Sources for this page
http://web.fccj.org/~ethall/thallium/thallium.htm
http://www.vcs.ethz.ch/chemglobe/ptoe/_/81t.html
http://www.andyhoppe.com/periodensystem/elemente/Thallium.htm
http://www.geocities.com/Area51/Shadowlands/4138/
Cotton, Albert F. and Geoffrey Wilkirson, Advanced Inorganic Chemistry: 4th edition,
John Wiley & Sons, Inc., New York, 1980, p.326-328.