Research Progress Of Red Long Afterglow Materials

Long afterglow materials have attractive application prospects. However, compared with the blue and green long persistence materials, the initial strength and decay time of red long afterglow materials cannot satisfy the practical application. Therefore, it is extremely urgent to explore efficient red long afterglow materials. Thus, it is of great theoretical and practical significance to explore and study new red long afterglow materials. In this review, we summarize the red afterglow performance and application of the long persistence materials, discusses the existing problems, and puts forward some suggestions for development of red long persistence materials.Luminescent materials can store energy after absorbing light energy, radiant energy, electrical energy, mechanical energy and other external energy. And then release the stored energy in the form of light after the excitation is stopped, and the luminescence can last for a long time (from a few seconds to dozens of hours). This luminescence is called long afterglow and the materials with long afterglow properties are called long afterglow materials. Currently, it is known that the mechanism of luminescence is a form of thermal excitation, results from storage of the excitation energy in traps and subsequent release induced by external thermal energy.The long afterglow phenomenon has been found in nature materials for over 1000 years, for example, documented in ancient Chinese paintings. The first scientifically documented long afterglow material was the bologna stone discovered by Vincenzo Cascariolo in 1602, but it was not until 1640 that Fortunius Liceyus recorded its luminous principle. The afterglow is generated by the electron transition of Cu+ impurity level, and the Cu2+ is reduced to the sulfur vacancy generated by Cu+ as the trap center to store energy. Since then, there is a lot of long persistence materials have been reported, but it was only in 1996 that long persistence materials became a new optical materials research hotspot due to the discovery of the excellent SrAl2O4:Eu2+,Dy3+ by Matsuzawa. And thousands of papers about LLP and its applications were published, including emergency lighting, optical storage, biology, drug carrier, solar cells, anti-counterfeiting, photocatalytic and biological imaging, etc.Red is one of the three primary colors, its long persistence materials can be widely used in fluorescent color display device, temperature senor, emergency warning and so on. However, so far, compared with blue (CaAl2O4:Eu2+,Nd3+) and green (SrAl2O4:Eu2+,Dy3+) long persistence materials, the initial strength and attenuation time of red long afterglow materials are far from meeting the needs of practical application. Therefore, it is extremely urgent to explore efficient red long afterglow materials. What's more, it is necessary for us to continue the development of new LPL phosphor for better understanding of the LPL mechanism.In long persistence luminous, emitters and traps as two kinds of active centers are involved. Emitters are the centers capable of luminous emission after being excited. The emitters mainly determine the emission wavelength of LPL phosphors. Trap is often no radiation, but store excitation and releases it gradually to the emitters due to thermal stimulation or other physical stimulation. And the nature of traps determines the strength and time of long afterglow materials (e.g., type, depth and distribution of traps). The paper mainly reviews the progress of afterglow mechanism, synthesis technology, type and application of emission centers.