2. Points of Interest Synthesis Crystallography Physical Properties

3. Synthesis of Nanoparticles Chemical vapour deposition (CVD) Flow reactor: Attain almost perfect cubic shape after sintering under high vacuum

4. Crystallography Both MgO and CaO adopt the rock-salt structure Mixtures of the oxides (eg. Mg x Ca 1-x O) are immiscible up to 1900K as a result of ion radius (Mg: 0.72, Ca: 1.0Å) Free energy of formation is positive, predict thermodynamic instability This does not apply for nano-meter sized crystals Stoichiometries 0 < x < 0.12 follow Vegard’s Law (lattice parameters change linearly with composition) At x > 0.12, CaO migrates to surface (predicted by calculation) but is not periodic (XRD)

5. Luminescence Excitation with UV light (290 nm): MgO: little luminescent properties CaO: intense emission band at 410 nm Mg 0.9 Ca 0.1 O: intense emission at 430 nm, bright glow Mg 0.8 Ca 0.2 O: similar to CaO

6. Conclusions CVD allows the formation of mixed alkaline earth oxides Irregular surface (containing Ca 2+, Mg 2+ and O 2- ions) gives rise to red- shifted light emission and enhanced electron transition probability Choice of dopant (Ca 2+, Sr 2+, Ba 2+, etc) and concentration controls optical properties