Broadband green upconversion luminescence of Ni2+ in KZnF3

The upconversion properties of divalent nickel doped into KZnF3 are reported. By exciting into the T-3(1g) (F-3) or E-1(g) excited state of Ni2+ with monochromatic light, a broad green luminescence around 20,000cm(-1) is observed that originates in the T-1(2g) higher excited state. The upconversion is shown to be a single ion process, consisting of a sequential two-photon absorption. The green luminescence is observed at all temperatures between 15 K and room temperature. This is strikingly different from what is observed in Ni2+ doped chloride and bromide materials in which the T-1(2g) --> (3)A(2g) luminescence is located in the red spectral range and is quenched well below room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.