Ho3+/Yb3+/Tm3+ tri-doped NaY1-x(WO4)2 phosphors with proper doping concentrations of Ho3+, Yb3+ and Tm3+ (x = Ho3+ +Yb3+ +Tm3+, Ho3+ = 0.04, 0.03, 0.02, 0.01, Yb3+ = 0.35, 0.40, 0.45, 0.50 and Tm3+ = 0.01, 0.02, 0.03, 0.04) were successfully synthesized via the microwave sol-gel route, and their upconversion properties were investigated. Well-crystallized microcrystalline particles showed fine and homogeneous microcrystalline morphology with particle sizes of 1-2 μm. The optical properties were comparatively examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the doped particles exhibited white emissions based on blue, green and red emission bands, which correspond to the 1G4→ 3H6 transitions of Tm3+ in the blue region, the 5S2/ 5F4→ 5I8 transitions of Ho3+ in the green region, the 5F5→ 5I8 transitions of Ho3+, and the 1G4→ 3F4 and 3H4→ 3H6 transitions of Tm3+ in the red region. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

• Chang Sung Lim(Department of Advanced Materials Science & Engineering, Hanseo University) Corresponding author