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Dual-Mode Luminescence Modulation upon Visible-Light-Driven Photochromism with High Contrast for Inorganic Luminescence Ferroelectrics Qiwei Zhang,† Xuewen Zheng,† Haiqin Sun,† Wenqing Li,† Xusheng Wang,‡ Xihong Hao,*,† and Shengli An† †
School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, 7 Arerding Street, Kun District, Baotou 014010, People’s Republic of China ‡ Functional Materials Research Laboratory, School of Materials Science and Engineering, Tongji University, 4800 Caoyang Road, Shanghai 201804, People’s Republic of China S Supporting Information *
ABSTRACT: A luminescence ferroelectric oxide, Na0.5Bi2.5Nb2O9 (NBN), system with bismuth layer structure introduced by lanthanide ion (Er3+) has been demonstrated to exhibit reversible, high-contrast luminescence modulation (95%) and excellent fatigue resistance based on visible-light-driven photochromism (407 nm or sunlight). The coloration and decoloration process can be effectively read out by dual modes, upconversion and downshifting, and reversibly converted between green and dark gray by alternating visible light or sunlight irradiation and thermal stimulus. The luminescence modulation degree upon photochromic reactions is strongly dependent upon irradiation light wavelength and irradiation time. After undergoing several cycles, there are no significant degradations, showing high reversibility. Considering its high-contrast photoswitchable luminescence feature and intrinsic ferroelectricity of NBN host, NBN-based multifunctional materials can be suggested as a promising candidate for new potentials in photonic storage and optoelectronic multifunctional devices. KEYWORDS: ferroelectric oxide, luminescence modulation, fatigue resistance, photochromism, reversibility, photonic storage
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materials exhibit sensitivity to ultraviolet (UV) light,11−13 with only a few sensitive to visible light, and they usually exhibit poor reversibility (e.g., difficultly being photocolored once for thermal bleached WO3 or MoO3) and low fatigability; it is difficult to efficiently use most commercially available laser sources and solar energy. Therefore, developing new PC materials with visible light sensitivity still remains a critical challenge to their practical applications. We recently reported the PC behavior of bismuth layer structure ferroelectrics [Na0.5Bi2.5Nb2O9 (NBN)] and introduced Eu or Pr ions into the NBN host to realize reversible luminescence modulation upon PC reactions.14,15 We believe that the combination of luminescence, PC, and ferroelectrics may lead to future multifunctional optoelectronic applications.16−18 This may open up new avenues for the discovery of a new series of functionalized materials capable of modulating the luminescence emission through incorporation of different dopants (activators and sensitizers) and a suitable host with the bismuth layer structure of general formula (Bi2O2)2+(An − 1BnO3n + 1)2, where A is a mono-, di-, or trivalent element, B is some highly
INTRODUCTION In recent years, inorganic photochromic compounds changing their color upon light irradiation have attracted considerable attention, have shown great promise in optical data storage, switches, and optoelectronic devices, and have been extensively investigated.1−3 They have been demonstrated to display some advantages over organic counterparts: better thermal stability, strength, chemical resistance, and macroscopic shape molding (thin films, coatings, etc.).4,5 Although the research on them is well-known, such as transition metal oxides (WO3, MoO3, TiO2, and V2O5), polyoxometalates, alkali metal azides, sodalite, and the related hybrid materials, most studies are mainly focused on the phenomenon of photochromism (PC),6,7 while studies on their luminescence modulation upon PC reactions are extremely rare,8 in particular on reversible photoswitching behavior. The photoswitching of luminescence is particularly valuable for optical storage and is considered to be one of the most attractive concepts for the realization of a nondestructive optical readout among several methods or ideas, such as refractive index, electric conductance, magnetic interactions, etc.9,10 Thus far, limited success has been made in switching the luminescence with high luminescence contrast and excellent reproducibility of inorganic materials because of insufficient conversion or irreversible reactions. In addition, most of the reported inorganic PC © 2016 American Chemical Society
Received: December 15, 2015 Accepted: January 28, 2016 Published: January 28, 2016 4789
DOI: 10.1021/acsami.5b12262 ACS Appl. Mater. Interfaces 2016, 8, 4789−4794
ACS Applied Materials & Interfaces
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RESULTS AND DISCUSSION XRD patterns of various amounts of Er2O3-doped NBN samples (NBN:xEr, where x = 0, 0.01, 0.02, 0.04, 0.06, and 0.08) are shown in Figure 2a. The main phase of NBN [Joint Committee
charged cation, and n is the number of octahedral layers in perovskite layers.19 Despite the reversible luminescence photoswitching upon photochromic reactions in the NBN system, there is still a roadblock toward practical applications: low luminescent emission contrast (
