Hydrothermal synthesis of YBO3:Tb3+ microflowers and their luminescence properties

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Abstract

Three-dimensional flowerlike YBO3:Tb3+ phosphors have been successfully prepared by an efficient surfactant-free hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDS) spectrometry, selected area electron diffraction (SAED), photoluminescence (PL) spectra were used to characterize the samples. The as-obtained samples present flowerlike agglomerates composed of nanoflakes with thickness of 20 nm and high crystallinity in spite of the moderate reaction temperature of 180 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. The different luminescent intensity with different molar ratio of Y–Tb [Y:Tb = 8:2; 7:3; 6:4; 5:5; 4:6], YBO3:Tb3+ phosphors exhibit different light (white, red, green) under ultraviolet excitation, which might find potential applications in the fields such as light display systems and optoelectronic devices.

Research highlights

▶ We report an efficient surfactant-free hydrothermal approach to synthesize hexagonal YBO3:Tb3+ with novel self-assembled 3D architectures. The as-obtained samples present flowerlike agglomerates composed of nanoflakes with thickness of 20 nm and high crystallinity in 180 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. The luminescent properties of the flowerlike YBO3:Tb3+ composed of nanoflakes have also been reported and investigated.

Introduction

Recently, orthoborate phosphors are widely used in field-emission displays (FEDs), plasma display panels (PDPs), cathode ray tubes (CRTs) and a new generation of Hg-free fluorescent lamps [1], [2]. Among the orthoborate phosphors, YBO3-based phosphors have attracted much attention due to their low toxicity, strong luminescence intensity, high chemical stability, and exceptional optical damage threshold [3], [4], [5]. YBO3:Tb3+ phosphor is regarded as one of the potential green phosphors to be utilized in PDPs [6]. It has a strong absorption band in the vacuum ultraviolet (VUV) range, and its luminance under VUV excitation is as high as conventional commercial green phosphors. Therefore, research on preparation and luminescence property of YBO3:Tb3+ phosphor is of great importance.

YBO3:Tb3+ phosphor has been synthesized via various routes, such as solid-state reaction [7], sol–gel method [1], [8], spray pyrolysis method [9] and hydrothermal method [10]. Compared to the other routes, the hydrothermal method is a promising synthetic route, which can be better controlled from the molecular precursor to the reaction parameters, such as the reaction time and temperature, to give highly pure and homogeneous materials. The technique allows low reaction temperatures, and controllable size and morphology of the products [11]. Although there have been some reports about the hydrothermal synthesis and properties of rare earth orthoborate YBO3:Tb3+, all of them were focused on YBO3:Tb3+ which show the characteristic green emission under VUV excitation. To the best of our knowledge, few studies about hydrothermal synthesis of YBO3:Tb3+ which show strong red/white light emission under VUV excitation have been reported.

Herein we report an efficient surfactant-free hydrothermal approach to synthesize hexagonal YBO3:Tb3+ with novel self-assembled 3D architectures. These microflowers, which were composed of nanosized units, were expected to maintain the desirable properties of YBO3:Tb3+ nanocrystals (flakes) while being quite stable on the micrometer scale. In spite of the moderate reaction temperature of 180 °C, the as-synthesized YBO3:Tb3+ is highly crystalline. The luminescent properties of the flowerlike YBO3:Tb3+ composed of nanoflakes have also been investigated.

Section snippets

Experimental

All chemicals were analytically pure and were used without further purification. For the synthesis of the YBO3:Tb3+ microflowers, 10 mL of an aqueous solution (0.2 mol L−1) of yttrium nitrate hexahydrate [Y(NO3)3·6H2O] mixed with Tb3+, according to the molar ratio Y:Tb = 8:2, 7:3, 6:4, 5:5, 4:6, respectively, was prepared. Then, 0.3708 g (6 mmol) of H3BO3 (100% excess) were mixed under stirring and deionized water was added to the above mixture to reach 40 mL for total volume. The solution was stirred

Crystallite structure, morphology analyses

It is well known that rare earth ions have similar radius, coordination structure and physical-chemical properties. When one Y3+ is replaced by Tb3+, the crystal structure does not change dramatically [12]. The crystalline structure and phase purity of all the as-formed YBO3:Tb3+ flowerlike products through the hydrothermal process were characterized by X-ray diffraction (XRD) and showed similar crystalline structure. All diffraction peaks of the as-obtained white products (Fig. 1) can be

Conclusions

In summary, a simple and mild hydrothermal method has been demonstrated for the synthesis of the fine, dispersed and homogeneous YBO3:Tb3+ microflower structures assembled from YBO3:Tb3+ nanoflakes. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on a homocentric layer-by-layer growth style. Due to the different luminescent intensity with the different molar ratio of Y–Tb, YBO3:Tb3+ phosphors exhibit

Acknowledgements

This work was supported by the Hubei Province Nature Science Foundation (2010CDB04701) and the Hubei Province Education Office Key Research (D20101011, D20091006) of China.

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