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

We report the synthesis of β-SiAlON:Eu²⁺ 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(CH₃)₂)₃ and AlCl₃ 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 EuCl₂ with the Al-modified PHPS upon heat-treatment. Gas chromatography-mass spectrometry and thermogravimetry-mass spectrometry analyses revealed that PHPS reacted with Al(OCH(CH₃)₂)₃ and AlCl₃ via the formation of Al-N bonds. Moreover, AlCl₃ reacted with nitrogen-bonded Al alkoxide residue to release 2-chloropropane in an analogy to the non-hydrolytic sol-gel reaction between metal alkoxide and metal chloride. Subsequently, AlCl₃ 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, EuCl₂ reacted with silylamino moiety to form Eu-N bonds at around 850 °C. β-SiAlON:Eu²⁺ phosphors were successfully synthesized by pyrolysis of the precursors under flowing N₂ or NH₃ at 1000 °C, followed by heat treatment at 1800 °C for 1 h under a N₂ gas pressure at 980 kPa. The polymer-derived β-SiAlON:Eu²⁺ (z = 0.55, Eu²⁺ 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.