Upconversion in a divalent rare earth ion: optical absorption and luminescence spectroscopy of Tm2+ doped SrCl2

Abstract Crystals of 2% Tm 2+ doped SrCl 2 were studied by variable temperature optical absorption and luminescence spectroscopy. The absorption spectrum consists of the weak 4f 13 intraconfigurational 2 F 7/2 → 2 F 5/2 transition around 8840 cm −1 and a series of intense parity allowed f→d transitions above 15,000 cm −1 . Luminescence is observed from the 4f 13 2 F 5/2 excited state as well as from the lowest-energetic 4f 12 5d excited state at all temperatures between 10 and 300 K . Upconversion luminescence from the latter is observed after cw- (lamp) excitation at 8840 cm −1 into 2 F 5/2 at 15 K , as well as after pulsed (laser) excitation at 1064 nm at 300 K .