Infrared to UV, VIS and NIR frequency upconversion luminescence studies of Tm3+-doped YbLiF4 crystal

A 4 mol% Tm3+-doped YbLiF4 crystal, grown by Czhochralski method, has been selected and the optical absorption spectrum has been recorded in parallel and perpendicular directions of c-axis in the spectral region of 850–1100 nm. The infrared to UV, VIS and NIR frequency upconversion luminescence properties of the 4 mol% Tm3+-doped YbLiF4 crystal have been investigated on exciting the sample with an intense 960 nm IR radiation of a semiconductor laser. The upconversion spectrum consists of strong emissions in the UV–VIS regions with peak positions at 290, 345, 360 and 450 nm along with relatively weak emissions in the VIS–NIR regions at 485, 648, 698 and 795 nm of the spectrum. The possible upconversion mechanisms have been discussed based on the phonon-assisted sequential two photon absorption and co-operative sensitization energy transfer processes. The temporal behavior of the upconversion emission profiles relating to various emitting levels have been measured and analysed.