Investigations on the blue luminescence enhancement of organically modified SiO2-TiO2-PDMS glass matrix

Abstract

A novel class of Organically Modified Silicates (ORMOSILs) has been synthesized by non-hydrolytic sol–gel method at low temperature, incorporating the organic polymer, polydimethylsiloxane (PDMS) in tetraethylorthosilicate (TEOS) and titanium (IV) isopropoxide (TIP) based glassy gels. The structural modification of pure SiO2-TiO2 matrix by PDMS and its effects on optical and photoluminescence spectroscopy were investigated in detail. XRD pattern and HR-TEM images confirm the structural modification of the SiO2-TiO2-PDMS glass matrix. The formation of TiO2 nanocrystals of about 5–6 nm in size, embedded in the amorphous SiO2 matrix, has been confirmed from HR-TEM and SAED patterns. The TG–DTA analysis revealed the improved thermal stability of the ORMOSIL and the DSC analysis shows that its glass transition temperature decreases to 55.23 °C. A distinctive enhanced blue emission at 470 nm has been observed in photoluminescence studies of the prepared samples. FT-IR studies confirmed the formation of Ti–O–Ti, Si–O–Ti and Si–CH3 bonds by the PDMS modification of pure SiO2-TiO2 glass. These bonds and TiO2 nanocrystals embedded in the amorphous glass matrix together play an important role in the photoluminescence properties of the ORMOSIL. SiO2-TiO2 matrix has a luminescence quantum efficiency of 22.2% and the PDMS incorporation has increased the quantum efficiency to 55.8%. Thus SiO2-TiO2-PDMS ORMOSIL can be used as an efficient blue emitting host matrix for WLED fabrication.