Visible quantum cutting through downconversion in KLiGdF5:Eu3+ crystals

Visible quantum cutting through downconversion is observed for the Gd3+–Eu3+ couple in KLiGdF5:Eu3+ (KLGF:Eu3+). In this Gd3+-based fluoride, visible quantum cutting, the emission of two photons of visible light per absorbed photon, occurs upon vacuum ultraviolet excitation of Gd3+ at the GJ6 level via two-step energy transfer from Gd3+ to Eu3+ 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 Eu3+ doping concentration is discussed in terms of the probability of energy transfer and the behavior of decay of the D05 emission of Eu3+, and it is found that the KLGF crystal doped with 2at.% Eu3+ exhibits the maximum cross-relaxation efficiency of 0.4. From the number of nearest neighbors around Gd3+ ions and the D05 emission intensity, energy transfer from excited Gd3+ ions is determined to extend to the fourth-nearest Eu3+ neighbors in the quantum cutting process.