The microstructurally-induced heterogeneous stress fields arising in a series of Cr-doped polycrystalline alumina components are mapped with sub-micrometer sub-grain size resolution using fluorescence microscopy. and grain boundaries. The mean axis. As a consequence of the octahedral geometry, the ruby fluorescence is usually split into a doublet consisting of two closely spaced fluorescent lines, designated R1 and R2, with energies, specified in wavenumbers, of approximately 14403 cm?1 and 14433 cm?1, respectively (the wavelengths are approximately 694 nm). Early experiments showed that further distortion of the octahedral sites by application of stress to the corundum structure leads to shifts 817204-33-4 IC50 in these energies [3, 4], as do changes in temperature [5, 6] and composition [7], which also distort the octahedra. The intensity of the photoluminescence is usually strongly dependent on the polarization direction of the excitation light relative to the orientation of the octahedral sites and thus the orientation of the crystal [1, 2]. Measurements of the energy shifts have been applied to assess the stress state in single crystal (ruby or sapphire) and polycrystalline Al2O3 materials. (Transparent sapphire and translucent or opaque white polycrystalline Al2O3 usually contain enough trace Cr to make such measurements possible.) Initial applications focused on the calibration of the fluorescent line shifts with hydrostatic pressure in single crystals, such that the incorporation of small ruby chips into diamond anvil cells (DACs) enabled the pressure to be measured during high pressure experiments [8-12]. The coefficient linearly relating the shift in energy, , to the pressure, [GPa], broadly consistent with earlier hydrostatic [13, 14] and uniaxial compression measurements [3, 4, 15]. The first to apply measurement of the fluorescence shifts to polycrystalline 817204-33-4 IC50 Al2O3 was Grabner [16], who developed a crystallographic analysis to describe the shifts for an arbitrary tension. Grabner mixed this analysis using the change coefficients motivated under uniaxial compression [3, 4] to measure the residual tension state due to thermal enlargement anisotropy from the constituent corundum grains in polycrystalline Al2O3: tensile and compressive strains of order a huge selection of megapascal had been inferred, in keeping with computations and similar, afterwards, observations [17, 18]. The next work of Clarke extended the way of applications involving polycrystalline Al2O3 significantly. Specifically, Clarke and co-workers: confirmed that the change coefficients motivated in compression had been also valid in stress [19, 20]; sophisticated and expanded the evaluation of Grabner to allow interpretation of shifts and distributions of shifts due to inhomogeneous tension fields [20]; sophisticated determination from the change coefficients being a function of crystal orientation and confirmed that shifts aren’t affected by program of shear tension [21]; and, quantified the polarization dependence from the photoluminescent R-line intensities [22]. Co-workers and Clarke used their ways to measure strains in fibres in matrices [23-25], strains in polycrystalline Al2O3-ZrO2 laminates and composites [26-28], and stress in wrinkled oxide coatings shaped on metal areas [29-33]. Pezzotti and co-workers also used 817204-33-4 IC50 the fluorescence change technique to measure tension distributions in Al2O3-ZrO2 composites [34] (just like [35]), but moreover made the initial direct perseverance of strains in bridging ligaments behind split ideas in large-grained 817204-33-4 IC50 polycrystalline Al2O3 [36] and in a series of Al2O3 materials with microstructures tailored with Al2O3 platelets [37, 38] and metal particles [37, 39-41] to maximize bridging. More recently, Todd and colleagues have used the methodology to measure stresses in polycrystalline Al2O3 and Al2O3-SiC composites [42], including the effects of surface grinding [43, 44], and proximity to indentations [45, 46] and high strain rate impacts [47] in polycrystalline Al2O3, Al2O3-SiC, and Al2O3-ZrO2. Despite the above advances and exhibited applications, very few works have used fluorescence shift measurements to generate images (two-dimensional, 2-D, maps) of stress heterogeneity in Al2O3 systems. Most measurements have been single point measurements (for 817204-33-4 IC50 example [21, 48]) using optical probe spot diameters of about 10 m, or large area measurements with spot diameters up to 100 m encompassing and averaging the responses of many grains in polycrystals (for example, [16, 19, IRAK3 20, 26-28, 35, 49]). In some cases, a series of point measurements.