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Environmental applications of luminescence

Effect of ytterbium ions on broadband anti-stokes visible emission

Robert T. M. C. W. Strek1

1Institute of Low Temperature and Structure Research PAS, Poland

E-mail: r.tomala@intibs.pl

The Laser Induced White Emission (LIWE) phenomena has received much attention in recent years, however, the mechanism behind this process is still not entirely understood. LIWE of Y2(1-x)Yb2xSiO7 nanocrystallites was observed upon excitation with CW infrared laser diode. The visible broad emission centered at 600-700 nm was dependent on concentration of Yb3+ and it increased exponentially with excitation power density. It was detected blue shift of the LIWE emission with increase in Yb3+ concentrations. Increase in the Yb3+ concentrations leads to rise in the LIWE absolute intensity. It was shown that the N order parameters of LIWE process increase from 3 to 7 with increase of Yb3+ concentration from 1 at.% to 5 at.% while the further increase leads to saturation and reach a magnitude 8 for fully concentrated nanocrystals. The laser induced photocurrent assisting generation of visible broad band emission was measured. It increased exponentially with applied excitation power and concentration of Yb3+ ions. The increase in the concentration of Yb3+ ions to 5 at.% leads to small increase in the photocurrent, while the further increase lead to significantly rise in the photocurrent. The avalanche ionization process in Yb2+/Yb3+ mixed valence pair was proposed as a tentative model of LIWE phenomenon. The ionization process occurs due to the cooperative energy transfer from several Yb3+ ions to Yb2+/Yb3+ mixed valence pair followed by the ejection of electron.

Keywords: white light source, nanocrystals,

Acknowledgments: The authors would like to thank the National Science Centre, Poland for financial support (grant no. 2020/37/B/ST5/02399).

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