Non‐Rare‐Earth UVC Persistent Phosphors Enabled by Bismuth Doping

Abstract

Among various energy storage materials, long persistent phosphors (LPPs) are a class of "optical battery" that can emit luminescence continuously for a long time after the removal of excitation sources. [6] Since the report of greenemitting SrAl 2 O 4 :Eu 2+ , Dy 3+ LPPs in 1996, [7] a large variety of LPPs have been rapidly developed and widely used in security signs, displays and in vivo biological imaging, to name just a few. [8][9][10][11][12][13][14][15] Among these phosphors, representative ones with excellent afterglow properties are CaAl 2 O 4 :Eu 2+ , Nd 3+ , [16] Y 2 O 2 S:Eu 3+ , Mg 2+ , Ti 4+ , [17] and Zn 3 Ga 2 Ge 2 O 10 :Cr 3+ , [18] which emit in the visible and near-infrared spectral regions. [19][20][21][22][23] In marked contrast, the research and development of UVC LPPs relatively lag behind, although such phosphors hold great potential in terms of sterilization, drug release, and cancer therapy. [24][25][26] To date, only a handful of UVC LPPs have been successfully developed, and all of them involve the use of rare-earth (RE) ion, Pr 3+ , as the UVC emitter. [25,[27][28][29] Given that REs are expensive due to the limited abundance in the earth and great imbalance between supply and demand, it is imperative to explore and develop non-REenabled UVC LPPs, which may not only enrich the bank of LPPs, but also offer new opportunities for rationally designing non-RE-activated phosphors.The ingredients for designing LPPs involve the choice of suitable emitters, hosts, and traps for either electrons or holes. The emission wavelength of LPPs is governed by the emitter [30] and the afterglow duration and intensity depend on the species and concentrations of traps with suitable depths; [31] in most cases structural defects can be employed as charge carrier traps. [6] As a result, to obtain a non-RE UVC persistent phosphor, using a non-RE luminescence center that can emit UVC light and choosing a suitable matrix with appropriate defects must be satisfied simultaneously. Bismuth, with the electronic configuration of [Xe] 4f 14 5d 10 6s 2 6p 3 , is one of the most investigated main-group elements, which has been known as nearly fullspectrum luminescence ions due to the existence of multiple oxidation states and the propensity for the formation of clusters. [32][33][34][35][36] In recent years, Bi 3+ -doped LPPs have received wideranging attention and been considered as potential alternatives to RE-doped cousins. [37][38][39][40] For instance, previous works revealed that Bi 3+ -doped LiYGeO 4 and LiScGeO 4 show ultraviolet-A afterglow, [37,38] Bi 3+ -doped KGaGeO 4 and CaGa 2 O 4 show blue and Long persistent phosphors (LPPs) have drawn tremendous research interest owing to their mysterious optical phenomena and widespread applications. LPPs in the ultraviolet-C (UVC, 200-280 nm) spectral range particularly hold promise in terms of sterilization, drug release, and cancer therapy. However, all reported UVC LPPs have so far relied on the use of Pr 3+ as the emitter, resulting in a limited scope of such phos...

Exploring Intrinsic Electron-Trapping Centers for Persistent Luminescence in Bi3+-Doped LiREGeO4 (RE = Y, Sc, Lu): Mechanistic Origin from First-Principles Calculations

“…The thermodynamic charge-transition levels (or defect levels) within the band gap correspond to the Fermi level position at which a transition occurs from one charge state ( q ) to another ( q ′). The level position ε­( q / q ′) with reference to the host VBM can be calculated by , where Δ E f ( q or q ′; E F = 0) is the formation energy of the defect in charge state q or q ′ when the Fermi level is set at 0 eV.…”

“…The thermodynamic charge-transition levels (or defect levels) within the band gap correspond to the Fermi level position at which a transition occurs from one charge state (q) to another (q′). The level position ε(q/ q′) with reference to the host VBM can be calculated by 29,30…”

Controlling X-ray-activated persistent luminescence for emerging applications

“…The X-PersL wavelength was further shortened to around 231 nm by the same group through the theory-guided defect tuning strategy in LaPO 4 : Pr 3+ phosphors [46]. In another development, the main-group Bi 3+ ion was selected as the UVC emitter for X-PersL, which exhibited narrow afterglow peaking at 240 nm for over 2 h after ceasing X-ray irradiation [47]. These investigations create a research hotspot of high-energy UVC PersL, opening up new applications in sterilization, drug release, and cancer therapy [14,48].…”

“…After postsynthetic treatment using CaH 2 as oxygen getters, the initial intensity and duration of PersL were both improved due to the increased concentration of deep traps associated with oxygen divacancies in [PO 4 ], which was confirmed by positron annihilation lifetime spectroscopy and electron spin resonance measurements. In a subsequent study, the theoretical method was further employed to tune the intrinsic defects in YPO 4 :Bi 3+ by varying the reactant ratio, which identifies Y vacancies and Y-O vacancy complexes as the hole traps for UVC X-PersL [47].…”

Design of a defect‐induced orange persistent luminescence phosphor BaZnGeO4:Bi3+

“…Bi 3+ can exhibit blue to red emission with the wavelength of 400-700 nm in an appropriate matrix. [14][15][16] BaZnGeO 4 crystallizes in the hexagonal system with a stuffed structure derived from the high-tridymite framework. The space group is P6 3 .…”