Upconversion Photoluminescence Properties of KGd(WO₄)₂:Ho³⁺/Yb³⁺ Phosphors Synthesized by Microwave‐assisted Sol‐Gel Method

Abstract

Double tungstate KGd 1−x (WO 4 ) 2 :Ho 3+ /Yb 3+ phosphors with doping concentrations of Ho 3+ and Yb 3+ (x = Ho 3+ + Yb 3+ , Ho 3+ = 0.05, 0.1, 0.2, and Yb 3+ = 0.2, 0.45) were successfully synthesized by the microwave-assisted sol-gel method, and the upconversion (UC) mechanisms by a two-photon process have been investigated in detail. Well-crystallized particles, formed after heat-treatment at 900 C for 16 h, showed a fine and homogeneous morphology with particle sizes of 2-10 μm. Under excitation at 980 nm, the UC intensities of KGd 0.7 (WO 4 ) 2 :Ho 0.1 Yb 0.2 and KGd 0.5 (WO 4 ) 2 Ho 0.05 Yb 0.45 particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a strong 655-nm emission band in the red region, which were assigned to the 5 S 2 / 5 F 4 ! 5 I 8 and 5 F 5 ! 5 I 8 transitions, respectively. The Raman spectra of the particles indicated the appearance of strong peaks at higher frequencies (1050, 1106, 1250, and 1340 cm −1 ).