Elsevier

Dyes and Pigments

Volume 143, August 2017, Pages 190-195
Dyes and Pigments

Preparation of color tuned highly emissive long-lasting phosphor with warm-toned emitting color based on coating red-emitting coumarin fluorescent dye color converter and PMMA on SrAl2O4:Eu2+, Dy3+ phosphor

https://doi.org/10.1016/j.dyepig.2017.04.019Get rights and content

Highlights

  • The fluorescent color of PMMA/RECC@SAOED was the mixture of SAOED and FP.

  • The emitting color of PMMA/RECC@SAOED could be adjusted by changing RECC content.

  • Coating of RECC has negative effect on the afterglow brightness of PMMA/RECC@SAOED.

  • Fluorescent color of PMMA/RECC@SAOED tended to red-shift with the increase of RECC.

  • PMMA/RECC@SAOED showed reddish emitting color when the concentration of RECC was 0.9%.

Abstract

A color tuned highly emissive long-lasting phosphor PMMA/RECC@SAOED with warm-toned emitting color was prepared by coating a red-emitting coumarin fluorescent dye color converter (RECC) and PMMA on the surface of green emitting SrAl2O4:Eu2+, Dy3+ (SAOED) phosphors. After being characterized by SEM, FT-IR spectra, photoluminescence (PL) spectra, CIE color coordinates and afterglow decaying curve, the results demonstrated the feasibility of the prepared RECC as the warm-toned color converter for the green-emitting SAOED. After being coated with color converter, the PL spectra of PMMA/RECC @SAOED consisted of two broad bands with two emission peaks at 520 nm and 610 nm, and the intensity of spectra in the range of (576–700) nm increased gradually with the increase of color converter content. The emitting color of the PMMA/RECC@SAOED could be easily controlled by adjusting the concentration of color converter, and it moved to yellow, orange and reddish when the concentration of color converter was added to 0.3%, 0.5% and 0.9%.

Introduction

The long-lasting phosphors (LLPs) are a kind of environmentally friendly photoluminescence materials with long afterglow duration time after the removal of the excitation light source [1], [2]. Since the first report of aluminate long lasting phosphor SrAl2O4:Eu,Dy, the aluminate and silicate LLPs doped with rare earths ions have drawn a great deal of attention because of the advanced properties, such as high luminescence intensity, long persistent time, environmental friendly, no radioactivity as well as high physical and chemical stability [3]. In recent years, the green emitting aluminate and blue emitting silicate LLPs have been widely applied in people's daily life, such as recreation decoration, luminous paints, luminous fiber and fabric, security and emergency signalization and medical optoelectronics detection devices [4], [5], [6], [7], [8], [9], [10].

Usually the emitting color, luminescence intensity and afterglow lasting time are the most important properties for the application of the LLPs. Even though the luminescence intensity and the lasting time of the present commercial used aluminate and silicate LLPs have been highly improved with the help of new synthesis method and new rare earths additive, the luminescence emission color is limited to cool-toned color of green and blue, which is too monotonous and restricts the application areas of the LLPs to some extent. The recent increase in demand for multi-colored LLPs has spurred the rapid development of warm-toned LLPs. Although several kinds of LLPs with warm-toned emitting color have been published recently, for instance, orange-yellow emitting Li2SrSiO4:Eu2+,Dy3+ and Sr3Al2O5Cl2:Eu2+,Tm3+ [11], [12], orange emitting Ca2Si5N8:Eu2+,Tm3+ [13], orange-reddish emitting SrSnO3:Sm3+ [14], orange-red emitting SrS:Eu2+,Pr3+ [15], and red-emitting Y2O2S:Eu3+,Zn2+, Ti4+ [16], very few of them can satisfy the requirement of the commercial application because of the low luminescence intensity and short afterglow duration time.

Instead of taking much time and effort to synthesize new kinds of LLPs with warm-toned emission color and high luminescence intensity, utilizing the color converter to solve the problems associated with the aluminate and silicate LLPs may be a better choice. This task can be accomplished by coating a red fluorescent color converter on the surface of the LLPs. As a result of the excellent luminescence intensity and long afterglow duration time, as well as low synthesis cost, we choose the green emitting SrAl2O4:Eu2+, Dy3+ (SAOED) as the core LLPs. Besides, the selection of the red-fluorescent color converter which can be excited by the core LLPs SAOED is also significant to the realization of this task. According to our previous work, a red-emitting coumarin fluorescent dye color converter (RECC) that can be excited by the green color fluorescence emitted by SAOED was successfully prepared.

In this work, we proposed a color tuned highly emissive LLPs with warm-toned emitting color based on coating of a red-emitting coumarin fluorescent dye color converter and PMMA on the surface of SAOED (PMMA/RECC@SAOED). The SEM, FT-IR, photoluminescence (PL) spectra, CIE chromaticity coordinates, and afterglow decaying properties of the samples were systematically investigated, and the potential luminescence mechanism of the SAOED after being coated by the RECC was also discussed. We do hope the results of the work can offer a novel method to obtain LLPs with warm-toned emitting color from the angle of color converter.

Section snippets

Preparation of the samples

The selected LLPs SAOED were prepared by the high temperature solid state reaction method, the specific proportions of the starting raw materials, SrCO3, Al2O3, Eu2O3, Dy2O3 were determined according to the stoichiometric formula of Sr0.95Al2O4:Eu2+0.02, Dy3+0.03. Besides, 5mol% of H3BO3 was added as a flux. After sufficient blending of the raw materials, the mixture was sintered at 1300 °C in a weakly reducing atmosphere to obtain the green emitting SAOED [17]. The RECC was prepared by

SEM analysis

Fig. 2 shows the SEM photographs of the obtained green-emitting LLPs SAOED prepared by high temperature solid state reaction method and the PMMA/RECC@SAOED samples coated with various content of color converters. It can be seen that the uncoated SAOED shows an irregular pebble shape with average diameter of 8 μm and relatively smooth surface, whereas PMMA/RECC@SAOED samples present a coarse surface with an increased diameter of 12 μm. The formation of the coating layer of PMMA and color

Conclusions

In summary, we successfully prepared a color tuned highly emissive LLPs PMMA/RECC@SAOED with warm-toned emitting color by coating a RECC and PMMA on the surface of green emitting SAOED phosphors. The PL emission spectra of the PMMA/RECC@SAOED samples were composed of the emission spectrum of SAOED and its color converter, which contain two emission peaks at 520 nm and 610 nm, and the relative intensity of the emission spectra decreased gradually in the range of (450–575) nm, whilst also

Acknowledgements

This work was financially supported by College Industrialization Project of Jiangsu Province (NO. JH10-29), National Natural Science Foundation of China (NO. 21171074), Fundamental Research Funds for the Central Universities (NO. JUSRP51505), Ordinary University Graduate Students Academic Degree & Scientific Research Innovation Projects for Jiangsu Province (NO. KYLX16_0796) and A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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