Selective Growth of Upconverting YbPO4:Ln (Ln = Er or Tm) Crystals in a Micro Reaction Cell

Highly crystalline upconversion fluorescence crystals of ytterbium phosphate (YbPO4) doped with Er3+ or Tm3+ were selectively and directly grown on a hydrophilic/hydrophobic self-assembled monolayer (SAM) template patterned by vacuum ultraviolet (VUV, lambda = 172 nm) light irradiation. First, a gelatin gel with an inner solution [(NH4)(2)HPO4] was selectively adsorbed on a hydrophilic surface, and the adsorbed gel was successfully used as the micro reaction cell between the inner solution and the outer solution [(CH3COO)(3)Yb center dot 4H(2)O]. The low crystalline YbPO4:Ln (Ln = Er or Tm) nanospheres, which are densely aggregated, were selectively and directly grown on the hydrophilic surface at 5 degrees C for 5 days. After annealing at 1100 degrees C for 10 h, their shape changed dramatically from an aggregation of nanospheres to an aggregation of well-formed nanocubes (200-600 nm). In addition, atoms and molecules of Yb, PO4, and Ln were highly and uniformly distributed in the YbPO4:Ln crystal. The YbPO4:Er and YbPO4:Tm crystals clearly show green and blue upconversion fluorescence, respectively, under 980 nm (near-infrared) laser irradiation.