Preparation and upconversion luminescence of Er3 +/Yb3 + codoped Y2Ti2O7 nanocrystals

Abstract Er 3 + /Yb 3 + codoped pyrochlore-type (Y 0.99-x Er 0.01 Yb x ) 2 Ti 2 O 7 (x = 0, 2.5, 5.0, 7.5, 10.0 and 12.5 mol%) nanocrystals have been successfully prepared by the sol–gel process with citric acid as chelator. The samples annealed at 800 °C for 1 h exhibit good crystallinity and narrow size distribution with average size of 20–30 nm. Upon 980 nm excitation at room temperature, green (at ~ 525 and 545 nm) and red (at ~ 660 nm) upconversion emissions were observed, which are ascribed to the ( 2 H 11/2 , 4 S 3/2 ) →  4 I 15/2 and 4  F 9/2  →  4 I 15/2 transitions, respectively. And also, it has been found that the annealing temperatures and the Yb 3 + ion doping concentrations have greatly influenced on the upconversion luminescence intensity. The results show that Y 2 Ti 2 O 7 is an excellent host material for efficient upconversion nanophosphors.