Synthesis of silicate apatite phosphors with enhanced luminescence via optimized precipitation technique through pH control

Silicates with apatite structure have become one of the most promising candidates for solid-state lighting applications. Herein we report the synthesis of pure apatite Ca2Y7.76Ce0.12Tb0.12(SiO4)(6)O-2 phosphors with enhanced luminescence via a simple precipitation method. The aim of this study is to optimize the precipitation reaction through pH control and TEOS amount. In this respect, different types of precursors were prepared by precipitation between yttrium-calcium-cerium-terbium nitrates and NaOH at various pH. The extremely complex decomposition processes of precursors are discussed based on thermogravimetric analysis. The structure, morphology, surface state and porosity of both precursors and phosphors were investigated based on FTIR, XRD, SEM and BET. It was found that the crystallinity degree of the precursors decreases from 36% to 5% with the increase of pH from 7 to 11. After the thermal treatment, the phosphors become pore-less and well crystallized with crystallite sizes up to 106 nm. The phase composition of the phosphors strongly depends on the pH during the precipitation. Synthesis performed with 40% excess of TEOS at pH 11 led to phosphors with pure apatite structure and enhanced luminescence. Under excitation with 365 nm the apatite phosphors exhibits a broad emission band in the range of 350-480 nm, due to transitions in Ce(3+)and narrow lines in range of 480-650 nm specific for transitions in Tb3+. [GRAPHICS] .