Sr8MSm1-x Eu x (PO4)7 phosphors derived by different synthesis routes: Solid state, sol-gel and hydrothermal, the comparison of properties

Highlights: • Phosphors with whitlockite-type structure Sr₈M²⁺Sm_1-(PO₄)₇:xEu³⁺, M = Mg²⁺, Zn²⁺ were synthesized by three type of routes. • The influence of the synthetic route on the luminescent properties was revealed. • Solid-state reaction method leads to better crystallinity, and to improvement of the luminescent proprieties. -- Abstract: A series of new Sr-based phosphors Sr₈M²⁺Sm_1-(PO₄)₇:xEu³⁺, M = Mg²⁺, Zn²⁺ with β-Ca₃(PO₄)₂-type structure was synthesized and studied. The Sr₈MgEu(PO₄)₇ was obtained by three types of synthetic routs: high temperature solid-state, hydrothermal and sol-gel methods. The influence of synthesis routes and annealing conditions on luminescent properties was studied and analyzed taking into account the data on average crystallite size and grain size determination. It was shown that the synthesis method has a defining role on the phosphor's properties. The solid-state route gives the best powders crystallinity and the highest intensity of emission. The samples were characterized by strong emission in visible region at 615 nm originating from ⁵D₀ → ⁷F₂ transition of Eu³⁺ and 600 nm originating from the ⁵G_5/2 → ⁴H_7/2 transition of Sm³⁺. Also, it was revealed that Zn-substituted samples exhibit higher intensity than Mg-containing ones due to larger particle size and lower scattering of light and higher light absorption. Photoluminescence decay curves were measured and the dependence of decay times on activator concentrations was revealed. The CIE chromaticity coordinates were close to red standard. The prototypes of LED devices were characterized by strong emission with warm correlated color temperature. The investigated compounds can be used as a potential commercial phosphor for solid-state lighting application.