Microstructure Control and Upconversion Emission Improvement of Y 2 O 3 :Ho 3+ /Yb 3+ Particles Prepared by Spray Pyrolysis

Upconversion (UC) properties of Y2O3:Ho3+/Yb3+ spherical particles synthesized by spray pyrolysis were investigated by changing the dopant concentration and calcination temperature. Citric acid (CA), ethylene glycol (EG) and N, N-dimethylformamide (DMF) were used to control the microstructure of Y2O3:Ho3+/Yb3+ particles. In terms of achieving the highest UC green emission intensity, the optimal concentrations of Ho3+ and Yb3+ were found to be 0.3% and 3.0%, respectively. In addition, the UC intensity of Y2O3:Ho3+/Yb3+ showed a linear relationship with the crystallite size. The use of organic additives allows Y2O3:Ho3+/Yb3+ particles to have a spherical and dense structure, resulting in significantly reducing the surface area while maintaining high crystallinity. As a result, the UC emission intensity of Y2O3:Ho3+/Yb3+ particles having a dense structure showed the UC emission intensity about 3.8 times higher than that of hollow particles prepared without organic additives. From those results, when Y2O3:Ho3+/Yb3+ particles are prepared by the spray pyrolysis process, the use of the CA/EG/DMF mixtures as organic additives has been suggested as an effective way to substantially increase the UC emission intensity.