Concentration‐Induced Hetero‐Valent Partial‐Inverse Occupation of Infrared Phosphor

Abstract

Infrared luminescent materials have evoked much attention from chemists and material scientists. Although substantial progress is made in materials design, the luminescent mechanism remains ambiguous in the complex structures, presenting major barriers to developing novel infrared luminescent materials. Herein, this study aims to deliberate a complete discussion on infrared phosphors with concentration-induced hetero-valent partial-inverse occupation. High-resolution synchrotron X-ray diffraction and Raman spectroscopy reveal the subtle structural change in LiGa 5(1−x) O 8 :5xCr 3+ . Besides, Cr K-edge wavelet analysis and extended X-ray absorption fine structure illustrate the impact of Cr in the second shell of another Cr ion and the practical coordination of Ga and Cr ions. Furthermore, unexpected two-center Cr 3+ emissions and the Cr-Cr pair emission are observed at high Cr concentrations. Variation between the zero-phonon line and N-line at different temperatures is demonstrated. Finally, the structural and luminescent properties are comprehensively discussed, providing the origin of the unexpected Cr2 emission. This study not only provides insight into the hetero-valent partial-inverse occupation process in inorganic materials but also sheds light on developing novel infrared luminescent materials.

Sharp-to-Broad Band Energy Transfer in Lithium Aluminate and Gallate Phosphors for SWIR LED

“…The Cr K -edge and Ni K -edge X-ray absorption near-edge structure (XANES), which utilize synchrotron radiation, stand as formidable tools in the investigation of charge variations in materials research. As illustrated in Figure a, the Cr K -edge XANES spectra closely resemble the Cr 3+ standard across all samples, confirming the ionic charge of chromium . Notably, the inset in the figure highlights a shift in the absorption peaks of Cr toward higher energy levels, approximately 1 eV.…”

“…As illustrated in Figure 2a, the Cr K-edge XANES spectra closely resemble the Cr 3+ standard across all samples, confirming the ionic charge of chromium. 27 Notably, the inset in the figure highlights a shift in the absorption peaks of Cr toward higher energy levels, approximately 1 eV. The increase in the Al concentration within the structure triggers a change in the oxidation states of Cr due to structural contraction, resulting in a stronger ionic Cr−O bonding.…”

Hidden Hexavalent Chromium Ions with Subtle Structural Evolution in Near-Infrared Phosphors

“…Previous studies have investigated several Cr 3+ -doped NIR phosphors, such as La 3 Ga 5 GeO 14 :Cr 3+ (garnet-type), ZnGa 2 O 4 :Cr 3+ (spinel-type), Mg 2 InSbO 6 :Cr 3+ (perovskite-type), and Sr 9 Sc­(PO 4 ) 7 (whitlockite-type). − These materials exhibit promising luminescent properties and have been extensively studied for their potential applications in different technological fields. − In all NIR phosphor structures, six-coordination sites within a crystal lattice play a crucial role in modulating its luminescent properties. When Cr 3+ ions occupy six-coordination sites, such as octahedral or distorted octahedral environments, it affects the crystal field splitting and energy levels of the electronic orbitals. − …”