Green light. On YCl[WO₄] as host material for luminescence active Tb³⁺ cations

Coarse, colorless and transparent single crystals as well as single phase powder of YCl[WO₄] were yielded by the reaction of Y₂O₃, YCl₃, and WO₃ in evacuated silica ampules at 850 C for six days, utilizing a fivefold excess of YCl₃ with respect to the stoichiometric ratio as flux. The title compound crystallizes isotypically to the RECl[WO₄] representatives for RE = Gd - Tm in the monoclinic space group C2/m (a = 1022.41(3), b = 722.91(2), c = 684.34(2) pm; β = 107.455(3) ; Z = 4). By doping the title compound with about 1 % Tb³⁺ cations, bright green luminescence is observed upon irradiation with UV light. Investigations of the excitation and emission spectra at room temperature as well as 77 K reveal a slight shift in the O^2- → W⁶⁺ LMCT transition towards shorter wavelengths upon reducing the temperature. This charge transfer transition can be used as sensitizer for the Tb³⁺ luminescence, however, the ⁵D₃ state of the latter is not reached by this excitation. This is possible by exciting the ⁷F₆ → ⁵G₆ transition, which causes the emissions from the aforementioned ⁵D₃ level to intensify, thus causing a blue shift of the emission. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)