  Irradiation of natural pink and brown diamond by middle-ultraviolet light
(photon energy > 4.1 eV) is seen to induce anomalous fluorescence phenomena at
N3 defect centres (structure N3-V). When diamonds primed in this fashion are
subsequently exposed to infrared light (even with a delay of many hours), a
transient burst of blue N3 fluorescence is observed. The dependence of this
IR-triggered fluorescence on pump wavelength and intensity suggest that this
fluorescence phenomena is intrinsically related to pink diamond photochromism.
An energy transfer process between N3 defects and other defect species can
account for both the UV-induced fluorescence intensity changes, and the
apparent optical upconversion of IR light. From this standpoint, we consider
the implications of this N3 fluorescence behaviour for the current
understanding of pink diamond photochromism kinetics.
