Achieving Ultraviolet C and Ultraviolet B Dual‐Band Persistent Luminescence by Manipulating the Garnet Structure

Abstract

PersL is a unique phenomenon that a material emits for an appreciable time (seconds, minutes, hours, or days) after switching off an optical excitation. Without the requirement of a continuous optical excitation, persistent phosphors in the visible and infrared ranges have been extensively studied during past decades and have shown a vast range of promising applications underlying the "persistence" feature, including night-vision displays, [22] bio-imaging, [23,24] and optical information storage. [25] Not until recently have UVC persistent phosphors been found with promising applications in optical communication for all lighting conditions for the first time, with Pr 3+ as the UVC PersL ion. [26] Due to the complete absence of UVC solar radiation in the lower atmosphere, UVC PersL can be visualized free of any disturbance from outdoor lighting or artificial lights. Thus, UVC PersL from phosphors can satisfy a pointing and tracking function independent of ambient lighting conditions. Additionally, persistent photocatalysis, [27] persistent sterilization, [28] self-sustained imaging technique, [26] and other UV-sensitive or UV-stimulated applications [29,30] will be possibly achieved. These promising applications are beyond the expectations from phosphors with visible or infrared PersL.However, the development of UVC and UVB persistent phosphors is encumbered by the foreseeable difficulties. First, selecting an appropriate luminescence ion emitting at UVC and UVB spectral range is required. Pr 3+ is a well-suited luminescence ion with a UV-emissive 4f5d energy level for this purpose. [26] Based on that, UVC and UVB PersL can be achieved within a crystal host only with effective trapping centers to form UV-trapping energy levels. Unfortunately, the exact characteristics of trapping centers remains unclear even for many visible and infrared persistent phosphors using popular host materials such as aluminates, [31,32] gallates, [22][23][24] garnets, [33] and others. [25,34,35] The creation of traps in these phosphors may be varied from lanthanide codoping, [31] Li + doping, [36] and cationic substitution. [22,33] Garnet is a crystal structure in a generic chemical formula {A} 3 [B] 2 (C) 3 O 12 , consisting of linked [AO 8 ], [BO 6 ], and [CO 4 ] polyhedra. It is one of the most studied host matrixes accommodating lanthanide ions or transition metal ions due to its chemical and physical stability and tolerant nature for cationic substitution. [37][38][39][40] Cationic substitution or heterovalent cosubstitution at its A, B, and/or C Persistent luminescence (PersL) at the high-energy spectral end (ultraviolet, UV) is generally hard to achieve, although a long-lasting UV PersL can play an irreplaceable role in outdoor imaging and other UV-triggered applications. No PersL with dual ultraviolet C (UVC) and ultraviolet B (UVB) bands from a single material has previously been attained until the authors have designed Pr 3+ -doped (Ca 1.5 Y 1.5 )(Al 3.5 Si 1.5 )O 12 (CYAS-Pr) through cosubstituting Ca 2+ -Si 4+ into Y 3 Al 5...

Deep-Ultraviolet Emitter: Rare-Earth-Free ZnAl2O4Nanofibers via a Simple Wet Chemical Route

“…The interest toward deep-ultraviolet (UV) phosphors has recently tremendously grown in view of their potential utilization in tri-band-based light-emitting diodes (LEDs) for biochemical and medical applications. − In particular, these materials can be used as so-called C, B, or A UV emission devices for catalyst and sterilization, whereas it has been shown that the sources operating in the C-UV range of 280–200 nm are preferred due to the most efficient germicidal effect. ,− Although rare-earth dopants in phosphors are the most widely used by now, the depletion of natural resources has driven the research efforts to the development of rare-earth-free substitutes suitable for emerging applications. These application needs have risen the issue of suitable materials.…”

Mn2+-Activated Afterglow in a Transparent Perovskite Crystal

“…The past few decades have witnessed the rapid development of the long afterglow materials in both scientific research and industrial commercialization. − In specific, the emergence of the SrAl 2 O 4 :Eu 2+ ,Dy 3+ phosphor has significantly improved both the intensity and duration of afterglow, leading to a successful application in many areas . In this case, Dy 3+ and Eu 2+ ions were codoped in a lattice and acted as a trap center and an emitting activator, respectively, which later inspired many afterglow works. − Since then, codoping of two or more ionic species has become a major strategy for phosphor exploration.…”

Recent advances in Pr3+-activated persistent phosphors

“…To our best knowledge, only a few persistent phosphors have been reported emitting in the UV range, including UVA (320-400 nm) PersL activated by Bi 3+ , [114][115][116][117][118][119][120][121][122] Pb 2+ , 9 or Tb 3+ , 123 UVB (280-320 nm) PersL activated by Pr 3+ 124,125 or Gd 3+ 126-129 and UVC PersL activated by Pr 3+ 40,41,129-131 or Bi 3+ 129,132 and dual-band UVC and UVB PersL activated by Pr 3+ . 53,133 Due to the high 4f5d energy state (the first case in Fig. 2a), Pr 3+ possibly absorbs ultraviolet irradiation via an allowed electric-dipole 4f 2 -4f5d inter-configurational transition.…”

“…Moreover, we recently demonstrated that Pr 3+ can be doped into the modified garnet crystal structure to achieve the UVC and UVB dual-band emission and PersL emission. 133,135 In the Pr 3+ -activated (Ca 1.5 Y 1.5 )(Al 3.5 Si 1.5 )O 12 , the PersL of Pr 3+ is not only at 266 nm but also at 313 nm, and both decays last for B12 h. The solar-blind imaging experiments assisted by this phosphor are discussed and other applications based on the dual-band UVC and UVB PersL capabilities are envisioned. As far as we know, it is the first reported dual-band UVC and UVB persistent phosphor.…”

“…The dual-band UVC and UVB PersL realized in the Pr 3+ doped modified garnet structure shows the hints that cationsize and valence-state mismatch are critical factors for designing UV persistent phosphors. 133 The effective trapping centers needed for UV PersL from Pr 3+ can be manipulated by cationic substitutions under this principal (for example, Ca 2+ -Y 3+ and Si 4+ -Al 3+ in the garnet).…”