Mesoporous nanocomposite coatings for photonic devices: sol–gel approach Shumaila Islam 1 • Noriah Bidin 1 • Saira Riaz 2 • Lau Pik Suan 1 • Shahzad Naseem 2 • Mohd. Marsin Sanagi 3 Received: 14 June 2016 / Accepted: 12 September 2016 / Published online: 4 October 2016 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract Thermally stable, optically active inorganic nanocomposites, i.e., aluminum–silicate (AS) and silica– titania (ST), are synthesized via acid-catalyzed low-tem- perature sol–gel method in order to get stable, crack-free coating material for photonic devices. The samples are characterized by atomic force microscope, field emission scanning electron microscope (FE-SEM), energy-disper- sive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer– Emmett––Teller (BET) surface area, Barrett–Joyner–Hal- enda (BJH) pore size distribution surface analysis and UV– Vis spectroscopy. Microscopic results show good incor- poration of ST and AS particles as composites with grain size within range of 12–17 and 62–109 nm, respectively. EDX analysis substantiated the stoichiometric formation of homogeneous nanocomposites. XRD of the films reveals primary polycrystalline anatase titania phase and mullite phase of ST and AS nanocomposites. FTIR confirms the heterogeneous bond linkage between titania, silica and alumina species. Furthermore, the fabricated samples have mesoporous nature with high surface area, large pore vol- ume and diameter. The tunable refractive index of 1.33–1.35 with high transparency is obtained for synthe- sized nanocomposites. The experimental findings show that these physically modified and thermally stable alumina- and titania-doped silica-based composite coatings are promising for photonic devices modification. 1 Introduction Since several decades, nanostructured composite films have significant importance with potential applications in various fields such as electronics, optics, biochemistry and photonics [1]. In optoelectronic devices, they have vital importance due to their high porosity, low and high refractive index and low-dielectric-constant thin films. For energy conversion in solar cells, interference filters and light-harvesting, nanocomposite films have also been studied. Specifically, in order to improve light outcoupling from light-emitting devices (LEDs), polymer films and inorganic nanoporous layers have been developed. More- over, packaging in LEDs has essential and critical impor- tance because of three important features, i.e., an electrical connection, a thermal connection and a transparent encapsulation, which protects the chip from environment and modifies light extraction/outcouple of the generated light [2]. Mostly, polymers and silicon were chosen within varying range of refractive index around 1.5–1.8 [1, 2]. The & Shumaila Islam shumaium@yahoo.com Noriah Bidin noriah@utm.my Saira Riaz saira_cssp@yahoo.com Lau Pik Suan piksuan88@gmail.com Shahzad Naseem shahzad_naseem@yahoo.com Mohd. Marsin Sanagi marsin@kimia.fs.utm.my 1 Laser Centre, Ibnu-Sina Institute for Scientific and Industrial Research, University Teknologi Malaysia, 81310 Johor Bahru, Malaysia 2 Centre of Excellence in Solid State Physics, University of the Punjab, Lahore, Pakistan 3 Chemistry Department, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia 123 Appl. Phys. A (2016) 122:935 DOI 10.1007/s00339-016-0430-z