Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Preparation, characterization, and luminescence properties of BiLaWO6:Eu3+ red-emitting phosphors for w-LEDs
Graphical abstract
A novel BiLaWO6:Eu3+ phosphor shows red emission at 617 nm under the 467 nm wavelength excitation and a high color purity at 99.2%.
Introduction
In recent decades, white light-emitting diodes (w-LEDs) have attracted considerable attention. W-LEDs are considered the new generation of solid-state lighting because of their many advantages, such as fine light stability, high efficiency, eco-friendly and energy-saving characteristics, and long lifetime [[1], [2], [3], [4], [5]]. Commercial w-LEDs have been produced by InGaN blue LED combined with the yellow-emitting phosphor Y3Al5O12:Ce3+. However, many studies have reported that the types of w-LEDs show high color temperature and low color rendering index (CRI), due to the lack of red color [[6], [7], [8], [9]]. Therefore, the development of novel red-emitting materials with improved color purity and good absorption is increasingly desirable.
At present, a number of rare-earth tungstates, such as Ba6GdW3O18:Eu3+ [10], NaLaMgWO6:Pr3+ [11], LaBWO6:Tb3+,Eu3+ [12], RE2(WO4)3:Eu3+ [13], and BaWO4:Eu3+ [14], are regarded as promising candidates for photoluminescent materials owing to their optical properties and excellent thermal and chemical stability. In 2012, Bi2MO6 (M = W, Mo):Eu3+ nanometer materials were prepared by the hydrothermal method and applied in fluorescent marking [15]. In 2013, Zhang et al. discovered the BiErWO6 photocatalyst with novel infrared responsive property [16]. In 2016, BiYWO6 was synthesized by low-temperature routes and is now regarded as a promising visible light-activated photocatalyst [4]. In 2018, Pradeep P. Shanbogh et al. found the BiTbWO6 compound with better photocatalytic activity than BiEuWO6 [17]. The BiLaWO6 compound belongs to the Aurivillius family of layered perovskites. The compound is also a variant of Bi2-xLnxWO6, where x is often between 0.3 and 1.3 and Ln is a lanthanide-series element [18]. The Eu3+ ion is an important activator in many studies not only because it has an efficient and relatively narrow band but also because it is sensitive to the change in lattice conditions [19]. Thus, it has been widely used in commercialized red phosphors [[20], [21], [22]].
To date, we have not found any reports of Eu3+-doped bismuth lanthanum tungstate BiLaWO6 red-emitting phosphors. Here, the red-emitting phosphor BiLa1-xEuxWO6 (x = 0.02–0.70) was successfully synthesized, and the features of crystal structure and photoluminescence (PL) were studied in detail.
Section snippets
Experimental procedure
BiLaWO6 doped with Eu3+ ion powders (x = 0.02, 0.05, 0.10, 0.30, 0.50, 0.60, and 0.70) were prepared by the conventional solid-state reaction. The resultant phosphors were denoted as BLWO:xEu3+, where x is the molar ratio of Eu2O3 to La2O3 in the starting materials. Stoichiometric amounts of La2O3 (99.99%), Bi2O3 (A.R.), WO3 (A.R.), and Eu2O3 (99.99%) were sufficiently blended and introduced into a muffle furnace and then sintered at 1273 K for 3 h. The chemical reaction in the furnace at high
Results and discussion
XRD patterns of all the BLWO:xEu3+ samples were studied at various concentrations (x = 0.02, 0.05, 0.10, 0.30, 0.50, 0.60, and 0.70) to check the phase purity. Fig. 1(a) shows that all diffraction peak positions coincide well with the standard card BiLaWO6 (JCPDS 33-0203). The results indicate that all BLWO:xEu3+ samples are single phase and have the same crystal structure as pure LaBiWO6. Furthermore, Eu3+ ions successfully substitute the La3+ in the host lattice considering that the ionic radii
Conclusions
Eu3+-doped BLWO samples as novel red phosphors were efficiently prepared by the facile solid-state reaction technique. Primary XRD analysis of the crystallites showed single-phase formation. The Rietveld refined analysis confirmed that Eu3+ ions entered the crystal lattice. The strongest excitation and emission peaks were found at 467 and 617 nm for the phosphor, respectively. The optimal concentration of Eu3+ doping was obtained as approximately 50 mol%. PL spectra under different temperatures
Acknowledgments
The work was supported by the National Natural Science Foundation of China (Grant no. 31572038), the Fundamental Research Funds for the Central Universities (2452019076), Hunan Provincial Key Laboratory of Xiangnan Rare-Precious Metals Compounds and Applications (2019XGJSKFJJ01), the Construct Program of the Key Discipline in Hunan Province, the Projects of the Education Department of Hunan Province (No. 18A465), and Science and Technology Plan Project of Chenzhou City (jsyf2017014).
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