Role of the Eu3+ Distribution on the Properties of beta-Ca-3(PO4)(2) Phosphors: Structural, Luminescent, and Eu-151 Mossbauer Spectroscopy Study of Ca9.5-1.5xMgEux(PO4)(7)
The series of β-Ca3(PO4)2-type phosphors Ca9.5–1.5xMgEux(PO4)7 were synthesized by a solid-state route. Observation of the proper Eu3+ ion distribution in the Ca9.5Mg(PO4)7 host matrix was made by a direct method using 151Eu Mössbauer spectroscopy in combination with X-ray analysis and dielectric and luminescent spectroscopy. The photoluminescence properties were studied in detail. The samples exhibit an exceptionally narrow-band red emission according to the dominant 5D0 → 7F2 transition and fulfill the industrial requirements for high-energy-efficiency red phosphors. The contribution of Eu3+ ions in different crystal sites to the luminescent properties is discussed in detail. The difference of the excitation of Eu3+ in the M1 and M2 sites was revealed by photoluminescence excitation spectra in accordance with structure refinement. The temperature dependence of the luminescence intensity was studied. Different tendencies in the thermal behavior of emission lines allow one to consider the studied compounds as phosphors suitable for luminescence thermometry. The measured quantum yield for Ca9.5–1.5xMgEux(PO4)7 shows excellent results and reaches 63%.