High thermal stability and colour saturation red-emitting Ba2AGe2O7: Eu3+ (A = Mg, Zn) phosphors for WLEDs

Highlights: • Ba₂AGe₂O₇: Eu³⁺ were synthesized as red-emitting phosphors. • BMGO:0.3Eu³⁺ and BZGO:0.25Eu³⁺ exhibit excellent color purity and thermal stability. • BMGO:0.3Eu³⁺ and BZGO:0.25Eu³⁺ based WLED present excellent luminescence properties. -- Abstract: Two series of Eu³⁺ ions activated high performance red-emitting phosphors Ba_2(1-x)AGe₂O₇: 2xEu³⁺ (A = Mg, Zn, 0 ≤ x ≤ 0.2) were synthesized by high-temperature solid-state procedure. The research results showed that the host lattice Ba₂MgGe₂O₇ possess higher band gap than that of Ba₂ZnGe₂O₇, and all the Ba_2(1-x)MgGe₂O₇: 2xEu³⁺ (BMGO: 2 xEu³⁺, 0 ≤ x ≤ 0.2) and Ba_2(1-x)ZnGe₂O₇: 2xEu³⁺ (BZGO: 2 xEu³⁺, 0 ≤ x ≤ 0.2) phosphors crystallized in a tetragonal unit cell with the space group of P421 m (113). Compared with other phosphors in the same series, the samples BMGO: 0.30 Eu³⁺ and BZGO: 0.25 Eu³⁺ presented the highest absorption intensity when monitoring at 616 nm under 395 nm excited, respectively. Moreover, the samples BMGO: 0.30 Eu³⁺ and BZGO: 0.25 Eu³⁺ not only exhibited high color purity of 90% and 90.3%, respectively, but also possess excellent thermal stability. Unsurprisingly, the WLED devices based on BMGO: 0.30 Eu³⁺ and BZGO: 0.25 Eu³⁺ as the red-emitting components displayed good luminescence properties, especially the color rendering index (CRI, R_a) R₉ represented the saturation of colour of illuminated objects exhibited a high value of 89.6 and 82.3, respectively. In contrast, the WLED device based on BMGO: 0.30 Eu³⁺ as red-emitting phosphors presented better electroluminescence performances than those of BZGO: 0.25 Eu³⁺ on account of its much favorable crystal structure, PL performance and thermal stability.