Structure, optical properties and preferential site substitution of Eu$^{3+}$ activated Ca$_8$NaBi(PO$_4$)$_6$F$_2$ red emitting phosphors prepared by modified Pechini process - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Luminescence Année : 2022

Structure, optical properties and preferential site substitution of Eu$^{3+}$ activated Ca$_8$NaBi(PO$_4$)$_6$F$_2$ red emitting phosphors prepared by modified Pechini process

Résumé

Eu3+-doped and undoped Ca8NaBi(PO4)6F2:xEu (x = 0.01 – 0.5) apatite phosphors have been synthesized at 900 °C by the modified Pechini process.Their structural and morphological characteristics were determined by XRD, TEM and Raman spectroscopy. The structure of the host matrix was refined by the Rietveld method: Ca8NaBi(PO4)6F2 crystallizes in hexagonal class, sp. gr. P63/m, a = b =9.3980(6) Å, c = 6.9039(9) Å and γ = 120°). The electronic structure was simulated revealing an indirect bandgap of 3.46 eV. Eu3+ ions in the host matrix replace for the Bi3+ ones in two types of sites: M1 (C3 symmetry and IX-fold oxygen coordination) and M2 (CS symmetry and VII-fold coordination by one fluoride and six oxygens). The doping induces a redistribution of Eu3+ ions over the M1 and M2 sites in favor of the former species. The transition probabilities for Eu3+ ions in M2 sites were determined using the Judd-Ofelt theory yielding a radiative lifetime of 2.21 ms. It was found that phosphors exhibit relatively weak luminescence quenching. The CIE 1931 color coordinates for the compound with x = 0.35 Eu are (0.648,0.352) falling in the red region and corresponding to a correlated color temperature of 2919 K and a color purity of >96%. The thermal stability of the phosphor was studied until 400 °C (the determined activation energy is 0.70 eV) indicating a redistribution of ions in favor of the M2 sites at high temperatures. Ca8NaBi(PO4)6F2:xEu apatites are promising as red phosphors for white-light LEDs.
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hal-03858685 , version 1 (17-11-2022)

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Sami Slimi, Pavel Loiko, Anna Volokitina, Kirill Bogdanov, Rosa Maria Solé, et al.. Structure, optical properties and preferential site substitution of Eu$^{3+}$ activated Ca$_8$NaBi(PO$_4$)$_6$F$_2$ red emitting phosphors prepared by modified Pechini process. Journal of Luminescence, 2022, 241, pp.118523. ⟨10.1016/j.jlumin.2021.118523⟩. ⟨hal-03858685⟩
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