Zhang Chenning, Uchikoshi Tetsuo, Xie Rong-Jun, Liu Lihong, Cho Yujin, Sakka Yoshio, Hirosaki Naoto, Sekiguchi Takashi
Materials Processing Unit, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan.
Phys Chem Chem Phys. 2016 May 14;18(18):12494-504. doi: 10.1039/c6cp01102k. Epub 2016 Apr 18.
A red phosphor of Sr2Si5N8:Eu(2+) powder was synthesized by a solid state reaction. The synthesized phosphor was thermally post-treated in an inert and reductive N2-H2 mixed-gas atmosphere at 300-1200 °C. The main phase of the resultant phosphor was identified as Sr2Si5N8. A passivation layer of ∼0.2 μm thickness was formed around the phosphor surface via thermal treatment. Moreover, two different luminescence centers of Eu(SrI) and Eu(SrII) in the synthesized Sr2Si5N8:Eu(2+) phosphor were proposed to be responsible for 620 nm and 670 nm emissions, respectively. More interestingly, thermal- and moisture-induced degradation of PL intensity was effectively reduced by the formation of a passivation layer around the phosphor surface, that is, the relative PL intensity recovered 99.8% of the initial intensity even after encountering thermal degradation; both moisture-induced degraded external and internal QEs were merely 1% of the initial QEs. The formed surface layer was concluded to primarily prevent the Eu(2+) activator from being oxidized, based on the systemic analysis of the mechanisms of thermal- and moisture-induced degradation.
通过固态反应合成了Sr2Si5N8:Eu(2+)粉末的红色荧光粉。将合成的荧光粉在300-1200°C的惰性和还原性N2-H2混合气体气氛中进行热后处理。所得荧光粉的主要相被鉴定为Sr2Si5N8。通过热处理在荧光粉表面形成了厚度约为0.2μm的钝化层。此外，合成的Sr2Si5N8:Eu(2+)荧光粉中Eu(SrI)和Eu(SrII)的两个不同发光中心分别被认为是620nm和670nm发射的原因。更有趣的是，通过在荧光粉表面形成钝化层，有效地降低了热和水分引起的PL强度降解，也就是说，即使在经历热降解后，相对PL强度仍恢复到初始强度的99.8%；水分引起的外部和内部量子效率降解仅为初始量子效率的1%。基于对热和水分引起降解机制的系统分析，得出形成的表面层主要防止Eu(2+)活化剂被氧化的结论。
