Abstracts

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 Y_2(1-x)Yb_2xSiO₇ 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.