Effect of catalysts and co-precursors on the photoluminiscence of malachite green dye doped TMOS silica xerogels

Abstract

Malachite green (MG) laser dye doped silica matrix was prepared by sol–gel processing by keeping the molar ratio of tetramethylorthosilicate [TMOS,Si(OCH 3) 4]:methanol:catalytic water:methanolic MG constant at 1:4:5:7 × 10 −4:3 × 10 −6, respectively and varying the catalyst. The effect of acidic and basic catalysts, MG/TMOS molar ratio and co-precursors on the optical properties of the MG doped silica xerogels has been studied. Colourless transparent samples were obtained with strong acids, [hydrochloric (HCl)], [nitric acid (HNO 3)], strong base [sodiumhydroxide (NaOH)] and strong acid–weak base [ammoniumhydroxide (NH 4OH)] mixture and whereas turbid, opaque and light blue coloured samples were obtained with weak base. However, transparent, monolithic and blue coloured MG doped silica xerogels with longitivity of 6 months were obtained with weak acids [acetic acid (CH 3COOH, ACT), citricacid (C 6H 8O 7·H 2O, CTA)]. The MG/TMOS molar ratio was varied from 3 × 10 −8 to 3 × 10 −5 (10 −6 to 10 −3 M of MG) and the absorbance and luminiscence of the MG doped silica xerogels increased with increase in the MG/TMOS molar ratio to 1 × 10 −5 and remained constant for further increase of MG/TMOS molar ratio. Various co-precursors used such as methyltrimethoxysilane (MTMS), ethyltrimethoxysilane (ETMS), methyltriethoxysilane (MTES), ethyltriethoxysilane (ETES), phenyltrimethoxysilane (PTMS), phenyltriethoxysilane (PTES), dimethyldodecyl chlorosilane (DDCS) and dimethyloctadecylmethoxysilane (DOMS) and the absorbance and luminescence of the MG doped silica xerogels increased with addition of MTMS, ETMS, MTES, ETES, PTMS and PTES but decreased with DDCS and DOMS.