florescence imaging explainedThis paper was written in 2002. TLT may have come from possible to probable. :)
https://download-v2.springer.com/static/pdf/716/art%253A10.1007%252Fs00330-002-1524-x.pdf?token2=exp=1431690715~acl=%2Fstatic%2Fpdf%2F716%2Fart%25253A10.1007%25252Fs00330-002-1524-x.pdf*~hmac=c06533c9ab90c96cd795038c35d3b96dd4a24f1671c7428cf1f0f40e4323b56c