Preparing and testing the reliability of long-afterglow SrAl2O4:Eu2+, Dy3+ phosphor flexible films for temperature sensing

Abstract

Owing to its stability and environment-friendly properties, the SrAl₂O₄:Eu²⁺, Dy³⁺ (SAOED) phosphor has attracted major scientific interest. With various applications, such as in emergency signage, luminous paints, and traffic signs, it can have a considerable impact on everyday activities. However, SrAl₂O₄ easily undergoes hydrolysis in the presence of atmospheric moisture. To remedy this, we prepared a phosphor film by spin coating to improve its water resistance. The SAOED was coated with epoxy resin glue without destroying the SrAl₂O₄ crystals. A series of reliability tests were conducted on the phosphor films and bare phosphors: high-temperature and high-humidity (HT) tests, thermal-cycling (TC) tests, and xenon lamp aging (XLG) tests. Then, the crystal phase, surface morphology, photoluminescence (PL), afterglow decay, and temperature-dependent PL were analyzed. The X-ray diffraction patterns show that the hydrolysis reaction of SAOED occurred easily, with the SrAl₂O₄ phase becoming the Sr₃Al₂ (OH)₁₂ phase and SrAl₃O₅(OH) generated under HT tests. The PL intensity of the thin film of SAOED decreased 57.2%, 79.3%, and 98.8% after HT tests, XLG tests for 168 h, and TC tests with 10 repetitions from 233 K to 423 K, respectively. Moreover, the afterglow decay time of the SAOED phosphor film was longer than that of bare phosphors. The developed flexible films are excellent candidates for temperature sensing because they exhibit temperature-dependent PL intensity and are highly sensitive to surrounding temperature variation 300–420 K. Thus, SAOED films with stable luminescent signals can be used in energy-efficient, long-lasting temperature-sensing devices, which, apart from being environment-friendly, play a role in improving public safety infrastructure.