Thermometry and up-conversion luminescence of Yb(3+)-Er(3+) co-doped Na2Ln2Ti3O10 (Ln = Gd, La) phosphors.

Yb(3+)/Er(3+)-ion co-doped Na2Ln2Ti3O10 (Ln = Gd, La) up-conversion (UC) phosphors were successfully synthesized by a sol-gel method, and their crystal structures were characterized by powder X-ray diffraction. Dazzling yellow-greenish light was emitted under the excitation of 980 nm near-infrared (NIR) light, composing green and red emission bands from the (2)H11/2/(4)S3/2→(4)I15/2 and (4)F9/2→(4)I15/2 transitions of Er(3+), respectively. The optimal composition and synthesis parameters were determined according to their UC emission intensity. The photon absorption and emission processes were illustrated based on the UC mechanism, in which energy transfer (ET) from Yb(3+) to Er(3+) plays a pivotal role and has been proved by the variation of green emission lifetime in Er(3+) singly and Yb(3+)/Er(3+) co-doped Na2Ln2Ti3O10 samples. The temperature-dependent fluorescence intensity ratios (FIR) of the two thermal coupled energy level (TCL) emission from (2)H11/2→(4)I15/2 (526 nm) and (4)S3/2→(4)I15/2 (549 nm) were calculated in the range of 290-490 K, and their sensitivity values were approximately 0.0058 K(-1) for Na2Gd2Ti3O10 at 490 K and 0.0061 K(-1) for Na2La2Ti3O10 at 470 K, as potential optical temperature sensor.