Experimental and numerical analysis of Tm2+ excited-states dynamics and luminescence in CaX2 (X = Cl, Br, I)
M. P. Plokker (TU Delft - RST/Luminescence Materials)
I.C. van der Knijff (TU Delft - Optical Technologies)
A.V. de Wit (Student TU Delft)
B. Voet (Student TU Delft)
T. Woudstra (Student TU Delft)
V. Khanin (TU Delft - RST/Luminescence Materials)
P. Dorenbos (TU Delft - RST/Luminescence Materials)
Erik van der Kolk (TU Delft - RST/Luminescence Materials)
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Abstract
The prospect of using Tm2+-doped halides for luminescence solar concentrators (LSCs) requires a thorough understanding of the temperature dependent Tm2+ excited states dynamics that determines the internal quantum efficiency (QE) and thereby the efficiency of the LSC. In this study we investigated the dynamics in CaX2:Tm2+ (X = Cl, Br, I) by temperature- and time-resolved measurements. At 20 K up to four distinct Tm2+ emissions can be observed. Most of these emissions undergo quenching via multi-phonon relaxation below 100 K. At higher temperatures, only the lowest energy 5d–4f emission and the 4f–4f emission remain. Fitting a numerical rate equation model to the data shows that the subsequent quenching of the 5d–4f emission is likely to occur initially via multi-phonon relaxation, whereas at higher temperatures additional quenching via interband crossing becomes thermally activated. At room temperature only the 4f–4f emission remains and the related QE becomes close to 30%. Possible reasons for the quantum efficiency not reaching 100% are provided.
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