Controllable red, green and blue upconversion Luminescence of α-TeO 2:Tm 3+, Ho 3+, Yb 3+ nanoparticles

α-TeO 2:Ho 3+, Yb 3+, α-TeO 2:Tm 3+, Yb 3+ and α-TeO 2:Tm 3+, Ho 3+, Yb 3+ nanoparticles were prepared via a hydrothermal process. Under 980 nm excitation, α-TeO 2:Ho 3+, Yb 3+ nanoparticles showed green (545 nm) and red (651 nm) emission, which were attributed to the 5S 2→ 5I 8 and 5F 5→ 5I 8 transitions, respectively. The upconversion emission color changed markedly from yellow to green when the mole fraction of Yb 3+ ions changed from 5% to 15% due to the green emission at 545 nm increased. The α-TeO 2:Tm 3+, Yb 3+sample showed blue emission at 476 nm, which was attributed to the 1G 4→ 3H 6 transition, and two weak red (651, 675 nm) emissions, which were attributed to the 1G 4→ 3F 4 and 3F 2→ 3H 6 transitions, respectively. The relative intensity ratio of the blue emission to the red emissions increased gradually with increasing Yb 3+ concentration. Based on the generation of blue, green and red emissions, the α-TeO 2:Tm 3+, Ho 3+, Yb 3+ nanoparticles could compose different color, including white, by controlling the doping concentration of rare earths in the α-TeO 2 nanoparticles.