Rubidium - ₃₇Rb: uses

The following uses for rubidium are gathered from a number of sources as well as from anecdotal comments. I would be delighted to receive corrections as well as additional referenced uses.

• rubidium is easily ionized, and so has possible use in "ion engines" for space vehicles (but caesium is somewhat more efficient)
• used as a "getter" in vacuum tubes
• photocell component
• used for making special glasses
• RbAg₄I₅ has the highest room temperature conductivity of any known ionic crystal. At ambient temperature, its conductivity is about the same as dilute sulphuric acid, suggesting uses in thin film batteries