  The blue-green phosphorescence/thermoluminescence is most commonly observed
in diamonds following excitation at or above the indirect band gap and has been
explained by a substitutional nitrogen-boron donor-acceptor pair recombination
model. Orange and red phosphorescence have also been frequently observed in
lab-grown near-colourless high-pressure high-temperature diamonds following
optical excitation, and their luminescence mechanisms are shown to be different
from that of the blue-green phosphorescence. The physics of the orange and red
luminescence and phosphorescence bands including the optical-excitation
dependency (UV-NIR), temperature dependency (20 - 573 K), and related charge
transfer process are investigated by a combination of self-built time-resolved
imaging/spectroscopic techniques. In this paper, an alternative model for
long-lived phosphorescence based on charge trapping is proposed to explain the
orange phosphorescence/ thermoluminescence band. Additionally, the red
phosphorescence band are attributed to point defect which possibly has a
three-level phosphorescence system.
