Photoluminescence Piezospectroscopy

Photoluminescence piezospectroscopy is an accurate measurement method to determine nanoscale stress distributions and surface defects that control device performance and reliability, that is performance over the service life of biomaterials such as hydroxyapatite coatings and implants. 

This method is based on measuring the shift of the optical energy levels of fluorescent elements such as Cr3+ in response to a change of the stress state. This results in undergo as the result of altering the distance of ions within the strained crystal structure of the host lattice (Yu and Clarke, 2002). Equipment used to record photoluminescence spectra include confocal laser-Raman spectrometers equipped with a liquid nitrogen cooled CCD detector and a motorised X-Y microscope table to allow point-by-point mapping. 

Assuming that for in-plane biaxial stress rrxx = a = ab and ozz = 0 (Ma and Clarke, 1993), the residual stress can be estimated following Margueron and Lep-outre (2003) to be rb(GPa) as 0.2 Av(cm 1) for the corundum structure. 

An experimental example will be presented below dealing with thermally sprayed mullite (SAljOj SiOj AljC -SiC solid solution) coatings (Heimann, 

Presently, methods are being developed that focus on the use of superresolution confocal Raman microscopy (CRM), electron back-scattered diffraction (EBSD), and, in combination with high-resolution XRD, to identify and measure the stress distributions of structures and defects that control 

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Raman photoluminescence piezospectroscopy of bone, teeth and artificial joint materials has been reviewed by Pezzotti (2005) with emphasis placed on confocal microprobe techniques. Characteristic Raman spectra were presented and quantitative assessments of their phase structure and stress dependence shown. Vibrational spectroscopy was used to study the microscopic stress response of cortical bone to external stress (with or without internal damages), to define microscopic stresses across the dentine - enamel junction of teeth under increasing external compressive masticatory load and to characterise the interactions between prosthetic implants and biological environment. Confocal spectroscopy allows acquisition of spatially resolved spectra and stress imaging with high spatial resolution (Green etal., 2003 Pezzotti, 2005 Munisso etal., 2008). 

Figure 15 (A) Frequency shift of photoluminescence piezospectroscopy (PLPS) measured at room temperature in the course of cyclic oxidation of EBPVD samples. (B) Progress of interfacial separation after different cycles at 1150°C. Redraw from [88],...

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