J. MATER. CHEM., 1993, zyxwvutsrqp 3(1), zyxwvutsrqpo 11 1-1 12 111 MATERIALS CHEMISTRY COMMUNICATIONS Rare-earth-doped Hybrid Siloxane-Oxide coatings with Luminescent Properties Natalia 1. Koslova, Bruno Viana and Clement Sanchez* zyxwv Laboratoire de Chimie de la Matiere Condensee URA CNRS zyxwv 7466, Universite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris, France Emission and absorption properties of hybrid coatings consisting of a siloxane network crosslinked with mixed metallic alkoxides, obtained by reacting Zr(OPr"), and different rare-earth methoxyethoxides (M = Nd3+,Sm3', Dy3 ', Er3+, Tm3+)are presented. Keywords: Siloxane-oxide ; Coating ; Luminescence ; Zirconium Sol-gel chemistry is based on inorganic polymerization reactions. The chemical synthesis of gels is performed in organic solution at lower temperatures than conventional chemical methods; organic components can therefore be easily preserved in an oxide gel matrix. Luminescence or non-linear optical properties of dyes inside silica or transition-metal oxide based gels have been studied e~tensively.'-~ Trivalent rare-earth ions (RE3 +) have interesting emission properties for laser applications. Most of the studies concerning RE3+ fluorescence and particularly Nd3 have been carried out in crystalline or glassy matrices for which heat treatment at relatively high temperatures has been performed. Fewer studies have been carried out on emission properties of RE3 incorporated inside room-temperature sol--gel matrices.2- To the best of our knowledge, practically no work has been reported on the optical properties of RE3+ inside hybrid organic-inorganic matrices made by the sol-gel process. Mixed oxide-silicone materials are good hybrid matrices for optics6 They can be synthesized by using organically modified silicon alkoxide precursors [SiR',(OR), -J, R' being any organic group (CH,, H, C,H,) which leads to the formation of a siloxane network. The silicone-based network can be crosslinked with metal oxypolymers obtained zyxwvut via hydrolysis of metal alkoxides M(OR), with M=Si, Ti, Zr and A1.6 Mixed siloxane-oxide coatings can be easily prepared. This communication addresses the synthesis of hybrid coatings obtained via hydrolysis of diethoxymethylsilane [DEMS = SiH(OEt),(CH,)] and a mixed metallic alkoxide synthesized by reacting Zr(OPr"), and the rare-earth alkoxide. Some optical properties of the rare-earth compounds (RE3+ = Nd3+, Sm3+,Dy3+,Er3+,Tm3+) are also presented. Rare-earth methoxyethoxides [RE(OR),, OR = methoxy- ethoxy] are synthesized from metal sheets and dry methoxy- ethanol under argon following a previously described electrochemical technique.' After recrystallisation the solid RE3+ methoxyethoxides were stirred and refluxed for 3 h with zirconium propoxide purchased from Fluka (molar ratio Zr : RE = 1) in order to obtain a homogeneous solution even after cooling at room temperature. The formation of mixed oxoalkoxides from Zr and the zyxwvutsrq RE via ether eliminations can probably account for the observed solubility.' Diethoxymethylsilane (DEMS), absolute ethanol and water in a 1 : 1 : 1 molar ratio were mixed for a few minutes under magnetic stirring. The solution fo Zr(OPr"), and a correspond- ing rare-earth methoxyethoxide (RE3+ = Nd3+,Sm3+,Dy3+, Er3+, Tm3+) is then added to the previous solution to give Zr : Si and RE : Si molar ratios of 1 : 9. Hydrogen gas is given off by the sol. This phenomenon is related to the cleavage of Si-H bonds catalysed by the non-silicate alkoxides. Upon such reaction most of the Si-H bonds of the DEMS precursor were cleaved as shown by the weak residual infrared band located at 2 I60 cm- and corresponding to v(Si-H). The sol presents strong IR bands located at 820 and 970 cm- that can be assigned to Si-0-M linkages (M =Zr or RE).9 An appropriate amount of the sol was poured onto the glass sheet, allowed to gel and dried at room temperature. Such coatings were deposited several times until a thin layer of ca. 50-100 pm was obtained. The absorption spectra of the 4f-4f transitions were recorded for all RE3+-doped hybrid coatings. They contained broad transitions due to the strong structural disorder present in these amorphous samples. In this communication only the Nd3+ optical spectra are presented. Fig. 1 presents the Nd3+ absorption spectrum inside the hybrid coating. The 500 zyxwv 600 700 800 900 zy A /nm Fig. 1 Absorption spectrum of the Nd3+-doped hybrid coating Table 1 Emission properties of the RE3+-doped hybrid coatings mean excitation strongest emission e-folding for RE3+ wavelength/ emission wavelength/ 2 x I 02' ions nm in the visible nm ions cm - 3/ps 0.2 Nd3' 798 4F3,2-+41g,2 880 Sm3+ 532 4G, 2-+6H7 610 27 14 13 150 Dy3+ 355 4F9 2j6H13 2 577 Er3+ 355 4s3,2-+4113 2 580 Tm3+ 785 3H4-+3H6 800 Downloaded by North Carolina State University on 20 September 2012 Published on 01 January 1993 on http://pubs.rsc.org | doi:10.1039/JM9930300111 View Online / Journal Homepage / Table of Contents for this issue