Pump power induced tunable upconversion emissions from Er3+/Tm3+/Yb3+ ions tri-doped SrY2O4 nanocrystalline phosphors
Abstract
RE3+ (Er3+/Tm3+/Yb3+) ions tri-doped SrY2O4 nanocrystalline phosphors were synthesized by a citrate sol–gel method. After annealing at 1300 °C, the structure was identified to be pure orthorhombic and the particles were found to be nearly spherical in shape. The up-conversion emission spectra of the SrY2O4:1Er3+ phosphor revealed a bright green emission (4S3/2 → 4I15/2) around 551 nm. To enhance the red emission of the Er3+ ions, Yb3+ ions were co-doped with Er3+ ions, leading to a greenish yellow emission under 980 nm excitation. In the case of the 1Er3+/1Tm3+/3Yb3+ ions tri-doped phosphor, white-light emission was observed corresponding to the 1G4 → 3H6 (Tm3+), 4S3/2 → 4I15/2 (Er3+) and 4F9/2 → 4I15/2 (Er3+) transitions at 487, 551 and 664 nm, respectively. It was interestingly noticed that, when the exciting pump power was changed from 100 to 900 mW, the blue emission band of the Tm3+ ions was enhanced by the suppression of the red and green emission bands of the Er3+ ions so that the chromaticity coordinates were also moved to the cyan emission region. This feature suggests that the Er3+ ion may also act as a sensitizer for the Tm3+ and Yb3+ ions and a possible energy transfer mechanism was also discussed.
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