Calcination-assisted hydrothermal crystallization and comparative up-/down-conversion luminescence of RE3+ (RE=Ho, Er and Tm)-doped YbNbO4 and Yb3NbO7

The RE 3+ doped YbNbO 4 and Yb 3 NbO 7 nanophosphors (RE=Ho, Er and Tm) were synthesized via a calcination-assisted hydrothermal procedure. YbNbO 4 intensified almost the whole up-conversion (UC)/down-conversion (DC) emissions of RE 3+ by ∼2 times when compared with Yb 3 NbO 7 components, indicating that a lower symmetry environment in the former case is more favorable for photoluminescence. UC luminescence in each case was dominated by a green band at ∼539 nm for Ho 3+ and a NIR band at ∼803 nm for Tm 3+ , while doping YbNbO 4 and Yb 3 NbO 7 with Er 3+ separately yielded the slightly stronger green 556 nm and red 658 nm emissions. The UC/DC luminescence mechanisms were elaborated via Yb 3+ → RE 3+ forward/backward energy transfer and cross relaxation.