Visible and infrared luminescence properties of Er 3+-doped Y 2Ti 2O 7 nanocrystals

Abstract

Er 3+-doped Y 2Ti 2O 7 nanocrystals were fabricated by the sol–gel method. While the annealing temperature exceeds 757 °C, amorphous pyrochlore phase Er x Y 2− x Ti 2O 7 transfers to well-crystallized nanocrystals, and the average crystal size increases from ∼70 to ∼180 nm under 800–1000 °C/1 h annealing. Er x Y 2− x Ti 2O 7 nanocrystals absorbing 980 nm photons can produce the upconversion (526, 547, and 660 nm; 2 H 11/2→ 4 I 15/2, 4 S 3/2→ 4 I 15/2, and 4 F 9/2→ 4 I 15/2, respectively) and Stokes (1528 nm; 4 I 13/2→ 4 I 15/2) photoluminescence (PL). The infrared PL decay curve is single-exponential for Er 3+ (5 mol%)-doped Y 2Ti 2O 7 nanocrystals but slightly nonexponential for Er 3+ (10 mol%)-doped Y 2Ti 2O 7 nanocrystals. For 5 and 10 mol% doping concentrations, the mechanism of up-converted green light is the two-photon excited-state absorption. Much stronger intensity of red light relative to green light was observed for the sample with 10 mol% dopant. This phenomenon can be attributed to the reduced distance between Er 3+–Er 3+ ions, resulting in the enhancement of the energy-transfer upconversion and cross-relaxation mechanisms.