Designing thermally stimulated 1.06 µm Nd 3+ emission for the second bio-imaging window demonstrated by energy transfer from Bi 3+ in La-, Gd-, Y-, and LuPO 4

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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 3/24 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.

Original languageEnglish
Pages (from-to)978-991
JournalChemical Engineering Journal
Volume372
DOIs
Publication statusPublished - 2019

Keywords

  • Afterglow
  • Bismuth
  • Energy transfer
  • Hole release
  • Valence band engineering

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