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It is general knowledge in persistent luminescence that high-energy illumination, mostly ultraviolet light, is usually necessary in order to effectively charge persistent phosphors. However, the need for high-energy ultraviolet light excitation compromises some applications. In his pioneering work on ruby (Al 2 O 3 :Cr 3+ ) laser materials in 1960, Theodore Maiman observed an excited-state absorption phenomenon under the excitation of a high-intensity green-light flash tube. Inspired by Maiman's observation, here we propose a new two-photon up-conversion charging (UCC) concept to effectively charge Cr 3+ -activated near-infrared persistent phosphors using low-energy, high-intensity visible-light laser diodes. As an example, we demonstrate that a low-energy 635 nm laser diode can produce persistent luminescence in the LiGa 5 O 8 :Cr 3+ persistent phosphor at the same magnitude as that produced by high-energy 335 nm ultraviolet light from a xenon arc lamp. Moreover, the UCC appears to be a common phenomenon in persistent phosphors containing other UCC-enabling activators such as rare-earth Pr 3+ ions and transition metal Mn 2+ ions. The UCC technique offers a new way to study persistent luminescence and utilize persistent phosphors; for instance, in bioimaging it makes effective in vivo charging persistent optical probes using tissue-friendly visible light possible.
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Unlocking the key to persistent luminescence with X-ray absorption spectroscopy: a local structure investigation of Cr-substituted spinel-type phosphors
Developing new persistent luminescent phosphors, a unique class of inorganic materials that can produce a visible light emission lasting minutes to hours requires improving our understanding of their fundamental structure–property relationships. Research has shown that one of the most critical components governing persistent luminescence is the existence of lattice defects in a material. Specifically, vacancies and anti-site defects that coincide with substitution of the luminescent center, e.g. , Eu 2+ or Cr 3+ , are generally considered essential to generate the ultra-long luminescent lifetimes. This research solidifies the connection between defects and the remarkable optical properties. The persistent luminescent compound Zn(Ga 1−x Al x ) 2 O 4 ( x = 0–1), which adopts a spinel-type structure, is investigated by examining the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) at the Cr K and Zn K edges. This investigation reveals a structural distortion of the octahedrally coordinated main group metal site concurrent with increasing Al 3+ content. Moreover, these results suggest there is a dependence between the local crystallographic distortions, the presence of defects, and a material's persistent luminescence. In combination, this work provides an avenue to understand the connection between the structure–defect–property relationships that govern the properties of many functional inorganic materials.
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- Award ID(s):
- 1847701
- PAR ID:
- 10128726
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 21
- Issue:
- 35
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 19349 to 19358
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c9cp02655j
