Single crystal (0001) oriented, sapphire samples were implanted with 150 keV Cr ions at fluences between 6.0×1014 and 4.0×1015 Cr/cm2. The peak concentrations ranged from 0.04 to 0.28 at %. Characteristic photoluminescence of the R lines at 694.3 and 692.9 nm was observed. Annealing at 1450 °C for 2 h increased the luminescence intensity by a factor of 45, due to the increasing fraction of substitutional Cr ions as confirmed by Rutherford backscattering spectrometry. The Cr luminescence decay rate in an annealed sample implanted with 3.0×1015 at/cm2 at 300 K is 299 s–1. Decay rates were also measured for samples covered with a range of transparent liquids (refractive index n = 1.33–1.57), showing a clear increase with increasing refractive index of the liquid. This effect is explained by the increase of the local optical density of states in the Cr-implanted region. By comparing the measured data with the calculated optical density of states the radiative decay rate is found to be 164±10 s–1 and the internal quantum efficiency ~50%. The quantum efficiency decreases slightly for ncreasing Cr concentration.

J. Appl. Phys.
Photonic Materials

Hensen, T.M, de Dood, M.J.A, & Polman, A. (2000). Luminescence quantum efficiency and local optical density of states in thin film ruby made by ion implantation. J. Appl. Phys., 88, 5142–5147.