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.