Visible quantum cutting through downconversion in KLiGdF_5:Eu~(3+) crystals

摘要

Visible quantum cutting through downconversion is observed for the Gd~(3+)-Eu~(3+) couple in KLiGdF_5:Eu~(3+) (KLGF:Eu~(3+)). In this Gd~(3+)-based fluoride, visible quantum cutting, the emission of two photons of visible light per absorbed photon, occurs upon vacuum ultraviolet excitation of Gd~(3+) at the ~6G_J level via two-step energy transfer from Gd~(3+) to Eu~(3+) by cross relaxation and sequential transfer of the remaining excitation energy. The dependence of the efficiency of cross relaxation required for visible quantum cutting on the Eu~(3+) doping concentration is discussed in terms of the probability of energy transfer and the behavior of decay of the ~5D_0 emission of Eu~(3+), and it is found that the KLGF crystal doped with 2 at. % Eu~(3+) exhibits the maximum cross-relaxation efficiency of 0.4. From the number of nearest neighbors around Gd~(3+) ions and the ~5D_0 emission intensity, energy transfer from excited Gd~(3+) ions is determined to extend to the fourth-nearest Eu~(3+) neighbors in the quantum cutting process.