Mechanoluminescence (ML) is the phenomenon describing the emission of light during mechanical action on a solid, leading to applications such as pressure sensing, damage detection and visualization of stress distributions. In most cases, this mechanical action releases energy that was previously stored in the crystal lattice of the phosphor by means of trapped charge carriers. A drawback is the need to record the ML emission during a pressure event. In this work, we provide a method for adding a memory function to these pressure-sensitive phosphors, allowing an optical readout of the location and intensity of a pressure event in excess of 72 h after the event. This is achieved in the BaSi2O2N2:Eu2+ phosphor, where a broad trap depth distribution essential for the process is present. By merging optically stimulated luminescence (OSL), thermoluminescence (TL) and ML measurements, the influence of light, heat and pressure on the trap depth distribution is carefully analysed. This analysis demonstrates that mechanical action can not only lead to direct light emission but also to a reshuffling of trap occupations. This memory effect not only is expected to lead to new pressure sensing applications but also offers an approach to study charge carrier transitions in energy storage phosphors.
Ultrasound is used extensively in medical imaging and therapy, non‐destructive testing, flow sensing, underwater range assessment, and acoustic microscopy. To ensure the accuracy of these techniques, detailed knowledge of the acoustic pressure field produced by the ultrasonic transducer is required. This paper proposes a functional polymer membrane loaded with ultrasound‐activated luminescent microparticles. The semitransparent membrane makes use of the luminescent properties of BaSi2O2N2:Eu2+ to convert ultrasonic pressure into visible light in a fast and straightforward way, through a process termed acoustically produced luminescence (APL). APL is shown to work within a wide range of acoustic frequencies (1–25 MHz) and pressures (50 kPa–4.5 MPa), and enables a quantitative characterization of ultrasound fields with a lateral spatial resolution below 200 µm. At the investigated pressures and frequencies, the light generation mechanism is essentially related to ultrasonic heating rather than mechanical stimulation. These membranes offer effective field mapping possibilities, much faster than conventional time consuming point‐by‐point hydrophone scanning.
This is the electronic supplementary information (ESI) for the article entitled 'Relating Structural Phase Transitions to Mechanoluminescence: The Case of the Ca 1−x Sr x Al 2 Si 2 O 8 :1%Eu 2+ ,1%Pr 3+ Anorthite'. It includes supplementary information on (1) the scanning electron microscopy (SEM) images of anorthites, (2) their cell parameters from Rietveld refinement, (3) methods of extracting electron population functions and (4) TL curves as a function of Delay time for x Sr = 0.00 and 0.10.
Abstract:The monitoring of stress changes in structural components under various kinds of dynamical loading is crucial for the assessment of their integrity and lifetime. In addition to many methodologies available, such as strain gauges, optical fiber sensors, X-Ray diffraction and digital image correlation, we introduce a novel non-contact method to visualize stress distributions based on mechanoluminescence (ML). ML is a phenomenon occurring in some materials that emit light upon an applied stress level. In this paper, we develop the ML material (Ca0.4Sr0.6)Al2Si2O8:1%Eu 2+ ,1%Ho 3+ , a glow-in-the-dark material, to visualize stress distribution in a disc, as well as the stress field of an ultrasonic transducer. The properties of defects in the ML phosphors, which are responsible for ML in this material, are vital for stress visualization.
This is the electronic supplementary information (ESI) for the article entitled 'Relating Structural Phase Transitions to Mechanoluminescence: The Case of the Ca 1−x Sr x Al 2 Si 2 O 8 :1%Eu 2+ ,1%Pr 3+ Anorthite'. It includes supplementary information on (1) the scanning electron microscopy (SEM) images of anorthites, (2) their cell parameters from Rietveld refinement, (3) methods of extracting electron population functions and (4) TL curves as a function of Delay time for x Sr = 0.00 and 0.10.
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