Effect of Ho3+ and Tm3+ concentration on UV-VIS-NIR and upconversion luminescence in Ho:Tm:LiNbO3 crystals

Ho:Tm:LiNbO3 crystals with x mol% Ho3+ ions and y mol% Tm3+ ions (x - 0.1, 0.2, 0.25 and 0.3, y - 1, 2, 2.5 and 3) were grown by the Czochralski method. The influence of Ho3+ ions and Tm3+ ions concentration on the UV-VIS-NIR absorption spectra was discussed. The upconversion luminescence of Ho3+ and Tm3+ ions was observed under 800 nm excitation, and the energy transfer mechanisms of upconversion process were analyzed in details. The energy transfer mechanisms reflect that cross relaxation (CR), excited state absorption (ESA) and energy transfer (ET) from F-3(4) (Tm3+) to I-5(7) (Ho3+) are responsible for the upconversion emissions. The blue emission at around 473 nm, green emission at around 544 nm and red emission at around 648 nm were both enhanced obviously by doping 0.3mol% Ho3+ ions and 3mol% Tm3+ ions. The results show that Ho:Tm:LiNbO3 crystal is an excellent potential laser medium. (c) 2018 Elsevier B.V. All rights reserved.