Blue, green, yellow and red upconversion fluorescence in Tm3+/Ho3+: Cs2NaGdCl6 crystals under 785 nm laser excitation

1% Tm3+, 10% Ho3+ single-doped and 10% Tm3+, 10% Ho3+ co-doped Cs2NaGdCl6 samples were synthesized by Morss method E. Under 785 nm semiconductor laser pumping, the upconversion fluorescence in Tm3+ single-doped and Tm3+, Ho3+ co-doped Cs2NaGdCl6 was investigated at room temperature. For 1% Tm3+-doped sample, three upconversion emission bands near 483 nm, 658 nm and 701 nm were obtained and assigned to be (1)G(4) -> H-3(6), (1)G(4) -> F-3(4) and F-3(3) -> H-3(6), respectively. For 10% Tm3+, 10% Ho3+ co-doped sample, four strong upconverted emissions near 492 nm. (blue), 543 nm (green), 588 nm (yellow) and 657 nm (red) were measured and assigned to be F-5(3) -> I-5(8), S-5(2) -> I-5(8), (5)G(4) -> I-5(6) and F-5(5) -> I-5(8) transitions of Ho3+ ions. With the help of the measuring power dependence of all these upconversion emissions, a reasonable upconversion mechanism model responsible for them was presented. The analysis of these upconversion emissions confirmed the efficient energy transfer from Tm3+(F-3(4)) to Ho3+(I-5(7)) ions. (C) 2007 Elsevier B.V. All rights reserved.