Novel red emitting phosphors Ca8MgSm1–х(PO4)7:xEu3+ with whitlockite-type structure were prepared by a high temperature solid-state reaction in air. Powder X-ray diffraction (PXRD), photoluminescence spectra, and fluorescence decay were used to characterize the structure and luminescence properties. All samples were found to have the expected rhombohedral structure with R3¯c space group. The non-polar space group is also confirmed by a photoluminescence study. This space group allows forbidden transitions for Eu3+. The presence of only one Shtark component in 5D0–7F0 confirms the presence of only one non-equivalent site containing Eu3+ ions. The high intensity of the transition ratio 5D0–7F2/5D0–7F1 establishes the strongly disordered environment of the Eu3+ ions. Thus, M1–M3 sites in the host matrix are occupied by Ca2+, Sm3+, and Eu3+ ions, whereas M5 is fully occupied by Mg2+. The optimal concentration was found with x = 0.75 in Ca8MgSm1–х(PO4)7:xEu3+ phosphors. The emitting of Sm3+ was depressed due to the high intensity of Eu3+ luminescence; however, the contribution of Sm3+ is manifested in the energy transfer process and shift of CIE coordinates. Furthermore, the CIE chromaticity coordinate of as-prepared Ca8MgSm0.25(PO4)7:0.75Eu3+ (x = 0.650; y = 0.345) is close to the standard red-emitting point (x = 0.67, y = 0.33). The experimental data indicate that Ca8MgSm1–х(PO4)7:xEu3+ upon excitation by near-UV radiation is a promising red phosphor for white-light-emitting diodes.
- Red phosphors
- Whitlockite-type structure