Energy transfer processes on both Er3+ ion concentration and excitation densities in Yb3+–Er3+ codoped LaF3 matrix

The effects of both Er3+ ion concentration and excited density upon frequency upconversion fluorescence emissions in Er3+/Yb3+-codoped LaF3 powder are investigated. The results reveal that a higher Er3+ concentration can induce not only upconversion emission enhancements but also the changes among the relative intensities of the 407, 519, 539 and 651 nm radiation transitions as the samples are excited within the ranges of 20 to 700 mW with 978 nm laser diode (LD) as an excitation source. The changes are described by a schematic level model with the cross-relaxation processes between Er3+ ions and a series of dynamic equations that take into account the population of temperature dependent in Er3+.