Chemical route for synthesis of β-SiAlON:Eu2+ phosphors combining polymer-derived ceramics route with non-hydrolytic sol-gel chemistry

Abstract

We report the synthesis of β-SiAlON:Eu 2+ phosphors from novel single source precursors in which strictly controlled chemical composition is established at molecular scale. The two-step synthesis occurs by the chemical modification of perhydropolysilazane (PHPS) with Al(OCH(CH 3 ) 2 ) 3 and AlCl 3 in xylene at room temperature to 140 °C to introduce Al in the PHPS network while controlling the oxygen content followed by the reaction of EuCl 2 with the Al-modified PHPS upon heat-treatment. Gas chromatography-mass spectrometry and thermogravimetry-mass spectrometry analyses revealed that PHPS reacted with Al(OCH(CH 3 ) 2 ) 3 and AlCl 3 via the formation of Al-N bonds. Moreover, AlCl 3 reacted with nitrogenbonded Al alkoxide residue to release 2-chloropropane in an analogy to the non-hydrolytic sol-gel reaction between metal alkoxide and metal chloride. Subsequently, AlCl 3 acted as a Lewis acid catalyst to promote the Friedel-Craft alkylation between xylene solvent and the 2-chloropropane formed in-situ to afford dimethylcumene. On the other hand, EuCl 2 reacted with silylamino moiety to form Eu-N bonds at around 850 °C. β-SiAlON:Eu 2+ phosphors were successfully synthesized by pyrolysis of the precursors under flowing N 2 or NH 3 at 1000 °C, followed by heat treatment at 1800 °C for 1 h under a N 2 gas pressure at 980 kPa. The polymer-derived β-SiAlON:Eu 2+ (z = 0.55, Eu 2+ 0.37 at%) exhibited green emission under excitation at 410 or 460 nm, and the green emission intensity under the excitation at 410 nm was found to be increased by reducing the carbon and chlorine impurities through the polymer-derived ceramics route investigated in this study.

Polymer‐derived β‐SiAlON:Eu2+ phosphors

“…The z values calculated for the A66E1 and A69E1 by the theoretical β‐SiAlON formula, Si 6− z Al z O z −2 y N 8− z +2 y : y Eu 2+ , 8 were .64 and .78, respectively. The resulting nominal chemical composition was expressed by the modified formula, Si 6− z Al z O z −2 y + δ N 8− z +2 y + γ : y Eu 2+ 19,20 . The value of differences, δ and γ , were also listed in this table.…”

“…The handling of the chemicals and reagents was performed under dry argon (Ar) atmosphere using standard Schlenk techniques. Single‐source precursor synthesis was conducted according to our established procedures 19,20 …”

“…The chemical reactions during the precursor pyrolysis up to 1000°C were monitored by the TG–MS analyses under He flow (model STA7200, Hitachi, Tokyo, Japan) according to the procedure performed in our previous studies 19,20 …”

“…For each sample, the Al/Si and Eu/Si ratios were evaluated as an average value of the mapping scans conducted for at least five different areas randomly selected. Then, the chemical composition of the polymer‐derived SiAlON‐based samples was determined as follows 19,20 : $$$$\begin{eqnarray}{\rm{wt}}\% {\rm{ }}\left( {{\rm{Si}} + {\rm{Al}} + {\rm{Eu}}} \right) &=& 100\% {\rm{ }} - {\rm{ wt}}\% {\rm{ }}\left( {\rm{C}} \right)\nonumber\\ && -\, {\rm{wt}}\% {\rm{ }}\left( {\rm{N}} \right) - {\rm{wt}}\% {\rm{ }}\left( {\rm{O}} \right)\end{eqnarray}$$$$…”

“…Moreover, in this PDCs route, by the partial replacement of the Al(OCH(CH 3 ) 2 ) 3 with aluminum trichloride (AlCl 3 ), the oxygen content in the 1000°C‐pyrolyzed product, amorphous SiAlEuON was successfully controlled independently with the Al content (Equation 2), 20 , which offers an opportunity to investigate the effect of the chemical composition on the β‐SiAlON:Eu 2+ phosphors formed in situ in more detail.…”