Intense Blue Chromophores in Cobalt Doped Phenacite‐Type Zinc Germanate System through Jahn‐Teller Distortion of Co Tetrahedron

Abstract

AbstractIn the quest for new blue chromophores with less usage of cobalt alternatives to the carcinogenic and expensive zinc‐cobalt aluminate system, we developed cobalt doped phenacite type zinc germanate system. Rietveld analysis reveals that the CoO4 tetrahedron intensely experienced Jahn‐Teller distortions leading to irregular geometry on substitution. The UV‐vis‐IR absorption spectra exhibit intense Co2+ d‐d transitions with three fold splitting associated with the CoO4 tetrahedron in the visible and IR region, indicating low symmetry. The crystal field strength 10Dq, Racah parameter and Nephelauxetic ratio variations reflect on the improved covalency of the Co2+ environment. Thus the synergetic effect of Jahn‐Teller distortions and covalency of the CoO4 tetrahedron lead to strong absorptions in the green to red region resulting in intense blue colors with low cobalt content (2.2 to 8.9 mol %). The typical composition Zn1.6Co0.4GeO4 exhibits intense blue hue b*=−58.64, much higher than that of the commercial CoAl2O4 system.