Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig Perylene-embedded electrospun PS fibers for white light generation Tugrul Guner a,1 , Erkan Aksoy b,1 , Mustafa M. Demir a,** , Canan Varlikli c,* a Department of Materials Science and Engineering, Izmir Institute of Technology, Izmir, Turkey b Institute of Solar Energy, Ege University, Izmir, Turkey c Department of Photonics, Izmir Institute of Technology, Izmir, Turkey ARTICLE INFO Keywords: Perylene diimide Solid state emission Polystyrene fiber Frequency down-conversion Aggregation ABSTRACT Perylene dyes have been employed in the fabrication of white light due to their superior photophysical prop- erties and relatively easy synthetic methods. However, their molecular aggregation in solid state is one of the main handicaps since it causes deviation in their optical properties and quenches photoluminescence quantum yields (Φ f ). Investigation of the photophysical properties of a green (PTE), a yellow (PDI) and a new red (DiPhAPDI) emitting perylene derivative in solution, drop-casted films, polystyrene (PS) fibers and PS fibers embedded in poly (dimethyl siloxane) (PDMS) showed that PS:dye fibers prevent aggregation to some extend and allows high Φ f of dyes. The Φ f values of PTE, PDI and DiPhAPDI were all higher than 93.0% in solution and 84.8%, 94.3% and 73.6%, respectively in PS:dye fibers. Embedding the fibers in PDMS improved the photo- stabilities of the dyes two folds compared to their solution phases. The prepared dye containing fibers were combined together into a single PDMS film and utilized as a frequency conversion layer on a blue LED. Fabricated samples were found to show high color rendering index (≥90), adjustable CCT (7500 K–5000 K), and power efficiency values exceeding 200 l m/W depending on the used fiber amount in mass. 1. Introduction It is recognized that 20% of worldwide electricity production is consumed in lighting. Compared to an equivalent incandescent lamp, light emitting diodes (LEDs) may provide 80% energy saving [1,2]. In white light LED generation, two main strategies are followed; multi- chip configuration and phosphor conversion [3]. In the former, three main colors; red, green and blue are obtained from LED chips in- dividually. Even though the resulting white light shows high Color Rendering Index (CRI) and low Correlated Color Temperature (CCT), this process involves a high cost and complex fabrication process [4,5]. The main reason of this complexity is the different driving voltage/current requirements of these individual chips. On the other hand, the latter case requires only a single blue or UV LED chip, and frequency con- version layer on top of it [6–8]. Although in both cases efficiency de- grades as the LED heats up during operation and this can cause a color shift, frequency down-conversion is the most widely used approach because of the application simplicity it provides [2]. Frequency conversion layer mainly consists of inorganic phosphors or polymer/phosphor composites. A mainstream design of such a system contains a yellow phosphor, namely Cerium doped Yttrium Aluminum Oxide (YAG:Ce 3+ ), and a blue LED chip which unfortunately suffers from high CCT and low CRI due to its deficiency of red emission region. In this sense, research on introduction of new rare-earth ele- ment containing phosphors [9,10], rare-earth element free phosphors [11,12], perovskites [13,14] and organic phosphors [15–20] is con- tinued. Among those, organic phosphors are the promising materials due to their abundancy, absorption and photoluminescence (PL) wa- velength tunability, and high PL efficiency. Perylene diimides (PDI) and their derivatives are π-conjugated materials those can be used in photovoltaic devices, sensors, LEDs, and field effect transistors due to their strong visible range absorption, high PL quantum yield, high photostability and thermal durability [15–17,21–30]. However, the PL color of regular PDIs is limited with yellow region and their PL is quenched in their films and solid states due to intermolecular π-π interactions. To overcome these problems, several methods including copolymerization approach [18], 3D func- tionalization [22,26,27,31,32], molecular isolation [33], or self-as- sembly monolayer formation [34] have already been attempted. All those attempts either limited the new structure with regular PDI https://doi.org/10.1016/j.dyepig.2018.08.040 Received 17 June 2018; Received in revised form 19 August 2018; Accepted 21 August 2018 * Corresponding author. ** Corresponding author. 1 Author contributions: First and second authors contribute equally to the manuscript. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. E-mail addresses: mdemir@iyte.edu.tr (M.M. Demir), cananvarlikli@iyte.edu.tr (C. Varlikli). Dyes and Pigments 160 (2019) 501–508 Available online 23 August 2018 0143-7208/ © 2018 Elsevier Ltd. All rights reserved. T