Designing thermally stimulated 1.06 mu m Nd3+ emission for the second bio-imaging window demonstrated by energy transfer from Bi3+ in La-, Gd-, Y-, and LuPO4

Lyu, T.; Dorenbos, P.

doi:10.1016/j.cej.2019.04.125

Designing thermally stimulated 1.06 mu m Nd3+ emission for the second bio-imaging window demonstrated by energy transfer from Bi3+ in La-, Gd-, Y-, and LuPO4

Title

Designing thermally stimulated 1.06 mu m Nd3+ emission for the second bio-imaging window demonstrated by energy transfer from Bi3+ in La-, Gd-, Y-, and LuPO4

Author

Lyu, T. (TU Delft RST/Luminescence Materials)
Dorenbos, P. (TU Delft RST/Luminescence Materials)

Date

2019

Abstract

We report a general methodology to the rational design of thermally stimulated short-wave infrared (SWIR) luminescence between ∼900 and 1700 nm by a new combination of using efficient energy transfer from Bi ³⁺ to Nd ³⁺ and an adjustable hole trap depth via valence band engineering. Predictions from a vacuum referred binding energy (VRBE) diagram are combined with the data from optical spectroscopy and thermoluminescence to show the design concept by using bismuth and lanthanide doped rare earth ortho-phosphates as model examples. Nd ³⁺ with its characteristic ⁴ F _3/2 → ⁴ I _j (j = 9/2, 11/2, 13/2) emission in the SWIR range is first selected as the emitting centre. The energy transfer (ET) processes from Bi ³⁺ or Tb ³⁺ recombination centres to Nd ³⁺ are then discussed. Photoluminescence results show that the energy transfer efficiency of Bi ³⁺ → Nd ³⁺ appears to be much higher than of Tb ³⁺ → Nd ³⁺ . To exploit this ET, thermally stimulated Bi ³⁺ A-band emission can then be designed by using Bi ³⁺ as a ∼2.7 eV deep electron trap in YPO ₄ . By combining Bi ³⁺ with Tb ³⁺ , Pr ³⁺ , or Bi ³⁺ itself, the holes trapped at Tb ⁴⁺ , Pr ⁴⁺ , or Bi ⁴⁺ will release earlier than the electrons captured at Bi ²⁺ . On recombination with Bi ²⁺ , Bi ³⁺ in its excited state is formed generating Bi ³⁺ A-band emission. Due to the ET of Bi ³⁺ → Nd ³⁺ 1.06 μm Nd ³⁺ emission appears in YPO ₄ . Herein, the thermally stimulated Nd ³⁺ SWIR emission is achieved by hole release rather than the more commonly reported electron release. The temperature when thermally stimulated Nd ³⁺ SWIR emission appears can further be engineered by changing the Tb ³⁺ or Pr ³⁺ hole trap depth in Y _1−x Lu _x PO ₄ by adjusting x. Such valence band engineering approach can also be applied to other compounds like La _1−x Gd _x PO ₄ and Gd _1−x La _x AlO ₃ solid solutions. Our work opens the avenue to motivate scientists to explore novel SWIR afterglow phosphors in a design way instead of by trial and error approach.