Ever since the discovery of SrAl2O4:Eu,Dy persistent afterglow material, that can intensively glow up to 20 h, the mechanism of long-lasting luminescence has been a popular area of research. The research is focused on discovering the mechanism of persistent luminescence in order to prolong the duration and intensity of afterglow in a controlled way. Although most researchers agree on the general things, there are still many unclarities and ambiguities to discuss upon. This review paper briefly sketches in the highlights of past research on the luminescence mechanism in SrAl2O4:Eu,Dy, mainly focusing on the research conducted in the past decade dedicated to clearing these ambiguities. This paper provides an overview of the latest persistent luminescence mechanisms offered by researchers.

Temperature dependence of the afterglow of persistent luminescence material SrAl 2 O 4 :Eu,Dy is a major problem for outdoor low temperature applications. Therefore this publication deals with tailoring the material for better outdoor use by exploring the second mechanism, that is involved in the afterglowcharge tunnelling from the trapping center to the luminescence center. Structure, morphology, emission and thermally stimulated luminescence properties have been measured for SrAl 2 O 4 :Eu,Dy samples with different added boron percentage. The results indicate a change in morphology of the samples with increasing boron concentration, as well as a change in afterglow times. The low temperature luminescence intensity and afterglow time dependence of boron addition turns out to be different from the room temperature luminescence intensity and afterglow time dependence from boron concentration. Boron addition in necessary amount plays a key role to creating trapping centers in the material that are located spatially close to the luminescence center thus making the material afterglow possible even in low temperatures.

SrAl 2 O 4 : Eu, Dy, B particles were added in a phosphate glass (90NaPO 3-10NaF (in mol%)) using the direct doping method. For the first time, the composition of the particles prior to and after embedding them in the glass was analysed using EPMA analysis. Boron was found to be incorporated in already distorted surroundings creating new trapping centers in the particles which are thought to be favourable for the tunnelling process and so for the afterglow at 10K. Despite the partial decomposition of the particles, the glass exhibit afterglow at low temperature confirming to be promising materials for low temperature applications.

The use of stress–strain analysis in structural design or mechanical components is critical for avoiding or investigating structural failures. In the case of complicated designs, mathematical full-field stress modeling produces imprecise predictions. Experimental analysis can be used as a replacement for mathematical modeling, but with the use of currently available strain gauges, it is cumbersome and impossible in the case of moving parts. Mechanoluminescent materials transform mechanical energy into visible light and can be used as a replacement for strain gauges to monitor strain/stress. Three-dimensional printing technology has made major advances in terms of additive manufacturing. In this article, we describe a method to produce an ML 3D print. The fabricated samples are precise and versatile and satisfy the need for easy and non-destructible spatial stress analysis. A 3D printed photopolymer sample with SrAl2O4: Eu, Dy particle addition only to the final layers was tested, and the number of layers was optimized. It was determined that the optimal number of layers for easy detection is in the range of 10 to 20 layers. It opens the possibility for the real-time evaluation of complex uneven forces on complex parts, thus having a good potential for commercialization.

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