Spark plasma sintering of nano magnesia: Processing parameters influencing optical properties

Densification of laboratory-made nanocrystalline magnesium oxide powder synthesized by gel combustion method was performed through spark-plasma-sintering using both pulsed and unpulsed DC. Grain growth in post-sintered microstructure limited within 200 nm. Photoluminescence study through Gaussian splitting of broad band emission spectra reveals that SPS-processing enhances luminescence in bulk specimens because of oxygen vacancies generated under reducing atmosphere during sintering. Influence of heat treatment on the defect-induced photoluminescence behaviour was investigated. Decrease in emission intensity with post-sintering annealing temperature, caused by decreasing concentration of colour centres due to oxygen recombination process, has been found to be related to the improvement in transmittance property.