Synthesis and luminescent properties of SnO2:Eu nanopowder via polyacrylamide gel method

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Abstract

Nanocrystalline europium-doped tine oxide (SnO2:Eu) were synthesized by a polyacrylamide gel method. The effects of heat treatment on structure, grain size and luminescence properties of SnO2:Eu were studied with X-ray powder diffraction, transmission electron microscopy and photoluminescence measurements. The results indicate that high heat treatments can enhance greatly luminescence intensity of the samples. Furthermore, the presence of carbon network/cages in the polyacrylamide gel can effectively prevent particles agglomeration, so even when sintered at higher temperatures (1000 °C), the grain size is still below 20 nm.

Introduction

Recently, most research interests have been focused on rare-earth (RE) ions-doped semiconductors because of their potential applications in thin-film electroluminescent (TFEL) devices [1], cathodoluminescent devices [2]. Tin oxides (SnO2), with a wide band gap (3.6 eV), is a very important n-type semiconductor. There has been a growing interest in luminescence of RE ions-doped SnO2, such as SnO2:Eu [3], [4], SnO2:Dy [5]. But due to the large difference of the radius and charge between RE ions and Sn4+, it is difficult for RE ions to enter the lattice of SnO2, which results in the poor luminescence of the phosphor.

With a motivation to resolve this problem, many investigations have been done on various synthesis routes of nanosized RE-doped SnO2. Among them, the most common routes involve coprecipitation [3], sol–gel [4], [5] and so forth. In these methods, starting from tin chlorides (SnCl4 or SnCl2) is generally preferred because they are easy to perform and the cost is very low [6], but the chlorine ions are very difficult to remove which can affect inevitably the luminescence of RE-doped SnO2. In our paper, we adopted metal Sn as starting materials to prepare nanosized SnO2:Eu. In this way, the effect of chloride ions can be eliminated. On the other hand, it is well known that the polyacrylamide sol–gel process was a fast, cheap, reproducible and easily scaled up chemical route for obtaining fine powders of composite oxide [7], [8]. During the synthesis process, because the metal ions are completely dissolved in polymeric resin, the PG synthesis provides a molecular level mixing of elements [9], [10], [11], which helps the RE ions to incorporate into SnO2.

In this paper, we will describe the properties of Eu-doped tin oxide nanocrystallines produced by polyacrylamide gel method. The concentration of Eu ions in the samples was kept constant at 1 mol% and this value was checked by chemical analysis. The properties of the powders were characterized and estimated by using X-ray diffraction (XRD), infrared absorption (IR) and photoluminescence (PL).

Section snippets

Synthesis

The procedure used to prepare nanosized SnO2:Eu is as follows. Firstly, 1.206 g of pure Sn (8 mmol) was dissolve in 20 mL cold dilute nitric acid (2 mol L−1). In order to accelerate dissolution of Sn, 3.362 g citric acid (16 mmol) was added. The mixture were kept stirring for 2 h to obtain transparent yellow solutions. The final PH was controlled as 6–7 by using dilute ammonia. Subsequently, the monomers of acrylamide (3 g) and the cross-linker N,N-methylene-bisacrylamide (0.429 g) were added into the

Results and discussions

The XRD patterns of SnO2:Eu sintered at different temperatures between 400 and 1000 °C are shown in Fig. 1. All the reflections are well consistent with JCPDS 41-1445, which confirm the samples as a pure tetragonal rutile crystalline phase of tin oxide and no characteristic peaks of impurities are observed. On the other hand, it is clear to see that the width of the reflections is considerably broadened, indicating that a small crystalline domain size. And the width of the reflections decreases

Conclusions

In this paper, we adopted polyacrylamide gel method to prepare nanosized europium doped tine oxide (SnO2:Eu) successfully. The powders obtained are all below 20 nm with a uniform distribution of the size and shape. The more important is that the as-prepared samples exhibited strong luminescence of Eu3+ under the host excitation, which indicated that energy could transfer efficiently from SnO2 to Eu3+ ions.

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