Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Warm white light-emitting diodes using organic–inorganic halide perovskite materials coated YAG:Ce 3+ phosphors Lung-Chien Chen ⁎ , Zong-Liang Tseng, Wei-Wen Chang, Yen Wen Lin Department of Electro-optical Engineering, National Taipei University of Technology, 1, 3 s., Chung-Hsiao E. Rd., Taipei 106, Taiwan ARTICLE INFO Keywords: YAG phosphors Perovskite phosphors White LEDs GaN ABSTRACT This work reports warm white light-emitting diodes (WLEDs) using organic–inorganic halide perovskite mate- rials coated YAG:Ce 3+ phosphors by a liquid phase synthesis method. The perovskite MAPbBr 3-x I x -coated YAG:Ce 3+ phosphors have more red light contribution than YAG:Ce 3+ phosphors without the perovskite coating. The chromaticity coordinate of white LED with YAG:Ce 3+ remote phosphor is (x = 0.3134, y = 0.3497) 6359. However, those of MAPbBr 2.5 I 0.5 and MAPbBr 2.0 I 1.0 -coated YAG:Ce 3+ remote phosphor shift to (x = 0.4220, y = 0.3725) 2908 and (x = 0.4067, y = 0.4028) 3525, respectively. The colors of perovskite-coated samples are more red and warm. Therefore, the perovskite-coated YAG:Ce 3+ method is useful for warm WLED. 1. Introduction White light-emitting diodes (WLEDs) have developed for solid-state lighting due to their high luminosity, high energy conversion efficiency and long lifetime [1–4]. Up to now, the combination of a blue-emitting GaN light-emitting diode (LED) and yellow phosphors Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) is most commonly used as WLEDs. However, high corre- lated color temperature (CCT) or low color rendering index (CRI) is obtained in the devices due to insufficient red light contribution, which limits their certain applications, such as indoor lighting. Several tech- niques have been developed to increase the CRI or decrease the CCT. The most popular method is that red phosphors are introduced into the blue LED and YAG:Ce 3+ system to enhance the red region of the spectral emission characteristics of YAG:Ce 3+ . Red phosphors such as nitride [5,6] (B 2 Si 5 N 8 :Eu 2+ and BAlSiN 3 :Eu 2+ (B = Ca, Sr and Ba)) and fluoride [7–10] (A 2 AlF 6 : Mn 4+ and A 3 DF 6 : Mn 4+ (A = Li, Na, K and Rb; D = Si, Ge, Sn)) are widely used in warm WLED devices. However, this method requires extra red phosphors, resulting in complex pro- cesses and higher cost. On the other hand, organic halide perovskites materials have drawn a great deal of attention due to their potential in photovoltaic [11–13] and light-emitting devices [14–16]. They can be prepared by low-cost and low-temperature solution processes and still exhibit large absorp- tion coefficients, ultralow bulk defect densities and slow Auger re- combination [17], which are attractive for a wider range of the practice optoelectronic applications [18]. Their visible photoluminescence (PL) tunability (400–800 nm) can be straightly achieved by halide ion sub- stitution in CH 3 NH 3 PbX 3 chemical structures (or MAPbX 3 ) [17,19]. Therefore, it is interesting to employ excellent characteristics of the perovskite materials to improve CRI and CCT of the WLEDs. Herein, we report another method, which potentiates the spectra of YAG:Ce 3+ phosphors using organic–inorganic halide perovskites ma- terials, to enrich the red light emission region. The method employs a simple and rapid grinding process to coat CH 3 NH 3 PbBr 2.5 I 0.5 and CH 3 NH 3 PbBr 2.0 I 1.0 on the surface of the YAG:Ce 3+ powders, which requires very low material cost and no high temperature sintering treatments The warm WLEDs based on the perovskite materials have also demonstrated, leading the improved CCTs compared to the tradi- tional YAG:Ce 3+ based WLEDs. 2. Experiments Methylammonium bromide (MABr; Lumtec.Inc.), Methylammonium iodide (MAI; Lumtec. Inc.), PbBr 2 (Sigma-Aldrich. Inc.), and PbI 2 (Sigma- Aldrich. Inc.) were dissolved in dimethylformamide (DMF) by mixing an molar ratio of 1:1-x:x as a MAPbBr 3-x I x precursor solution of 0.3 M. All of them were directly used without any further purification. The perovskite precursor solution (10 μL) was drop onto YAG:Ce 3+ powder (Titec Corporation Ltd., 0.2 g) placed in an agate mortar and then they were grounded by using an agate pestle. During grindings, small amount of DMF was added to mix the raw materials homogenously. The processing flow diagram was shown in Fig. 1. After grindings, the mixed powders dried at room temperature for 3 h in the air. The perovskite coated YAG:Ce 3+ powder can be easy and rapid fabrication, which showed in the supporting video file (MAPbBr 2.5 I 0.5 -coated YAG powders). The crystalline character- istics of the powder were observed by PANalytical X'Pert Pro DY2840 X-ray https://doi.org/10.1016/j.ceramint.2017.11.176 Received 12 October 2017; Received in revised form 22 November 2017; Accepted 24 November 2017 ⁎ Corresponding author. E-mail addresses: ocean@ntut.edu.tw (L.-C. Chen), tw78787788@yahoo.com.tw (Z.-L. Tseng). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2017 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Chen, L.-C., Ceramics International (2017), https://doi.org/10.1016/j.ceramint.2017.11.176