Control of infrared cross-relaxation in LiNbO 3 :Tm 3+ through high-pressure

The cross-relaxation process between the lower excited states of thulium ions has a strong influence on its main infrared emissions, but also in the population of higher excited states that lead to characteristic blue upconversion. This work investigates this process in LiNbO3:Tm3+ by means of time-resolved spectroscopy at high pressure. It is demonstrated that through the application of high-pressure it is possible to enhance its probability and to investigate its influence on the photoluminescence spectra and corresponding lifetimes of Tm3+. The results are analyzed in terms of the effect of high pressure on parameters such as Tm3+-Tm3+ distance through the equation-of-state of LiNbO3, refractive index or Tm3+-Tm3+ energy transfer characteristics (absorption/emission overlap integral), to conclude that the major multipole interaction responsible for cross-relaxation is the quadrupole-quadrupole interaction. This conclusion supports and clarifies previous dynamical models for energy transfer on the basis of spectroscopic studies carried out in LiNbO3:Tm3+ as a function of Tm3+ concentration. (C) 2015 Optical Society of America