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Photoluminescence of monovalent indium centres in phosphate glass

View Article: PubMed Central

ABSTRACT

Valence control of polyvalent cations is important for functionalization of various kinds of materials. Indium oxides have been used in various applications, such as indium tin oxide in transparent electrical conduction films. However, although metastable In+ (5 s2 configuration) species exhibit photoluminescence (PL), they have attracted little attention. Valence control of In+ cations in these materials will be important for further functionalization. Here, we describe In+ species using PL and X-ray absorption fine structure (XAFS) analysis. Three absorption bands in the UV region are attributed to the In+ centre: two weak forbidden bands (1S0 → 3P1,1S0 → 3P2) and a strong allowed band (1S0 → 1P1). The strongest PL excitation band cannot be attributed to the conventional allowed transition to the singlet excited state. Emission decay of the order of microseconds suggests that radiative relaxation occurs from the triplet excitation state. The XAFS analysis suggests that these In+ species have shorter In–O distances with lower coordination numbers than in In2O3. These results clearly demonstrate that In+ exists in a metastable amorphous network, which is the origin of the observed luminescent properties.

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In K-edge XAFS analysis of In2Oα–60ZnO–40P2O5 glass.(a) In K-edge XANES spectra of 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3. (b) FT of EXAFS spectra of the 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3.
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f7: In K-edge XAFS analysis of In2Oα–60ZnO–40P2O5 glass.(a) In K-edge XANES spectra of 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3. (b) FT of EXAFS spectra of the 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3.

Mentions: Although the PL spectra and emissions dynamics suggest the existence of In+ species as ns2-type emissions centres, they do not identify the actual valence state of In. Therefore, the valence state of the In species was estimated using In K-edge X-ray absorption near edge structure (XANES) spectra (Fig. 7a). The shape of the spectrum of the In-doped glass was similar to that of In2O3, while the absorption edge was similar to that of In foil. Because a higher absorption edge indicates a higher oxidation state of the cation, we defined the absorption edge energy E0 as the energy at the zero-crossing of the second derivative. The In K-edge energy of the phosphate glass was higher than that of In, but lower than that of In2O3. /Δ(E0(In foil) – E0(glass, Ar))/ and /Δ(E0(In2O3) – E0(glass, Ar))/ were calculated to be 2.52 eV and 0.71 eV, respectively. Assuming the ΔE0 shift is proportional to the valence of the In species, the valence of In (α value) in the glass was ~2.5, suggesting that 25% of the In3+ was reduced to In+.


Photoluminescence of monovalent indium centres in phosphate glass
In K-edge XAFS analysis of In2Oα–60ZnO–40P2O5 glass.(a) In K-edge XANES spectra of 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3. (b) FT of EXAFS spectra of the 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4555169&req=5

f7: In K-edge XAFS analysis of In2Oα–60ZnO–40P2O5 glass.(a) In K-edge XANES spectra of 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3. (b) FT of EXAFS spectra of the 0.5In2Oα–60ZnO–40P2O5 glass along with In foil and In2O3.
Mentions: Although the PL spectra and emissions dynamics suggest the existence of In+ species as ns2-type emissions centres, they do not identify the actual valence state of In. Therefore, the valence state of the In species was estimated using In K-edge X-ray absorption near edge structure (XANES) spectra (Fig. 7a). The shape of the spectrum of the In-doped glass was similar to that of In2O3, while the absorption edge was similar to that of In foil. Because a higher absorption edge indicates a higher oxidation state of the cation, we defined the absorption edge energy E0 as the energy at the zero-crossing of the second derivative. The In K-edge energy of the phosphate glass was higher than that of In, but lower than that of In2O3. /Δ(E0(In foil) – E0(glass, Ar))/ and /Δ(E0(In2O3) – E0(glass, Ar))/ were calculated to be 2.52 eV and 0.71 eV, respectively. Assuming the ΔE0 shift is proportional to the valence of the In species, the valence of In (α value) in the glass was ~2.5, suggesting that 25% of the In3+ was reduced to In+.

View Article: PubMed Central

ABSTRACT

Valence control of polyvalent cations is important for functionalization of various kinds of materials. Indium oxides have been used in various applications, such as indium tin oxide in transparent electrical conduction films. However, although metastable In+ (5 s2 configuration) species exhibit photoluminescence (PL), they have attracted little attention. Valence control of In+ cations in these materials will be important for further functionalization. Here, we describe In+ species using PL and X-ray absorption fine structure (XAFS) analysis. Three absorption bands in the UV region are attributed to the In+ centre: two weak forbidden bands (1S0 → 3P1,1S0 → 3P2) and a strong allowed band (1S0 → 1P1). The strongest PL excitation band cannot be attributed to the conventional allowed transition to the singlet excited state. Emission decay of the order of microseconds suggests that radiative relaxation occurs from the triplet excitation state. The XAFS analysis suggests that these In+ species have shorter In–O distances with lower coordination numbers than in In2O3. These results clearly demonstrate that In+ exists in a metastable amorphous network, which is the origin of the observed luminescent properties.

No MeSH data available.


Related in: MedlinePlus