Applied Surface Science 303 (2014) 319–323 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Photoluminescence emission from Alq3 organic layer in metal–Alq3–metal plasmonic structure Bohr-Ran Huang a , Chung-Chi Liao a , Wan-Ting Fan b , Jin-Han Wu c , Cheng-Chang Chen c , Yi-Ping Lin c , Jung-Yu Li c , Shih-Pu Chen c , Wen-Cheng Ke d , Nai-Chuan Chen b,∗ a Graduate Institute of Electro-Optical Engineering and Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan b Institute of Electro-Optical Engineering and Department of Electronic Engineering, Chang Gung University, Tao-Yuan 333, Taiwan c Green Energy and Environment Research Laboratories, Industrial Technology Research Institute (ITRI), 195, Sec. 4, Chung-Hsin Road, Chutung 310, Taiwan d Department of Mechanical Engineering, Yuan Ze University, Tao-Yuan 320, Taiwan a r t i c l e i n f o Article history: Received 18 November 2013 Received in revised form 27 February 2014 Accepted 27 February 2014 Available online 12 March 2014 Keywords: Surface plasmon polarition (SPP) Dispersion relation Metal–insulator–metal (MIM) Light extraction efficiency a b s t r a c t The emission properties of an organic layer embedded in a metal–organic–metal (MOM) structure were investigated. A partially radiative odd-SPW as well as a non-radiative even-SPW modes are supported by hybridization of the SPW modes on the opposite organic/metal interface in the structure. Because of the competition by this radiative SPW, the population of excitons that recombine to form non-radiative SPW should be reduced. This may account for why the photoluminescence intensity of the MOM sample is higher than that of an organic–metal sample even though the MOM sample has an additional metal layer that should intuitively act as a filter. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Because of the characteristics of self-emission, high bright- ness, large viewing angle, short response time, and flexibility, organic light-emitting diodes (OLEDs) are emerging as alternatives for general lighting and displays and are fueling the innova- tion of associated applications. Despite these achievements, a great potential to enhance their light output efficiencies still exists, because, as indicated by Nowy and Hong [1,2], the light extraction efficiency for a typical device is only about 16–20%. This low extraction efficiency is caused by two factors. The first is related to the close proximity of the light-emitting layer to the metallic electrode. The close proximity is designed to com- pensate for the low carrier conductivity in organic layer to suppress the operating voltage. However, because the distance is shorter than the penetration depth of the surface plasmon wave on the metallic electrode, the spontaneous recombination of excitons would favorably excite the non-radiative surface plasmon waves (SPWs) on the metal surface because of the Purcell effect [3,4] and then gradually dissipate as heat because of damping. ∗ Corresponding author. Tel.: +886 3 2118800x5953. E-mail address: ncchen001@mail.cgu.edu.tw (N.-C. Chen). According to the literature [1,2], the loss of extraction efficiency by means of SPWs can account for as much as 40% of the total extraction loss. The second reason is related to the inherent lay- ered structure of OLEDs that inevitably forms waveguides inside the devices. Light trapped inside the waveguides is ultimately absorbed as heat. Waveguides formed by transparent conduct- ing layers and by glass or plastic substrates play leading roles in this loss aspect [1,2]. At present, the general strategy to extract these SPWs or guided modes is the use of grating, corrugation, and metal nanoclusters formed on the surface or embedded at the interface to scatter these trapped waves [5–9]. However, in addi- tion to the associated increase in processing cost and decrease in yield, these extraction structures would potentially degrade device reliability because of current crowding deterioration at each cor- ner of the extraction structures [10,11]. Thus, alternatives that can enhance extraction efficiencies while preventing the aforemen- tioned drawbacks would be valuable. In our previous investigation [12], we recognized that metal–organic layer–metal (MOM) struc- tures would probably be beneficial for these purposes. In a MOM structure, the small distance between the two metal/organic layer interfaces allows SPWs on opposite interfaces to interact with each other and hybridize to form two kinds of SPWs with dis- tinct parities. Although the even-SPW (symmetric magnetic field distribution) is still non-radiative and has a dispersion curve very http://dx.doi.org/10.1016/j.apsusc.2014.02.175 0169-4332/© 2014 Elsevier B.V. All rights reserved.