Near white light emission of BaY2ZnO5 doped with Dy3+ ions

https://doi.org/10.1016/j.jallcom.2011.11.088Get rights and content

Abstract

Controlling activator concentrations to possess near white light emission of BaY2ZnO5 doped with Dy3+ ions was performed using high energy vibrating milled solid-state reaction. The XRD patterns show that all of the peaks can be attributed to the BaY2ZnO5 orthorhombic structure, because that the BaY2ZnO5 and BaDy2ZnO5 are isostructures with a space group of Pbnm. Under ultraviolet (355 nm) excitation, a weak group of emission peaks appear for the 4M21/24I13/2 + 4K17/2 + 4F7/2  6H13/2 transition at 453 nm, and two groups of strong emission peaks appear at 489 nm and 579 nm, corresponding to the 4F9/2  6H15/2 and 4F9/2  6H13/2 transitions of Dy3+ ions, respectively. The decay curve results indicate that the decay mechanism of the 4F9/2  6H13/2 transition is a single decay component between Dy3+ ions only. In addition, the asymmetry ratio, which is independent of Dy3+ ion concentration, remains at about 1.04, indicating that the symmetry of Dy3+ ions does not change with concentration. Concentration quenching occurs with x values above 0.07, and the critical distance is about 11.93 Å. The CIE color coordinates of x = 0.320 and y = 0.389 are located in the near white light region.

Highlights

► The CIE color coordinates (x = 0.320, y = 0.389) is in the near-white-light region. ► The concentration quenching effect occurs for Ba(Y2−xDyx)ZnO5 when x > 0.07. ► The asymmetry ratio remains at about 1.04, which is independent of the Dy3+ ion.

Introduction

In recent years, inorganic phosphors have been extensively investigated for application in various types of flat panel display (FPD), such as plasma display panels (PDPs), thin film electroluminescence devices (TFEL), field-emission displays (FEDs), and vacuum fluorescent displays (VFDs) [1], [2], [3], [4], [5], [6], [7]. Nichia Chemical and Osram control many of the patents on phosphors, leading outside manufacturers to invest in three-wavelength mixed white lights and the development of novel phosphors. Oxide phosphors have recently received a lot of attention for applications such as screens in PDPs and FEDs and for white-light-emitting diodes due to their higher chemical stability and resistance to moisture compared to those of sulfide/phosphors [8], [9], [10].

Rare earth ion-doped crystal has attracted considerable research interest due to their excellent luminescence properties [11]. The use of rare-earth element-based phosphors, based on line-type f–f transitions, can narrow emissions to the visible range, resulting in high efficiency and high lumen equivalence. Rare-earth Dy3+ ions have two dominant emission bands, one in the blue region (470–500 nm) and one in the yellow region (560–600 nm). The two emissions originate from 4F9/2  6H13/2 and 4F9/2  6H15/2 transitions of Dy3+ ions, respectively. The yellow emission of Dy3+ is especially hypersensitive (ΔL = 2, ΔJ = 2) to the local environment, whereas the blue emission is not. Therefore, by suitably adjusting the yellow-to-blue intensity ratio, it is possible to obtain a phosphor with near-white-light emission. It is the candidate for the potential white light emission phosphor with a single emitting center for luminescent materials doped with Dy3+ ions [12], [13].

BaY2ZnO5 is a kind of luminescence host with a stable crystal structure and high thermal stability. BaY2ZnO5 has an orthorhombic structure with a space group of Pbnm [7]. The basic structure of BaY2ZnO5 consists of YO7, BaO11, and ZnO5 polyhedra. Y is 7-fold coordinated inside a monocapped trigonal prism. These prisms share edges to form wave-like chains parallel to the long b-axis, and two such units join to form the basic structure motif of Y2O11. It is well known that a given optical center in different host lattices exhibits different optical properties due to the changes of the surroundings of the center of a Dy3+-doped phosphor. In the present study, BaY2ZnO5 phosphors doped with various Dy3+ ion concentrations were synthesized using a vibrating mill solid-state reaction and calcined at 1250 °C for 12 h in air. The structure and photoluminescence properties of BaY2ZnO5:Dy3+ were investigated.

Section snippets

Powder preparation

The Dy3+-doped BaY2ZnO5 phosphors formulated Ba(Y1−xDyx)2ZnO5, with x equal to 0.01. 0.2 were synthesized by a vibrating mill solid-state reaction using barium carbide (BaCO3), zinc oxide (ZnO), yttrium oxide (Y2O3), and dysprosium oxide (Dy2O3) with purities of 99.99% (purchased from Aldrich Chemical Company Inc.). The starting materials were weighed in a stoichiometric ratio and ground in a mechanically activated high-energy vibro-mill for 15 min with zirconia balls in a polyethylene jar.

Structure

Fig. 1 shows the XRD patterns of BaY2ZnO5 doped with various Dy3+ ion concentrations and calcined at 1250 °C in air for 10 h. All samples exhibit a single phase which was identified as the BaY2ZnO5 phase (JCPDS Card No. 89-5856) without any impurities, indicating that the Dy3+ ions substituted the Y3+ ions. Using the Rietveld refinement method, Kaduk et al. [14] found that BaY2ZnO5 and BaDy2ZnO5 are isostructures with a space group of Pbnm. The full width at half maximum (FWHM) of the peaks did

Conclusion

A near-white-light emission phosphor, Dy3+-doped BaY2ZnO5, was synthesized by a vibrating mill solid-state reaction, and its luminescence properties were investigated. The XRD patterns show that all of the peaks can be attributed to the BaY2ZnO5 orthorhombic structure when the Dy3+ ion concentration is above 20 mol% because BaY2ZnO5 and BaDy2ZnO5 are isostructures with a space group of Pbnm. Under ultraviolet (355 nm) excitation, a weak group of emission peaks was observed for the 4M21/24I13/2 + 4K

Acknowledgment

The authors would like to thank the National Science Council of the Republic of China for financially supporting this project under Grant NSC 98-2221-E-150-065-MY2.

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