Journal of Luminescence (2016)

Investigation of the quenching mechanisms of Tb3+ doped scheelites
Katrien W. Meert, Jonas J. Joos, Dirk Poelman, Philippe F. Smet
Journal of Luminescence 173 (2016) 263-273

The luminescence of terbium-doped lead tungstate (PbWO4:Tb3+) features not only emission from the 5D4 and 5D3 excited states of Tb3+, but also host and defect related broad emission bands are found. The blue host emission is attributed to the WO42βˆ’ centres whereas the green emission can be ascribed to WO3 defects. Upon host excitation, Tb3+ emission is observed pointing to energy transfer mechanisms between host and dopants. The electronic structure of Tb3+ defects inside the PbWO4 host are empirically deduced from optical and luminescence spectroscopy, both in steady-state as well as in time-resolved mode, as a function of temperature and doping concentration to asses the influence of key parameters in the energy transfer processes. The luminescence originating from Tb3+ ions shows a strong dependency on both the excitation wavelength and the temperature. For instance, an intensity increase in the 75–125 K range upon excitation via the WO42βˆ’ centres is found, which is absent for direct excitation. The undoped sample is characterized by a temperature-dependent energy transfer from WO42βˆ’ to WO3 defect centres with an thermal energy barrier of 0.26 eV. The divergent thermal quenching profiles of the host emission for pure PbWO4 versus doped materials reveal both a direct energy transfer and a temperature dependent energy transfer process from the host towards the Tb3+ ions. The emission efficiency of the 5DJ levels is investigated as well and a thermal quenching energy of 0.51 eV (J=3) and 0.86 eV (J=4) was found.

Keywords: Luminescence; Scheelite; Terbium; Thermal quenching; Energy transfer

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