Hybrid nanospheres of silica covalently containing yellow-emitting cationic iridium(iii) complex: preparation and application in white light-emitting diodes

Abstract

A yellow-emitting cationic iridium(III) complex [(dfppy)₂Ir(TBD)]PF₆ (TBD: N⁴,N^4′-bis(3-(triethoxysilyl)propyl)-[2,2′-bipyridine]-4,4′-dicarboxamide; dfppy: 2-(2,4-difluorophenyl)pyridine) containing hydrolysable alkoxysilanes was synthesized. Then, a series of silica-based hybrid nanospheres with diameters of around 400 nm was prepared via the hydrolysis of this complex together with tetraethyl orthosilicate (TEOS, a silica source). When the amount of the complex used was 5.0 wt%, hybrid nanospheres showed the best photoluminescence (PL) properties, relative to the PL quantum yield of pure solid [(dfppy)₂Ir(TBD)]PF₆ (12.7%), that of hybrid nanospheres increased to 26.2%. Moreover, the thermal decomposition temperature (T_d) of pure solid [(dfppy)₂Ir(TBD)]PF₆ was 331 °C, the T_d of the complex in hybrid nanospheres increased to 447 °C. However, the yellow light emission was almost unchanged and was still located at 500–750 nm with a maximum wavelength (λ_em,max) of 577 nm. Under the excitation of blue-emitting chips (λ_em,max ≈ 455 nm), cold/neutral/warm white light-emitting diodes (WLEDs) with good luminous quality can all be fabricated using these hybrid nanospheres as phosphors in epoxy resin at different blending concentrations. Compared with two or three iridium(III) complexes being contained in silica-based particles as phosphors as described in literatures, in this study, silica-based hybrid nanospheres covalently containing only one yellow-emitting cationic iridium(III) complex as phosphors provide a more effective and simpler method for preparation high-performance WLEDs.