Red to UV and blue up-conversion in alumina sol containing only Tm 3+ or both Tm 3+ and Yb 3+ ions via low energy pumping

This paper reports the up-conversion emission properties of alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions under 650 nm pumping using a low power xenon lamp source. Two UV emission bands which centered at 349 nm for the 1I6 → 3F4 transition of Tm3+ ion and at 367 nm for the 1D2 → 3H6 transition of Tm3+ ion and two blue emission bands which centered at 457 nm for the 1D2 → 3H4 transition of Tm3+ ion and at 485 nm for the 1G4 → 3H6 transition of Tm3+ ion have been observed. The up-conversion emission follows a two-photon absorption process for both blue bands, and the UV band centered at 367 nm but follows a cross-relaxation process for the UV band centered at 349 nm. The concentration quenching effect is relatively low in this material under 650 nm pumping. Due to the back energy transfer from Yb3+ to Tm3+ ions, the intensity of UV emission corresponding to the 1I6 → 3F4 transition of Tm3+ ion is stronger in alumina sol samples containing both Tm3+ and Yb3+ ions than in which containing only Tm3+ ions.