Delayed luminescence and thermoluminescence in laboratory-grown diamonds

TL;DR

This study investigates the mechanisms behind different luminescence bands in lab-grown diamonds, proposing a charge trapping model for orange phosphorescence and identifying defect-related origins for red phosphorescence.

Contribution

It introduces an alternative charge trapping model for long-lived phosphorescence and clarifies the origins of orange and red luminescence in diamonds.

Findings

Charge trapping explains orange phosphorescence

Red phosphorescence linked to point defects

Luminescence depends on excitation and temperature

Abstract

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.