Visible quantum cutting in Eu3+-doped gadolinium fluorides via downconversion

Emission of two photons of visible light per absorbed vacuum ultraviolet photon (known as quantum cutting) is reported for LiGdF4 : Eu3+ and GdF3 : Eu3+. For every Gd3+ ion excited in the (6)G(J) levels (around 50 000 cm(-1)) or higher, two visible photons can be emitted due to D-5(J) --> F-7(J) transitions on two Eu3+ ions. The first Eu3+ ion is excited into the D-5(0) level by cross relaxation of the energy corresponding to the (6)G(J) --> P-6(J) transition on Gd3+. The second Eu3+ ion is excited by direct energy transfer of the remaining energy from Gd3+ (P-6(J)) to Eu3+. It is shown that this two-step energy transfer process is very efficient at room temperature. Since this process is the opposite of the well-known upconversion process, we call it downconversion. (C) 1999 Elsevier Science B.V. All rights reserved.