Bismuth germanate

Most commonly the term refers to the compound with chemical formula Bi4Ge3O12 (BGO), with the cubic evlitine crystal structure, used as a scintillator.

[4] This bismuth germanate has high electro-optic coefficients (3.3 pm/V for Bi12GeO20),[5] making it useful in nonlinear optics for building Pockels cells, and can also be used for photorefractive devices for ultraviolet range.

[8] The crystals of BGO and similar compounds BSO (Bi12SiO20, bismuth silicon oxide, sillenite) and BTO (Bi12TiO20), are photorefractive and photoconductive.

They can be used in electro-optical applications, like optical PROM, PRIZ spatial light modulators, realtime hologram recording, correlators, and systems for adaptive correction of ultrashort laser pulses, and in fiber optic sensors for electric and magnetic fields.

Thin film sillenite structures, which can be deposited e.g. by sputtering, have wide range of potential applications.

When sputtering, the target has to be kept below 450 °C as otherwise the bismuth vapor pressure would get the composition out of stoichiometry, but above 400 °C to form the piezoelectric γ phase.

BGO scintillator crystals covered with a (partly dilapidated) white paint mask
A crystal cylinder rests on a piece of white cloth, which itself sits on a blue surface of a table.
1-inch diameter, 1-inch tall crystal of BGO. BGO degenerates under UV light, so here it is illuminated with an LCD laptop screen to ensure minimal UV exposure.