Elsevier

Optical Materials

Volume 33, Issue 8, June 2011, Pages 1252-1257
Optical Materials

Influence of excitation wavelengths on luminescent properties of Sr3Al2O6:Eu2+, Dy3+ phosphors prepared by sol–gel-combustion processing

https://doi.org/10.1016/j.optmat.2011.02.048Get rights and content

Abstract

Eu2+ and Dy3+ ion co-doped Sr3Al2O6 red-emitting long afterglow phosphor was synthesized by sol–gel-combustion methods using Sr(NO3)2, Al(NO3)3·9H2O, Eu2O3, Dy2O3, H3BO3 and C6H8O7·H2O as raw materials. The crystalline structure of the phosphors were characterized by X-ray diffraction, luminescent properties of phosphors were analyzed by fluorescence spectrophotometer. The effect of excitation wavelengths on the luminescent properties of Sr3Al2O6:Eu2+, Dy3+ phosphors was discussed. The emission peak of Sr3Al2O6:Eu2+, Dy3+ phosphor lays at 516 nm under the excitation of 360 nm, and at 612 nm under the excitation of 468 nm. The results reveal that the Sr3Al2O6:Eu2+, Dy3+ phosphor will emit a yellow–green light upon UV illumination, and a bright red light upon visible light illumination. The emission mechanism was discussed according to the effect of nephelauxetic and crystal field on the 4f65d1  4f7 transition of the Eu2+ ions in Sr3Al2O6. The afterglow time of (Sr0.94Eu0.03Dy0.03)3 Al2O6 phosphors lasts for over 600s after the excited source was cut off.

Highlights

► The emission spectra of Sr3Al2O6:Eu2+, Dy3+ phosphors depend on excitation wavelength. ► The emission peak lays at 516 nm under the excitation of 360 nm. ► The emission peak lays at 612 nm under the excitation of 468 nm. ► This phenomenon is caused by the effect of nephelauxetic and crystal field on the emission of the Eu2+.

Introduction

Eu2+ and Dy3+ co-activated strontium aluminates have been widely studied since it has good luminescent properties such as high initial luminescent intensity, long lasting time and good stability. Nowadays most of the commercial long afterglow phosphors based on strontium aluminates have the emitting wavelength located at the short side of the visible region, such as yellow–green [1] or blue–green light [2]. From the view point of practical applications, the light which emits wavelength located at the longer side (red or orange) is more suitable for illuminating light sources and is appropriate for various displays, but the progress on red phosphor strontium aluminates is very slow until the red long afterglow phenomenon is reported in Sr3Al2O6:Eu2+, Dy3+ [3], [4], [5], [6].

However, the descriptions of the photoluminescence of Eu2+ and Dy3+co-activated Sr3Al2O6 were different, some conflict conclusions were presented. It was reported by some researchers that Sr3Al2O6:Eu2+, Dy3+ yields high bright red luminescence with one broad peak, centering at about 610 nm, at room temperature [3], [4], [5], [6], while another group claimed that the peak of the emission spectrum of Sr3Al2O6:Eu2+, Dy3+ was located at 512 nm [7]. So there might be something controversial about the luminescent properties of Sr3Al2O6:Eu2+, Dy3+, and readers might get confused by those conflict reports. Therefore, it seems that some intensive works are still needed to clarify the photoluminescent behavior of Sr3Al2O6:Eu2+, Dy3+.

In this work, Sr3Al2O6:Eu2+, Dy3+ phosphors were prepared by sol–gel-combustion process. The effects of excitation wavelength on the luminescent properties of Sr3Al2O6:Eu2+, Dy3+ were investigated and this influence mechanism was also discussed according to the effect of nephelauxetic and crystal field on the 4f65d1  4f7 transition of the Eu2+ ions in Sr3Al2O6.

Section snippets

Experimental

Eu2O3, Dy2O3, Al(NO3)3·9H2O, Sr(NO3)2, H3BO3 and C6H8O7·H2O were used as raw materials. The raw materials were weighted according to the composition of (Sr0.94Eu0.03Dy0.03)3Al2O6. Al(NO3)3·9H2O, Sr(NO3)2 and C6H8O7·H2O were dissolved in deionized water, and Eu2O3 and Dy2O3 were dissolved in concentrated nitric acid. Then two solutions were mixed. The amount of citric acid in mole was two times that of the metal ions. The H3BO3, as a flux to facilitate the grain growth of strontium aluminates

Phase composition of the synthesized phosphors

Fig. 1 shows XRD pattern of (Sr0.94Eu0.03Dy0.03)3Al2O6 phosphors prepared at 1200 °C for 2 h. This pattern is confirmed to be in accordance with power date in PDF Card No. 24–1187 (Fig. 1b), and no peak of any other phase is detected, indicating that pure-phased Sr3Al2O6 phosphors is formed with cubic structure. The result also indicates that the doped ions, Eu2+, Dy3+ and B3+, formed solid solution within the cubic structure, rather than forming new compounds in the synthesized phosphors.

Photoluminescence of Eu2+, Dy3+ activated Sr3Al2O6 phosphor

The

Conclusions

The red long afterglow Sr3Al2O6:Eu2+, Dy3+ phosphors can be synthesized by sol–gel-combustion synthesis processing, along with heating the resultant combustion ash precursor powder at 1200 °C in a weak reductive atmosphere containing active carbon. The phosphors have pure cubic Sr3Al2O6 phase. The Sr3Al2O6:Eu2+, Dy3+ phosphor will emit a bright yellow–green light upon UV illumination, and a red light upon visible light illumination, which was caused by the effect of nephelauxetic and crystal

Acknowledgment

This work was financially supported by the National Nature Science Foundation of China (Grant No. 51072128).

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