title: Prevention of thermal- and moisture-induced degradation of the photoluminescence properties of the Sr2Si5N8:Eu(2+) red phosphor by thermal post-treatment in N2-H2.
abstract: 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.
authors.affiliation: Materials Processing Unit, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan. UCHIKOSHI.Tetsuo@nims.go.jp.
authors.forename: Chenning
authors.initials: C
authors.lastname: Zhang
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Uchikoshi
authors.forename: Rong-Jun
authors.initials: RJ
authors.lastname: Xie
authors.forename: Lihong
authors.initials: L
authors.lastname: Liu
authors.forename: Yujin
authors.initials: Y
authors.lastname: Cho
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Sakka
authors.forename: Naoto
authors.initials: N
authors.lastname: Hirosaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Sekiguchi