## 1 Introduction  
Micron-sized inorganic long afterglow luminescent materials are widely used in commercial products due to their excellent afterglow properties. Sustained luminescence is a unique optical process in which the luminescent material continues to emit a long-lasting afterglow after the end of excitation [1; 2; 3] and thus is widely used in security marking and night vision displays [4]. It is due to their excellent optical and afterglow properties that afterglow materials are currently playing an indispensable role in applications such as optical imaging and treatment of tumors [5; 6], information anti-counterfeiting [7; 8; 9] and multiple encryption [10; 11; 12], photocatalysis [13], fingerprinting, bio-imaging [14], photovoltaic sensing [15; 16; 17; 18; 19; 20], and light-emitting diodes [21].  
Inorganic phosphors, especially those doped with rare earths, transition metals, and main group metals, show unique advantages in high stability, long afterglow time, tunable luminescence color (broad band from UV to IR), and high photoluminescence quantum yield (PLQY) due to the unique electronic structure of dopant ions. Since the discovery of long-afterglow luminescence at the beginning of the 20 th century, great progress has been made in the development of long-afterglow materials. They have been rapidly developed in the past decade, and as a result, doped inorganic luminescent materials have been widely reported. Such as the well-known ZnGa\({}_{2}\)O\({}_{4}\):Cr\({}^{3+}\), SrAl\({}_{2}\)O\({}_{4}\):Eu\({}^{2+}\), Dy\({}^{3+}\), Zn\({}_{2}\)GeO\({}_{4}\):Mn\({}^{2+}\), and the newly discovered CsPbBr\({}_{3}\):La\({}^{3+}\)[22; 23; 24; 25]. In addition, more and more persistence has been reported, encouraged by the rapid development of synthesis techniques and precision optical instruments. Significant progress has been made in the exploration of the composition of persistent luminescent materials, persistent luminescent properties, working principles, and modulation methods [26; 27; 28; 29; 30]. Micrometer-scale inorganic long afterglow luminescent materials are even more widely used in commercial products because of their excellent afterglow properties.  
SrAl2O4:Eu2+, Dy3+ is a representative of inorganic long afterglow luminescent materials, first synthesized by [PERSON] in 1996, which has several outstanding advantages: stability, high efficiency, and less toxicity [31]. However, the current production process of commercial SrAl2O4:Eu2+, Dy3+ is based on solid-phase reaction [32; 33; 34; 35; 36; 37], which leads to poor homogeneity and product grain size in the micrometer range, thus limiting the practical application of SrAl2O4:Eu2+, Dy3+ phosphors in fields such as bioimaging, biomedicine, and fine chemicals. However, with the advancement of industrial and medical technologies, there is an urgent need for nanophosphors with good optical properties, uniform particles, and controllable morphology [17; 38].  
In this work, we select low-grade or non-polar alkane solvents to treat commercial SrAl2O4:Eu2+, Dy3+ phosphors by the stirring solvent heat method to maximize the protection of optical and afterglow properties, as well as verify the general applicability of this work. At the same time, a certain amount of sub-micron and nano-sized phosphors with good afterglow properties were prepared and extracted in this work. Compared with other top-down techniques such as mechanical milling, wet milling, laser ablation, etc., this work was easy to operate, the product still maintains good optical properties, and it can be simply dispersed without agglomeration, which is conducive to practical applications. In addition, the reaction solvent can be recycled after the reaction, which is not only resource-saving but also environmentally friendly, in line with the theme of green chemistry nowadays.