Oliver S. Wenger and Hans U. Güdel
Influence of Crystal Field Parameters on Near-Infrared to Visible Photon Upconversion in
Ti 2+ and Ni 2+ Doped Halide Lattices
Structure and Bonding 106, 59-70 (2004)
Abstract:
The near-infrared to visible photon upconversion properties
of Ti2+ and Ni2+ doped chloride and bromide lattices are
summarized and discussed. They are used to illustrate the young and emerging
field of transition metal based upconversion systems. It is demonstrated that
transition metal upconversion properties can be tuned by chemical and structural
variation. The change from NaCl to MgCl2 as a host for
Ti2+ induces a crossover in the intermediate metastable excited state
of Ti2+ from 3T2g to
1T2g, leading to an order of magnitude enhancement of the
15 K near-infrared to visible upconversion efficiency. The change from
CsCdCl3 to MgBr2 as host lattices for Ni2+
dopant ions induces a crossover in the upper emitting excited state of
Ni2+ from 1T2g to 1A1g,
manifesting itself in a change from broad-band to sharp-line visible
upconversion luminescence. These results are rationalized on the basis of
varying covalency and crystal field strength.