Red-emitting Lu3Al5O12: Mn transparent ceramic phosphors: valence state evolution studies of Mn ions

Red-emitting YAG: Ce, Mn transparent ceramics for warm WLEDs application

“…After Mn 2+ -Si 4+ pairs were introduced into the YAG:Ce ceramics, it can be seen from Fig. 6(b) that two obvious emission bands aside from Ce 3+ emission band are observed at 590 and 745 nm, which is similar to the PL spectrum of Mn 2+ -doped YAG phosphors and PIGs phosphor [27,28,31]. As for the emission band of Mn 2+ at 528 nm, its intensity is so weak in comparison to strong Ce 3+ emission intensity that it cannot be observed.…”

“…Besides, it is commonly accepted that Mn with different valences emit different luminescence properties. Aside from the aforementioned emission wavelength of Mn 2+ ions, Mn 3+ emission bands are observed peaked at 608 and 760 nm attributed to 5 T 2 → 5 E transition and Mn 4+ emission bands are observed peaked at 668 nm attributed to 2 E→ 4 A 2 [26,28]. In this work, the luminescence wavelength of Mn 3+ and Mn 4+ can not be observed and it is worth noting that Mn 2+ is oxidized little or nothing in the vacuum environment, and thus almost Mn 2+ ions exist in YAG:Ce,Mn transparent ceramics.…”

“…Furthermore, the YAG:Ce 3+ ,Mn 2+ ,Si 4+ phosphors embedded in glass ceramics (PIGs) were also prepared as a chromaticallytunable luminescent material, in which the CCT and LE reach 4954-3753 K and 80.8-60.3 lm/w, respectively [27]. Moreover, Lu 3 Al 5 O 12 :Mn (LuAG:Mn) transparent ceramics with red-emitting at 600-700 nm have been reported [28]. In summary, optimized emission with low CCT value can be achieved by the strategy of co-doping of Mn 2+ in YAG:Ce 3+ system.…”

Valence State Control of Manganese in MgAl2O4:Mn4+ Phosphor by Varying the Al2O3 Crystal Form

“…MgAl2O4:Mn 2+ [15] 和 MgAl2O4:Mn 4+ [7] 荧光粉的激发 光谱一致， 各激发峰分别对应于 Mn Zhang 等 [19] 曾报道 Lu3Al5O12:Mn 透明陶瓷中同 时出现 Mn 4+ /Mn 2+ /Mn 3+ 混合价态的现象并研究了后 续热处理对其中锰离子价态的影响：经 1750 ℃下 6 h 真空烧结后所得透明陶瓷中锰离子为 Mn 2+ ，再经 1400 ℃ 空气中退火 5 h 后 得 到 多 价 态 共 存 Lu3Al5O12:Mn 2+/3+/4+ 陶瓷。 该课题组 [22] 进一步对比了 退火气氛(空气和氧气)对 Lu3Al5O12:Mn 荧光透明陶 5 Photoluminescence emission spectra (λex=365 nm) of the MgAl2O4:Mn phosphors using the Al2O3 with different α/(α+γ) ratios either annealed at 1000 ℃ for 10 h (a) or annealed at 1000 ℃ for 10 h and at 1200 ℃ for another 10 h, I651 nm/I520 nm ratios calculated from the luminescence spectra of the MgAl2O4:Mn phosphors (both as-prepared and post-annealed) (c)…”

“…Mn 2+ 绿光发 光和 651 nm 处 Mn 4+ 红光发光外， 还观测到位于 687 nm 的窄带深红光发光和位于 740 nm 的宽带近红外 光发光。其中，位于 687 nm 的窄带深红光发光与 Chi 等 [18] 报道的 MgAl2O4:Cr 3+ 荧光粉的发射光谱一 致；且从该文所报道激发光谱看，365 nm 可有效激 发 MgAl2O4:Cr 3+ 的 4 A2→ 4 T1 自旋允许跃迁。考虑到 Cr 与 Al 为同主族元素，Cr 3+ 是 Al2O3 原料中常见的 难去除残存杂质离子，该 687 nm 处微弱发光应是 Al2O3 原料中 Cr 3+ 杂质引起的 MgAl2O4:Cr 3+ 的 2 E→ 4 A2 自旋禁戒跃迁。 而 740 nm 处的宽带红外光发光， 与 Zhang 等[19] 报道的 Lu3Al5O12:Mn 4+/3+/2+ 荧光陶瓷 中所测阴极射线发光光谱中 Mn 3+ 的发光特征一致 Mn 2+ 的吸收。而当铝源中 α/(α+γ)比例为 0 时，所合成 MgAl2O4:Mn 的漫反射 光谱中除 400 nm 附近吸收谷(对应于 Mn 4+ 离子…”