A supersaturated glass-melt approach for growing micrometer-sized TGG single crystals

Abstract

Terbium gallium garnet (TGG, Tb3Ga5O12) is an important material used as Faraday rotator in telecommunication, in interferometric facilities and in other important technological and photonic applications. TGG can be synthesized using different methodologies, however obtaining single crystals on a large scale is still a challenge. In this paper, for the first time, micrometric cubic single crystals were obtained from rare earths supersaturated melted heavy metal oxide glass compositions. A systematic study of the glass composition allied to the control of cooling parameters allowed the synthesis of micro-scale single crystals. A chemical route is proposed to isolate the crystals from the parent glass without compromising their properties. A series of structural and spectroscopic techniques was employed to characterize the crystals, which crystallize in the Ia 3 ‾ d space group. XRD, Raman and EDS measurements demonstrate the formation of the Tb3Ga5O12 crystalline phase and the microscopy images show the presence of microcrystals with a perfect cubic shape and size between 50 and 100 μm. Luminescence analysis indicates a green emission between 530 and 560 nm characteristic of the 5D4 → 7F5 transitions of Tb3+ ions and the presence of Stark components as well resolved multiplets and perfectly coherent with the Stark components of the TGG crystal. Finally, SQUID measurements were performed on glass samples containing crystals and on isolated crystals after removal of the glass and both presented paramagnetic behavior. The effective magnetic moment obtained for the TGG microcrystals between 50 and 70 μm removed from the glass was 9.7 μB, the same value as the theoretical effective magnetic moment for Tb3+ ions. This achievement represents an advance in the methodologies for obtaining TGG cubes in the micro-scale range, opening the possibility of mass production of such crystal and its uses in different technological photonic applications.