Analysis of Excitation Energy Transfer in LaPO 4 Nanophosphors Co-Doped with Eu 3+ /Nd 3+ and Eu 3+ /Nd 3+ /Yb 3+ Ions.

Nanophosphors are widely used, especially in biological applications in the first and second biological windows. Currently, nanophosphors doped with lanthanide ions (Ln 3+ ) are attracting much attention. However, doping the matrix with lanthanide ions is associated with a narrow luminescence bandwidth. This paper describes the structural and luminescence properties of co-doped LaPO 4 nanophosphors, fabricated by the co-precipitation method. X-ray structural analysis, scanning electron microscope measurements with EDS analysis, and luminescence measurements (excitation 395 nm) of LaPO 4 :Eu 3+ /Nd 3+ and LaPO 4 :Eu 3+ /Nd 3+ /Yb 3+ nanophosphors were made and energy transfer between rare-earth ions was investigated. Tests performed confirmed the crystal structure of the produced phosphors and deposition of rare-earth ions in the structure of LaPO 4 nanocrystals. In the range of the first biological window (650-950 nm), strong luminescence bands at the wavelengths of 687 nm and 698 nm ( 5 D 0 → 7 F 4 :Eu 3+ ) and 867 nm, 873 nm, 889 nm, 896 nm, and 907 nm ( 4 F 3/2 → 4 I 9/2 :Nd 3+ ) were observed. At 980 nm, 991 nm, 1033 nm ( 2 F 5/2 → 2 F 7/2 :Yb 3+ ) and 1048 nm, 1060 nm, 1073 nm, and 1080 nm ( 4 F 3/2 → 4 I 9/2 :Nd 3+ ), strong bands of luminescence were visible in the 950 nm-1100 nm range, demonstrating that energy transfer took place.