Absorption and luminescence spectroscopy of Zn2SiO4 willemite crystals doped with Co2+

The polarized absorption spectra of Zn2SiO4 willemite crystals doped with Co2+ consist of three band systems in the near-infrared and visible spectra region centered at 3800, 7000, and 17000 cm−1, respectively. In the tetrahedral approximation they are assigned to the d → d transitions 4A2 → 4T2, 4T1(4F), and 4T1(4P), respectively. The crystal field parameter 10Dq is 4000 cm−1, and the Racah parameters B and C are 740 and 3330 cm−1, respectively. From the fine structure in the origin region of the 4A2 → 4T2 absorption band it follows that the 4A2 ground-state splittings of Co2+ occupying the two crystallographically inequivalent Zn2+ sites of C1 symmetry are 13 and 15 cm−1, respectively. Only a weak emission originating at 15335 cm−1 is observed upon 4A2 → 4T1(4P) photoexcitation. It is assigned to the 2E → 4A2 sharp-line luminescence of Co2+ located in a minority site. No luminescence is observed from regularly incorporated Co2+ ions.