Order and disorder around Cr³⁺ in chromium doped persistent luminescent AB₂O₄ spinels

Abstract

X-ray absorption near edge structure (XANES) spectroscopy technique is used to better understand the charging and decharging processes of the persistent luminescence in the Cr 3+ doped AB 2 O 4 spinels (A = Zn, Mg and B = Ga and Al) with low photon energy excitation by visible light. Cr K edge XANES spectra have been simulated for different near neighbour environments around the Cr 3+ recombination centres and compared with the experimental curve. In Cr 3+ :ZnGa 2 O 4 compound, the Cr 3+ local structure corresponds mostly to that of a normal spinel (∼70%), while the rest comprises of distorted octahedral environment arising from cationic site inversion and a contribution from chromium clustering. This local structure is strongly different in Cr 3+ :MgGa 2 O 4 and Cr 3+ :ZnAl 2 O 4 where, for both cases, chromium clustering represents the main contribution. The strong correlation between the intensity of persistent luminescence and % of Cr in clusters leads us to infer that presence of Cr clusters is responsible for decrease of the intensity of the visible light induced persistent luminescence in the Cr 3+ doped AB 2 O 4 spinels.

Controlling disorder in the ZnGa2O4:Cr3+ persistent phosphor by Mg2+ substitution

“…The LCF fit to the XANES spectrum of ZMGO.Mg0.5 compound resulted in identical percentages to that of d-MGO spectrum, showing a steep decrease in ideal component contribution and an increase in Cr clusters contribution, and a corresponding decrease of NIRPL intensity. This result clearly substantiates our previous hypothesis that formation of Cr 3+ clusters leads to quenching of NIRPL 14. As previously reported, the lattice parameter increases from ZAO (zinc aluminate) to MGO to ZGO.…”

“…1.9Å and Cr 3+ with Cr as its first cationic neighbour (referred to as Cr clusters) spectrum with Cr-O distance ≈ 2Å. 14 The percentages of ideal, antisites and Cr clusters spectra contributions to the ZMGO spectra were calculated from the obtained d-ZGO and d-MGO combinations. The derived percentages for each compound are tabulated in Table 1.…”

“…Cr 3+ ions with Cr 3+ neighbours in Ga sites) to be detrimental for NIRPL induced by visible light excitation in these spinels. 14 16 To summarize, previous investigations not only pointed out to the major role of Cr 3+ neighbouring antisite defects in inducing visible light excited NIRPL in the above mentioned spinels, but also established the key role played by Cr clusters in the quenching of NIRPL emission intensity. In this paper, we have synthesized and characterized the solid solutions of Cr 3+ doped ZnGa 2 O 4 and MgGa 2 O 4 mixtures in different proportions, in order to control the amount of inversion defects and to validate our earlier finding that the presence of Cr cluster defects is detrimental to NIRPL emission.…”

Li5Zn8Ga5Ge9O36: Cr3+, Ti4+: A Long Persistent Phosphor Excited in a Wide Spectral Region from UV to Red Light for Reproducible Imaging through Biological Tissue

“…Figures 2b and 2c presentt he PLE and PL spectra of LZGG:1 .5 %C r 3 + ,0 .5 %T i 4 + ,w hich wereo btained by monitoringt he sample at different emission/excitation wavelengths.N oe xtra bands can be observed indicating that the Cr 3 + ions all have similar coordination configurations. [23] The PLE spectrum covers the entire UV-visible region, meaningr ed light activated PersL is expected. To investigate the PersL of the LZGG:1 .5 %C r 3 + ,0 .5 %T i 4 + LPP thoroughly,a PersLE spectrum (excited by a5 00 WX el amp, corrected) was captured.…”

Long term in vivo imaging with Cr3+ doped spinel nanoparticles exhibiting persistent luminescence

“…(iii) Defects responsible for this Cr-O bond variation in ZGO are likely to be Zn Ga and Ga Zn antisite defects. In addition, X-ray absorption near edge structure (XANES) spectroscopy technique was recently used [77] to better understand the charging and decharging processes of the persistent luminescence in the Cr doped spinels with visible light excitation. Cr K-edge XANES spectra have been simulated for different near neighbor environments around the Cr 3+ recombination centers and compared with the experimental spectrum.…”