  Samples for single-emitter spectroscopy are usually prepared by spin-coating
a dilute solution of emitters on a microscope cover slip of silicate based
glass (such as quartz). Here, we show that both borosilicate glass and quartz
contain intrinsic defect colour centres that fluoresce when excited at 532 nm.
In a microscope image the defect emission is indistinguishable from spin-coated
emitters. The emission spectrum is characterised by multiple peaks, most likely
due to coupling to a silica vibration with an energy of 160-180 meV. The
defects are single-photon emitters, do not blink, and have photoluminescence
lifetimes of a few nanoseconds. Photoluminescence from such defects may
previously have been misinterpreted as originating from single nanocrystal
quantum dots.
