Color-Tunable Upconversion in Er³⁺/Yb³⁺-Codoped KLaF₄ Nanophosphors by Incorporation of Tm³⁺ Ions for Biological Applications.

ABSTRACT: Heavily doped nanocrystals of host KLaF₄ with rare earth (RE³⁺ = Er³⁺, Tm³⁺, and Yb³⁺) ions prepared by a simple one-step template-free wet-chemical route have been reported. Prepared KLaF₄ nanocrystals reveal phase-pure cubic structures (lattice constant a = 5.931Å) with space group Fm3m. Precisely defined molar ratios of heavily dopant RE³⁺ ions allow us to achieve wide color upconversion (UC) emission tunability (blue, green to yellow-orange-red) and white light, without any morphology and structure changes. The enhanced red emission by a factor of ?120 has been achieved in 20% Yb³⁺ and 5% Tm³⁺ ions in KLaF₄:1% Er³⁺ nanocrystals, which is due to an efficient sensitizer-acceptor (Yb³⁺ to Er³⁺ and Tm³⁺ ions) energy transfer and interexchange energy process between acceptors. For the first time, the key role of sensitizer (Yb³⁺) for UC emission energy transfer to Er³⁺ and/or Tm³⁺ is experimentally demonstrated. The evidence of upconversion photoluminescence excitation spectra reveals a broad safe biological excitation window (690-1040 nm), which can be well demonstrated by low-cost NIR diode lasers/LEDs. The applicability of these cubic nanophosphors is demonstrated as light-emitting polymer composite coatings and blocks for LEDs and solar cell panels. These well-dispersed UC nanocrystals can also be found to have greater use in bioimaging and spectral studies.

SUBMITTER: Gupta M 

PROVIDER: S-EPMC6648747 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature