Segregation Engineering in MgO Nanoparticle-Derived Ceramics: The Impact of Calcium and Barium Admixtures on the Microstructure and Light Emission Properties

Abstract

Nanostructured segregates of alkaline earth oxides exhibit bright photoluminescence emission and great potential as components of earth-abundant inorganic phosphors. We evaluated segregation engineering of Ca 2+ - and Ba 2+ -admixtures in sintered MgO nanocube-derived compacts. Compaction and sintering transform the nanoparticle agglomerates into ceramics with residual porosities of Φ = 24–28%. Size mismatch drives admixture segregation into the intergranular region, where they form thin metal oxide films and inclusions decorating grain boundaries and pores. An important trend in the median grain size evolution of the sintered bodies with d Ca(10 at. %) = 90 nm < d Ba(1 at. %) = 160 nm < d MgO = 250 nm ∼ d Ca(1 at. %) = 280 nm < d Ba(10 at. %) = 870 nm is rationalized by segregation and interface energies, barriers for ion diffusion, admixture concentration, and the increasing surface basicity of the grains during processing. We outline the potential of admixtures on interface engineering in MgO nanocrystal-derived ceramics and demonstrate that in the sintered compacts, the photoluminescence emission originating from the grain surfaces is retained. Interior parts of the ceramic, which are accessible to molecules from the gas phase, contribute with oxygen partial pressure-dependent intensities to light emission.

Conversion of MgO nanocrystal surfaces into ceramic interfaces: Exsolution of BaO as photoluminescent interface probes

“…15 As a third example, BaO surface segregates stabilized in Ba 2+ containing ZrO 2 or MgO particle powders exhibit great potential as inorganic phosphors, which-depending on the materials processing and excitation profile-produce light emission in the visible light range that can be tuned. 16,17 Traces of highly dispersed BaO can be employed in ceramic matrices as optical probes. Their absorption and emission properties in the UV-Vis range-via photoexcitation of interface elements-can be measured in the diffuse reflectance (DR) mode or photoluminescence (PL) emission (radiative deactivation of excitons at surfaces and interfaces) mode, respectively.…”

“…Relevant to the field of catalyst and photocatalyst design, Ba 2+ admixtures to free surfaces and grain boundary interfaces of nanometer‐sized TiO 2 grains directly impact their coarsening 15 . As a third example, BaO surface segregates stabilized in Ba 2+ containing ZrO 2 or MgO particle powders exhibit great potential as inorganic phosphors, which—depending on the materials processing and excitation profile—produce light emission in the visible light range that can be tuned 16,17 …”

“… 15 As a third example, BaO surface segregates stabilized in Ba 2+ containing ZrO 2 or MgO particle powders exhibit great potential as inorganic phosphors, which—depending on the materials processing and excitation profile—produce light emission in the visible light range that can be tuned. 16 , 17 …”