Optical and photoemission studies of TmTe

We report here on the optical absorption of TmTe films ($5<T<300$ K; 0.2<hν<4.5 eV) and the reflectance (0.2<hν<20 eV) and ultraviolet photoemission spectra (UPS; 15≤hν≤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 Tm²⁺, e.g., the first absorption band centered at 0.7 eV is identified as due to a transition from Tm²⁺ 4f¹³→4f¹²(³H₆)5d(t2g). No optical structure was seen which would permit us to identify Tm³⁺ in TmTe. The UPS data show a small amount of Tm³⁺ which was, however, strongly influenced by surface conditions in spite of in situ study in a vacuum of 10^-10 Torr. We conclude that Tm is essentially divalent in TmTe.