Effect of Bi3+ incoporation on up/downconversion luminescence and photocatalytic activity of Gd2O3

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Highlights

  • The Bi3+ doped gadolinium oxide phosphors were synthesized by co-precipitation and the influence of Bi3+ concentrations on the luminescence properties were studied.

  • The photocatalysis technology based on semiconductors could degrade pollutants under visible light, and is considered as a promising method to deal with the organic pollutants.

  • The luminescence and photocatalysis properties were systematically studied by emission spectra and evaluating the degradation of RhB respectively. Moreover, products were characterized with XRD, FESEM, TEM, UV–vis and BET respectively.

Abstract

Gd2O3 has been selected as host material for optical studies due to its good chemical, photothermal, and photochemical stabilities. A series of (Gd1-xBix)2O3 (x = 0.03, 0.05, 0.1, 0.2, 0.3, 0.5) samples were obtained via coprecipitation method. The samples were characterized by X-ray powder diffractometry (XRD), transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED), BET surface area method, UV-visible (UV–vis) absorption spectra and photoluminescence (PL) spectroscopy. The crystalline-to-amorphous phase transformation was found with higher concentration of Bi3+ incorporation. The dependence of Bi3+ concentration on the upconversion/downconversion luminescence intensity were investigated and the photocatalytic activity of the synthesized samples was also evaluated by the degradation of Rhodamine B (RhB) dye in aqueous solution under visible light irradiations. The samples (Gd0.5Bi0.5)2O3 exhibited better photocatalytic activity for RhB degradation than Gd2O3 and Bi2O3 due to phase transformation, modified band structures and higher surface area.

Graphical abstract

A series of (Gd1-xBix)2O3 (x = 0.03, 0.05, 0.1, 0.2, 0.3, 0.5) samples were obtained via coprecipitation method. The dependence of Bi3+ concentration on the upconversion/ downconversion luminescence intensity were investigated. The photocatalytic activity of the synthesized samples was also evaluated by the degradation of Rhodamine B (RhB) dye in aqueous solution under visible light irradiations.

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Introduction

The rising energy consumption and environmental pollution in recent decades have raised the demand for clean and sustainable energy such as solar energy [1], [2], [3]. Photocatalyst, as a semiconductor, has attracted much attention due to its potential applications such as hydrogen evolution and removal of the organic pollutants in the environment [4]. It can be a certain wavelength range of solar energy into other forms of energy [5], [6], [7]. However, the photocatalysts still have some problems, such as only able to absorb ultraviolet light and part of visible light because of large band gap and high carrier separation efficiency. To develop new photocatalysts active under visible light, various efforts have been made so far.

Bi3+ ions with 6 s2 electronic configuration [8] can function as both an activator and a sensitizer for luminescent materials. Emission of Bi3+ usually originates from its 3P11S0 transition. The position and the splitting of the emitting level 3P1 are sensitive to the local crystal field of Bi3+ ions [9], which results in the band profile and peak wavelength of Bi3+ emission varying apparently in different host matrices. Especially, there are numerous studies focused on containing Bi3+ ion compounds to enhance photocatalytic performance, such as Bi/BiOBr0.5Cl0.5 [10], Bi2MoO6 [11], Bi@BiOx(OH)y [12], BiOCl [13], Bi19Br3S27 [14], Bi3.64Mo0.36O6.55 [15] and Bi2O3 [16].

In the past several years, gadolinium oxide (Gd2O3) was considered to a commendable host matrix material because of its good chemical durability [17], thermal stability [18], large bandgap (5.4 eV) and low phonon energy (phonon cutoff ≈ 600 cm−1) [19]. In upconversion, Gd2O3 would increase the possibility of radiative transitions and in turn result in a high quantum yield of upconversion process [20], [21], [22]. In addition, Gd2O3 can be easily doped with metal ions, which means high concentration doping is possible [23,24].

At present, there are some reports on Bi3+-doped Gd2O3 photocatalysts [25,26] and phosphors [27,28], the relation between photocatalytic activity and photoluminescence, and the improvement of photocatalysis by rare earth ion doping are still not clear. In this work, a series of (Gd1-x Bix)2O3 (x = 0.03, 0.05, 0.1, 0.2, 0.3, 0.5) were prepared by coprecipitation method. The effects of Bi3+ ion concentration on the crystal structure, luminescence properties and the photocatalytic behavior of Gd2O3 were studied. Mechanism of the enhanced photocatalytic activity were also discussed in this work.

Section snippets

Experimental procedure

The phosphors were prepared by co-precipitation technique. High purity Gd2O3 (99.99%) and Bi2O3 (99.99%, 0–50.0 mol%) were precisely weighted and mixed with 25 ml nitric acid and diluted by 20 ml deionized water to get the co-nitrates of gadolinium and bismuth ((Gd,Bi)3NO3). Then solution was mixed with a lithium hydroxide solution in order to neutralize the nitric acid and form a precipitate. After rinsing with deionized water and alcohol three times respectively and drying at 80 °C for 24 h,

Results and discussion

XRD patterns of these (Gd1-xBix)2O3 phosphors prepared by different Bi3+ concentration are shown in Fig. 1(a) in comparison with the standard peak positions of the Gd2O3 hexagonal phase (JCPDS card no. 12–0797), and the space group is P3m1. When the concentration ratio x = 0.03, 0.05, the diffraction peak position is consistent with the standard card, no distinguished secondary phases were identified. However, with the increase of concentration, when x = 0.1, 0.2 and 0.3, the diffraction

Conclusions

(Gd1-xBix)2O3 exhibited up-down-conversion luminescence and excellent photocatalytic activity for RhB degradation under the visible light irradiation. RhB levels were degraded to 15%, 80% by using Gd2O3 and (Gd0.5Bi0.5)2O3, respectively, while the photocatalytic activity was increased by 5.3 times. The improved photocatalytic performance may be attributed to enlarged photo-response, the low carrier recombination rate and large interfacial surface area. This is mainly due to the up-conversion of

CRediT authorship contribution statement

Xuquan Wang: Data curation, Writing – original draft. Fei Wang: Writing – review & editing, Conceptualization, Methodology, Software. Baoqiang Xu: Visualization, Investigation. Bin Yang: Supervision.

Declaration of Competing Interest

The authors declared that they have no conflicts of interest to this work.

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgments

The work is financially supported by Top Young Talents of Yunnan Province Ten Thousand Talents Plan (109720190004) and Yunnan Fundamental Research Projects-General Project (202101AT070555). Thanks to Mr. Ju Haidong from Kunming University for the up-conversion luminescence test.

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