Mn 2+ doped Ca1-xSrxCN2 phosphors were synthesized by a solid-state reaction in only 1 h under NH3 atmosphere at 700 °C from doped calcium carbonate and carbon nitride as precursors. The samples were characterized by powder X-ray diffraction, scanning electron microscopy and their diffuse reflectance and luminescence properties were investigated in order to evaluate the potential of such systems as red phosphors. All pure and well-crystallized Mn 2+ doped samples exhibit broad red emission around 680 nm when excited at 270 nm at room temperature corresponding to the 4 T1g( 4 G) → 6 A1g( 6 S) transition. Maximum emission in CaCN2 : Mn is obtained for Mn 2+ content of 4 %mol and is stable up to 343 K and then shows a 20 % decrease at 393 K. Finally, the progressive substitution of Sr 2+ for Ca 2+ evidences a solid solution domain between CaCN2 and β-SrCN2 with continuous increase of the crystal lattice dimensions. However, such substitution has no impact on the wavelength emission but leads to a decrease of the luminescence efficiency of the phosphor.
An alternative general approach to synthesize carbodiimide materials using carbon nitride as precursor is proposed. This new facile synthetic route was illustrated by the preparation of single phases α-SrCN 2 and β-SrCN 2 in a reproducible and effective manner via the substitution of barium and calcium for strontium. Structural characterizations and optical properties of Eu 2+ doped SrCN 2 polymorphs were investigated on the bases of high-resolution X-ray powder diffraction and photoluminescence analyses to evaluate the potential of such systems as red phosphors. All Eu 2+ doped samples exhibit intense red emission in the 620-630 nm range when excited at 440 nm at 77 K with little impact of the crystal lattice on emission wavelength. However, calcium and barium substitutions for strontium strongly impact the emission intensity and the emission width respectively and all doped samples have their emission intensity reduced by 50 % around 80-90 K and totally quenched at RT.
Ce3+-doped and Ce3+/Mn2+ co-doped calcium carbodiimide (CaCN2) phosphors were synthesized from doped calcium carbonate and carbon nitride by a solid-state reaction at 700 °C under flowing NH3 using a very short reaction time (1 h). The samples were characterized by powder X-ray diffraction, scanning electron microscopy and their diffuse reflectance and luminescence properties were investigated. Single-doped CaCN2:Ce3+ exhibits a blue emission under near-ultraviolet activation (386 nm) corresponding to the 5d1 → 2F5/2 and 5d1 → 2F7/2 transitions of Ce3+. Maximum emission is obtained at temperatures lower than 150 K and then progressively decreases up to 387 K, with an 80% drop in the emission at room temperature. Efficient energy transfers from Ce3+ to Mn2+ via a non-radiative dipole–dipole mechanism are evidenced for the co-doped samples, leading to various colored phosphors under near-ultraviolet activation (386 nm). The emission color of the obtained phosphors can be modulated from blue to red through a shade of white depending on the sensitizer/activator ratio.
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