Evidence for Tm2+→Tm3+ energy transfer in Tm-doped BaCl2 for potential use in opto-electronic devices
M. P. Plokker (RWE Generation, TU Delft - RST/Luminescence Materials)
S. W. Bergkamp (Student TU Delft)
H. T. Hintzen (TU Delft - RST/Luminescence Materials)
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Abstract
The energy transfer from Tm2+ to Tm3+, which has not yet been reported before, has now been observed for the first time. It was found that orthorhombic BaCl2:Tm2+,Tm3+ with the PbCl2 cotunnite structure shows the luminescence properties to enable Tm2+→Tm3+ energy transfer. Evaluation of the luminescence properties of BaCl2:Tm2+,Tm3+ in detail and other Tm2+/Tm3+-activated phosphors in general makes clear that the conditions for Tm2+→Tm3+ energy transfer are a strong overlap of the Tm2+ spin-allowed 4f125d1→4f13 emission with Tm3+ 3H6→3F3 or 3H6→3H4 (4f12→4f12) excitations or overlap of the Tm2+ spin-forbidden 4f125d1→4f13 emission with Tm3+ 3H6→3H4 (4f12→4f12) excitation, resulting in both cases in interconfigurational transitions, while the Tm2+ spin-allowed 4f125d1→4f13 emission should not overlap with the Tm2+ spin-forbidden 4f13→4f125d1 excitation. In addition, the Tm2+-Tm3+ distance has to be small, preferably for a high Tm2+ concentration to increase the absorption of excitation radiation in combination with a low Tm3+ concentration in order to avoid concentration quenching of the luminescence. Finally, implications of Tm2+→Tm3+ energy transfer for applications such as luminescent solar concentrators are discussed.
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