Short communicationDesign of long-term stable red-emitting CsPb(Br0.4, I0.6)3 perovskite quantum dot film for generation of warm white light
Introduction
Light emitting diodes (LEDs) have attracted high interest in the lighting market and are expected to be progressive materials in solid state lighting technology. White light emitting diodes (LEDs) have been replacing conventional lighting systems such as fluorescent lamps and incandescent lamps because of their advantages of high energy efficiency, long lifetime, low-power consumption and environmental protection [1], [2], [3]. The general method for producing white light involves the combination of blue-light-emitting InGaN chips with yellow Y3Al5O12:Ce3+ cerium doped yttrium aluminum garnet (YAG: Ce) phosphor materials [4], [5], [6]. Since YAG: Ce works through the 5d-4f transition of Ce3+ ion, the spectrum of luminescence has broad absorption bands in the range of 300–500 nm compared with 4f-4f transitions for most rare-earth ions [4], [7]. Although White LEDs using the YAG: Ce phosphor play an important role in the generation of white light, the production of warm white light with both a low color rendering index (CRI) value and a high correlated color temperature (CCT) is a challenging task because of the lack of a red component [8], [9]. For the realization of warm white light, relatively lower CCT (<4000 K) and CRI (>80) values are required for illumination [3], [10]. Abdelhay Aboulaich et al. reported the association of YAG: Ce nanoparticles with free-Cd CuInS2/ZnS core/shell quantum dots (QDs) for application in white light emitting diodes (WLEDs), which show higher CRI of about 84 and warm white light with CCT of 2784 K [11]. Hyun Suk Jung et al. reported fine tuning the emission color of YAG: Ce-based white WLEDs by applying CdSe/CdS/ZnS QDs onto the surface of YAG: Ce nanoparticles, resulting in high CRI of 92.82, and low CCT of 2617 K [12]. The above procedures are ideal for the generation of warm white light because of the excellent optical properties of QDs such as narrow emission band, high photoluminescence quantum yield, and high charge carrier mobility [13]. Despite being a good candidate as a next generation lighting source, it is difficult to use QDs in White LEDs owing to the cost of the materials and encapsulation problems as well as the complicated process required to produce the QDs. In recent years, organometallic halide perovskite materials have become attractive materials for applications in photovoltaics and photodetectors as well as light emitting diodes (LEDs) because of their outstanding properties [14]. Yuansheng Wang et al. reported inorganic halide perovskite QDs using PMMA with YAG: Ce for white LEDs [15]. However, PMMA-based Perovskite QDs were found to be susceptible to degradation in our previous research. Therefore, it is important to resolve the issues with encapsulation. In this research, we report warm white LEDs created via the fabrication of red emitting CsPb(Br0.4, I0.6)3 perovskite QDs films on the surface of YAG: Ce phosphor with ethyl cellulose for the improvement of luminescence as well as stability and degradation in the air.
Section snippets
Experimental procedure
All chemicals were used without further purification. Lead bromide (PbBr2, 99.8%), Lead iodide (PbI2, 99.8%), Cesium carbonate (Cs2CO3), 1-Octadecene (ODE, 90%), Oleylamine (OLA, 80–90%), and Oleic acid (OA, 90%), anhydrous toluene, ethyl cellulose (EC), and Poly(methyl methacrylate) (PMMA, Mw = 15,000) were purchased from Sigma-Aldrich. High efficient red emitting perovskite CsPb(Br0.4, I0.6)3 QDs were produced with the following method. For the preparation of 0.1 M Cs-oleate, a mixture of CsCO3
Results and discussion
Fig. 2(a)-(c) show the basic characteristics of the red emitting ECQD film. Fig. 2a shows the PL emission spectrum of the prepared sample. A high efficient emission band centered at 641 nm with a narrow full width at half maximum (FWHM) of 32 nm is observed, and is applied to both the display and lamp technology. Also, the PLQY under excitation at 450 nm is 34.2%. The measured data for the red emitting ECQD film show a high absorbance of 64.9% and the Commission International de l’Eclairage (CIE)
Conclusion
In the current article, we successfully fabricated red-emitting ECQD film for warm white light generation. High quality red-emitting ECQD films were obtained with FWHM of 42 nm as well as high absolute PLQY of 34.2%. Additionally, the prepared ECQD samples were located in the deep red region for warm white light unlike YAG: Ce and (Ca, Sr)SiAlN3: Eu2+ films. This provides a potential candidate with highly desirable characteristics for both lamp and display technology. Red-emitting ECQD film YAG:
Acknowledgements
This work was supported by the Future Materials Discovery Program (NRF-2016M3D1A1027664) through the National Research Foundation under the Ministry of Science, ICT & Future Planning. This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20153030012560).
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These authors contributed equally.