Evidence for Tm2+→Tm3+ energy transfer in Tm-doped BaCl2 for potential use in opto-electronic devices

The energy transfer from Tm 2+ to Tm 3+ , which has not yet been reported before, has now been observed for the first time. It was found that orthorhombic BaCl 2 :Tm 2+ ,Tm 3+ with the PbCl 2 cotunnite structure shows the luminescence properties to enable Tm 2+ →Tm 3+ energy transfer. Evaluation of the luminescence properties of BaCl 2 :Tm 2+ ,Tm 3+ in detail and other Tm 2+ /Tm 3+ -activated phosphors in general makes clear that the conditions for Tm 2+ →Tm 3+ energy transfer are a strong overlap of the Tm 2+ spin-allowed 4f 12 5d 1 →4f 13 emission with Tm 3+ 3 H 6 → 3 F 3 or 3 H 6 → 3 H 4 (4f 12 →4f 12 ) excitations or overlap of the Tm 2+ spin-forbidden 4f 12 5d 1 →4f 13 emission with Tm 3+ 3 H 6 → 3 H 4 (4f 12 →4f 12 ) excitation, resulting in both cases in interconfigurational transitions, while the Tm 2+ spin-allowed 4f 12 5d 1 →4f 13 emission should not overlap with the Tm 2+ spin-forbidden 4f 13 →4f 12 5d 1 excitation. In addition, the Tm 2+ -Tm 3+ distance has to be small, preferably for a high Tm 2+ concentration to increase the absorption of excitation radiation in combination with a low Tm 3+ concentration in order to avoid concentration quenching of the luminescence. Finally, implications of Tm 2+ →Tm 3+ energy transfer for applications such as luminescent solar concentrators are discussed. • First Observation of Tm2+→Tm3+ Energy Transfer • Tm2+→Tm3+ Energy Transfer in Tm-doped Orthorhombic BaCl2 • Prediction of Tm2+→Tm3+ Energy Transfer in Tm-doped Halides • Tm2+→Tm3+ Energy Transfer for Use in Opto-Electronic Devices • Tm-doped Orthorhombic BaCl2