Enhanced cooperative absorption and upconversion in Yb3+doped YAG nanophosphors

Enhanced cooperative absorption and upconversion emission of Yb3+ pairs in nanocrystalline YAG is observed. The nanocrystallites synthesized by a modified sol-gel method have an average size of 96 nm. The estimated concentration normalized ratio of maximum visible absorption to maximum IR absorption emission of 7.55 × 10−22 cm3 is about four orders of magnitude higher than the highest reported value to date, and more than seven orders higher than for bulk monocrystalline YAG:Yb3+. Strong cooperative upconversion emission is observed under IR pump at 940 nm.