Contents lists available at ScienceDirect Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin Nanothick aluminate long-afterglow phosphors using inherited hydrothermal deriving Chen-Yu Wu a , Chien-Ming Lei b , Rudder Wu c , Toshiaki Takei d , Chau-Chang Chou e , Shing-Hoa Wang e , Horng-Yi Chang a, ⁎ a Department of Marine Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan, ROC b Department of Chemical & Materials Engineering and Graduate Institute of Nanomaterials, Chinese Culture University, Taipei 11114, Taiwan, ROC c Research Center for Structural Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan d International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan e Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan, ROC ARTICLE INFO Keywords: Aluminate Inherited hydrothermal Phosphor Afterglow ABSTRACT A novel strategy of the inherited hydrothermal method was used to prepare SrAl 2 O 4 : 0.01Eu 2+ , 0.01Dy 3+ (SAO) without boron (ISAO) and boron-doping (BSAO) via NaAlO 2 as an aluminum source and mineralizer at 200 °C for 6–24 h. The investigated optical properties was correlated to phase transformation and phosphor morphology. The main constituting phases of Al 2 (OOH) 2 and SrCO 3 transformed to monoclinic SrAl 4 O 7 and mixed mono- clinic/hexagonal SrAl 2 O 4 then pure monoclinic SrAl 2 O 4 during different hydrothermal period. The hydro- thermally prepared samples exhibited flower-like morphology. The annealed plate phosphors with nanothick single crystals inherited from hydrothermal feature. The shift of photoluminescence (PL) peak wavelength corresponded to the phase transformation from SrAl 4 O 7 to SrAl 2 O 4 with hydrothermal time for ISAO and BSAO. The PL intensity increased with hydrothermal time due to achieving the pure SrAl 2 O 4 phase with preferred orientation geometry and further enhanced by boron-doping. The afterglow of BSAO was significantly enhanced than ISAO, solid-state prepared MSAO and commercial SAO at the initial 100 s after excitation cut-off. The boron doped in the BSAO was scarcely on the grain surface as to small grain size. Thus, the afterglow enhancement should be attributed to the boron in the lattice inducing defect traps. Overall, the inherited hydrothermal and boron-doping derived nanothick SAOs with large surface preferred orientation enhanced the PL and afterglow properties. 1. Introduction Long-afterglow phosphor of doped strontium aluminate (SrAl 2 O 4 : Eu 2+ , Dy 3+ ) is widely applied in several fields of energy-saving and safety installations [1–5]. Aluminates have several superior properties such as high photoluminescence (PL) intensity, color purity, longer afterglow, chemical stability, safety, and no radioactivity compared to classical sulfide phosphorescent phosphors [6]. Spinel SrAl 2 O 4 [7] has a distorted stuffed tridymite structure, in which the crystal framework consists of layers formed from tetrahedral AlO 4 linked to form trigon- ally distorted rings. These layers are stacked and connected by the tetrahedral apices, constructing a three-dimensional structure with open channels, which are occupied by Sr 2+ ions [8,9]. SrAl 2 O 4 exhibits polymorphism from monoclinic to hexagonal structure at 650–680 °C reversibly [9,10]. The monoclinic form of SrAl 2 O 4 contains two different sites available for Sr 2+ ions in the opened channels; both the sites of Sr1 and Sr2, coordinated by nine oxygen ions, are present in equal amounts in the lattice [11]. Europium ions, Eu 2+ , can substitute the Sr 2+ ions, as their ionic radii are similar (1.30 Å and 1.31 Å, re- spectively) [12]. Thus, the europium ions subjected to two different chemical environments at both the Sr sites result in emission with dif- ferent spectra: one emits in the blue spectral range only at low tem- peratures and the other in the green spectral range [13]. The photoluminescence (PL) and afterglow of doped SrAl 2 O 4 phosphors are not only affected by the particle size, crystal size, and geometric structure, but also by the introduction of co-dopants such as Eu, Dy, and B elements [4,14–17]. The afterglow characteristics of doped SrAl 2 O 4 phosphors were explained in terms of trapping and thermal release of charge carriers at various temperatures, wherein Eu is an emitter and Dy serves as a trapping center. The addition of Dy 3+ https://doi.org/10.1016/j.jlumin.2018.10.004 Received 8 May 2018; Received in revised form 24 September 2018; Accepted 7 October 2018 ⁎ Correspondence to: Department of Marine Engineering, National Taiwan Ocean University, 2, Pei-Ning Rd., Keelung 20224, Taiwan, ROC. E-mail address: hychang@mail.ntou.edu.tw (H.-Y. Chang). Journal of Luminescence 206 (2019) 593–602 Available online 13 October 2018 0022-2313/ © 2018 Elsevier B.V. All rights reserved. T