Enhanced upconversion luminescence of GdVO₄:Er³⁺/Yb³⁺ prepared by spray pyrolysis using organic additives

Spray pyrolysis was applied to prepare Er³⁺/Yb³⁺-doped GdVO₄ particles, and their emission properties were investigated by varying the Er³⁺/Yb³⁺ content and the calcination temperature from 900 to 1400 °C. Ethylene glycol (EG), citric acid (CA) and N,N-dimethylformamide (DMF) were used as organic additives in order to improve the upconversion of GdVO₄:Er³⁺/Yb³⁺. The resulting GdVO₄:Er³⁺/Yb³⁺ particles show strong green emission due to ²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ and weak red peak due to the ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺. From the result observed by changing the pumping power of the near-infrared (NIR, 980 nm) laser, the observed green emission is caused by a typical two-photon process. In terms of achieving the highest upconversion luminescence, the optimal Er³⁺ and Yb³⁺ contents are 1.5% and 20% with respect to Gd, respectively. The luminescence intensity steadily increased as the calcination temperature was elevated up to 1200 °C due to the increment of crystallinity. The upconversion intensity showed a linear relationship with the crystallite size in all the calcination temperature range. Using the EG/CA/DMF mixture as organic additives improves the upconversion emission about 4.3 times higher than when no organic additives are used, due to the enhancement of crystallinity as well as the enlargement of primary particle size.