Abnormal Eu[sup.3+] → Eu[sup.2+] Reduction in Ca[sub.9−x]MnIx/IEu[sub.7] Phosphors: Structure and Luminescent Properties

• Published in: Materials 2023-02, Vol.16 (4)
• Main Authors: Sipina, Elena V, Spassky, Dmitry A, Krutyak, Nataliya R, Morozov, Vladimir A, Zhukovskaya, Evgenia S, Belik, Alexei A, Manylov, Mikhail S, Lazoryak, Bogdan I, Deyneko, Dina V
• Format: Article
• Language: English
• Subjects: Light-emitting diodes
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16041383

β-Ca[sub.3](PO[sub.4])[sub.2]-type phosphors Ca[sub.9−x]MnxEu(PO[sub.4])[sub.7] have been synthesized by high-temperature solid-phase reactions. The crystal structure of Ca[sub.8]MnEu(PO[sub.4])[sub.7] was characterized by synchrotron X-ray diffraction. The phase transitions, magnetic and photoluminescence (PL) properties were studied. The abnormal reduction Eu[sup.3+] → Eu[sup.2+] in air was observed in Ca[sub.9−x]MnxEu(PO[sub.4])[sub.7] according to PL spectra study and confirmed by X-ray photoelectron spectroscopy (XPS). Eu[sup.3+] shows partial reduction and coexistence of Eu[sup.2+]/[sup.3+] states. It reflects in combination of a broad band from the Eu[sup.2+] 4f[sup.6]5d[sup.1] → 4f[sup.7] transition and a series of sharp lines attributed to [sup.5]D[sub.0] → [sup.7]F[sub.J] transitions of Eu[sup.3+]. Eu[sup.2+]/Eu[sup.3+] ions are redistributed among two crystal sites, M1 and M3, while Mn[sup.2+] fully occupies octahedral site M5 in Ca[sub.8]MnEu(PO[sub.4])[sub.7]. The main emission band was attributed to the [sup.5]D[sub.0] → [sup.7]F[sub.2] electric dipole transition of Eu[sup.3+] at 395 nm excitation. The abnormal quenching of Eu[sup.3+] emission was observed in Ca[sub.9−x]MnxEu(PO[sub.4])[sub.7] phosphors with doping of the host by Mn[sup.2+] ions. The phenomena of abnormal reduction and quenching were discussed in detail.