Upconversion Luminescence in Er ³⁺ Doped and Yb ³⁺ /Er ³⁺ Codoped Yttria Nanocrystalline Powders

Y 1.9 Er 0.1 O 3 and Y 1.7 Yb 0.2 Er 0.1 O 3 nanocrystalline powders were prepared via a reverse‐strike coprecipitation method using nitrates and ammonia as raw materials. The obtained powders were of cubic‐phase structure of Y 2 O 3 and the particle size was in the range of ∼60–80 nm. Strong red ( 4 F 9/2 – 4 I 15/2 ) and green ( 2 H 11/2 / 4 S 3/2 – 4 I 15/2 ) upconversion luminescence were observed in all the samples when excited with a 980‐nm continuous wave diode laser. The possible upconversion mechanisms in Y 1.9 Er 0.1 O 3 and Y 1.7 Yb 0.2 Er 0.1 O 3 were discussed. Power studies indicated that two‐photon processes are responsible for the green and red upconversion luminescence in these systems. The codoping of Yb 3+ greatly enhanced the red ( 4 F 9/2 – 4 I 15/2 ) upconversion emission.