Thermal quenching of Eu2+ emission in Ca- and Sr-Ga2S4 in relation with VRBE schemes
AP Dobrowolska (Wroclaw University of Economics and Business, TU Delft - RST/Fundamental Aspects of Materials and Energy)
Benjamin Dierre (TU Delft - RST/Fundamental Aspects of Materials and Energy)
C.M. Fang (Brunel University)
H. T. Hintzen (TU Delft - RST/Fundamental Aspects of Materials and Energy)
P. Dorenbos (TU Delft - RST/Fundamental Aspects of Materials and Energy)
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Abstract
Structural and optical properties of MGa2S4 (M = Mg, Zn, Ca, Sr, Ba) compounds have been compared, and the vacuum referred binding energy (VRBE) schemes were constructed for the lanthanide ions in the iso-structural compounds CaGa2S4 and SrGa2S4 employing literature data. The VRBE of an electron in the 5d excited state of Eu2+ was found at 0.75 and 0.97 eV below the bottom of the conduction band (CB) in CaGa2S4:Eu and SrGa2S4:Eu, respectively. Such differences explains the unexpected higher thermal quenching temperature reported for Eu2+-doped SrGa2S4 (T50% = ∼475 K) compared to Eu2+-doped CaGa2S4 (T50% = 400 K) The significantly lower VRBE at the CB-bottom in CaGa2S4 versus SrGa2S4 may be explained by the shorter Ga-S bond lengths in SrGa2S4.
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