Visible quantum cutting via downconversion in LiGdF4 : Er3+, Tb3+ upon Er3+ 4f11 → 4f105d excitation

Visible quantum cutting (the emission of two photons of visible light per absorbed photon) is reported for LiGdF4 codoped with Er3+ and Tb3+. In this compound visible quantum cutting is achieved through downconversion, i.e., by making use of energy transfer between different lanthanide ions. Upon VUV excitation in the 4f(10)5d levels of Er3+, part of the excitation energy can be transferred to Gd3+ by cross-relaxation, yielding both Er3+ and Gd3+ in an excited state. This is followed by the emission of two visible photons: one from Er3+ due to the S-4(3/2) --> I-4(15/2) transition, and, after energy transfer from Gd3+ to Tb3+, one from Tb3+ due to the D-5(J) --> F-7(J) transition. It is shown that this process occurs, next to other energy transfer processes from the Er3+ 4f(105)d states to Gd3+ yielding only one visible photon. (C) 2000 Elsevier Science B.V. All rights reserved.