Anomalous fluorescence in near-infrared Raman spectroscopy of cementitious materials Steven P. Newman a,1 , Simon J. Clifford a,2 , Peter V. Coveney a,2 , Vijay Gupta b , Joanna D. Blanchard b,3 , Frank Serafin b , Dor Ben-Amotz c , Sidney Diamond d, * a Centre for Computational Science, Queen Mary, University of London, London E1 4NS, UK b W.R. Grace and Co.-Conn., 62 Whittemore Avenue, Cambridge, MA 02140, USA c Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA d School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA Received 26 August 2003; accepted 1 October 2004 Abstract The results of near-infrared Fourier transform Raman spectral examination of cement minerals, several commercial Portland cements, and hydrating Portland cements are critically examined. It is shown that structured fluorescent effects dominate the observed spectra for C 3 S, C 2 S, and cement, and none of the bands generated by this mode of examination is a true Raman band. The apparent bands for the Portland cements are in different positions to those for the individual cement minerals. The fluorescence-derived spectra for different cements are similar to each other but vary enormously in intensity for different cements. Hydration progressively reduces the intensity of the bands, but does not generate bands at new locations. It is tentatively suggested that the fluorescence effect may be somehow associated with the status of the cement components as orthosilicates (i.e., composed of isolated silica tetrahedra. Samples of high-purity C 2 S exhibit the fluorescence effect, but samples of CS (wollastonite) of similar purity do not. The latter are metasilicates (i.e., composed of linked chains of silica tetrahedra). They exhibit normal Raman Stokes and anti-Stokes bands. D 2004 Elsevier Ltd. All rights reserved. Keywords: Spectroscopy; Raman spectroscopy; Fluorescence; Ca 3 SiO 5 ; Ca 2 SiO 4 1. Introduction The potential of Raman spectroscopy as an analytical technique for cementitious materials was first demonstrated by Bensted [1–3], nearly three decades ago. Subsequently, Conjeaud and Boyer [4] successfully used a Raman microp- robe to study individual crystals in clinker phases and Portland cements. Since this time, however, Raman spectro- scopy has been used only sparingly to study such materials, probably in part because of strong fluorescence effects generated for many substances under both visible and near- infrared excitation modes. It was generally considered that the development of Fourier transform (FT) Raman spectroscopy with near- infrared excitation in 1986 should eliminate the usual problems of fluorescence experienced in many dispersive Raman examinations by precluding electronic absorption of the incident radiation [5]. Unfortunately, FT Raman studies of cementitious materials with near-infrared excitation have generated ambiguous results. Dyer et al. [6] observed a bvery unusual result concerning the intensity of the spectraQ for near-infrared FT Raman spectra of cement minerals, and concluded that the origin of the bands was probably fluorescence rather than Raman scattering, but these authors were unable to identify the fluorescing species. Subse- quently, Bonen et al. [7] published near-infrared FT Raman 0008-8846/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2004.10.001 * Corresponding author. Tel.: +1 7654945016; fax: +1 7654961364. E-mail address: sidiamond@verizon.ent (S. Diamond). 1 Current address: Nalco, Energy Services Division, Cadland Road, Hardley, Hythe, Southampton SO45 3NP, UK. 2 Current address: Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK. 3 Current address: 23 Hadley Rd., Merrimac, MA 01860, USA. Cement and Concrete Research 35 (2005) 1620 – 1628