High pressure studies of luminescence efficiency and lifetime in La2O2S:Eu and Y2O2S:Eu

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Abstract
The effect of pressure to 120 kbars has been measured on the luminescence efficiency of La2O2S:Eu and Y2O2S:Eu in concentrations from 0.1% to 3% europium. Lifetimes were also measured for the lanthanum compounds. For La2O2S:Eu the emissions from 5D0 and 5D1 decreased in intensity with increasing pressure; the very weak 5D2 emission increased by a large factor, leveled in the region ∼40–80 kbars and decreased at the highest pressure; the emission fro 5D3 appeared at about 50–60 kbars and increased rapidly in intensity. These results could be explained essentially quantitatively in terms of the analyses of Struck and Fonger and the observed shift to higher energy of the charge transfer absorption. Increased concentration of dopant dampened the effect of pressure. This is also consistent with the analysis. In addition, the behavior of the lifetime with pressure confirmed the above results and showed that no significant new radiationless paths appear at high pressure. There were also large pressure effects in Y2O2S:Eu. While these differed quantitatively from the effects in La2O2S:Eu they could be explained in terms of the analysis and the difference in location of the charge transfer peak and its shift with pressure.