right)5d\left(t_{2g}\right)$. No optical structure was seen which would permit us to identify ${\mathrm{Tm}}^{3+}$ in TmTe. The UPS data show a small amount of ${\mathrm{Tm}}^{3+}$ which was, however, strongly influenced by surface conditions in spite of in situ study in a vacuum of ${10}^{-10\mathrm{}}$ Torr. We conclude that Tm is essentially divalent in TmTe.