JOURNAL OF RAMAN SPECTROSCOPY, VOL. zyxwvuts XI, 813-816 (1989) zyxwvut SHORT CO zyxwv MM UNICA TI0 N zyxwv Stokes and Anti-Stokes Raman Scattering and Electronic Emission Studies on Dysprosium-doped YBa2Cu307-& H. D. Bist, R. Guqar, P. Upadhyay and P. K. Khulbe Department of Physics, Indian Institute of Technology, Kanpur 208 016, India C. V. N. Rao, S. K. Agarwal and A. V. Narlikar National Physical Laboratory, New Delhi, India T. S. Little and J. R. Durig Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208, USA Laserexcited emission from YBa,Cu,O,-, with 7.5% dysprosium nominally substituted in place of yttrium is presented in the range 13000-23 OOO cm-'. In addition to the reported Raman lines in the Cu-0 stretching region, a number of other spectral features were observed. These include a discrete luminescence with zyx lines at 14400 and 14425 cm-' and a broad emission with its peak position and band width varying with excitation wavelength. Additionally, an antiStokes scattering, which zyxwvu has no apparent counterpart in the Stokes region, was observed. These observations may be of significance in the elucidation of the mechanism of high-temperature superconduc- tivity. INTRODUCTION Experimental characterization of the phonon properties and gap structure in the recently discovered high- temperature superconductors (HTSC) is essential in order to determine the extent to which conventional Bardeen-Cooper-Schrieffer (BCS) theory or the Ander- son resonance valence bond (RVB) model or which of their multiple variations is applicable to these materials.' There have been numerous reports on the infrared reflectance spectra and studies of the Raman and inelastic neutron scattering of these materials.' Raman scattering studies on YBa,Cu,O, -d (henceforth YBaCuO) reported in the literature exhibit large dis- crepancies., The observed data depend on several factors such as the source and composition of the parent compounds, the exact method of preparation (calcining, quenching, annealing temperatures and environmental conditions) and the recording conditions, including the excitation wavelength and the incident power on the sample.' The parasitic phases, which may not be metallic, have several orders of magnitude larger scattering cross-sections. If present, even in trace amounts, these phases dominate the Raman spectra.'-' Hence most of the recently reported reliable Raman spectra have been on single crystals but over a very limited frequency range (50-800 cm-') and only on the Stokes side of the Rayleigh line.4 The higher frequency information has been derived from methods such as refle~tivity,~ electron energy loss6 and angle integrated 03774486/89/12081W)4 $05.00 zyxwvutsrqpo 0 1989 by John Wiley zyxwvutsrqpon & Sons, Ltd. photoemission7.* studies. Additional information has been derived from band structure c a l c ~ l a t i o n s . ~ ~ ' ~ We have undertaken a systematic investigation of the laser-excited Raman and optical emission spectra over a very wide spectral range (1 3 000-23 zyx OOO cm- ') on doped YBaCuO systems. Excitation frequencies were with the available discrete frequencies of the Ar + laser with special optics to lase at 528.7 nm in addition to the usual lines in the range 514.5-457.9 nm. The anti-Stokes scattering, the normal Raman scattering, the broad emission spectrum and the sharp fluorescence lines observed in the spectra are presented here for the first time for a 7.5% Dy-doped YBaCuO system. EXPERIMENTAL The samples were synthesized by the usual solid-state reaction with Y 2 0 3 , BaCO,, Dy,O, and CuO. The samples were mixed and the pellets were calcined twice at 940 and 960°C for 16 h and quenched in air with intermittent grinding. Finally, the pellets were sintered at 970°C in a flow of oxygen at a pressure of 1 bar for 12 h. The sample was cooled to 600°C and annealed at that temperature for 12 h in a flow of oxygen. Finally, the furnace was cooled to room temperature in 6 h, as described elsewhere.' 1,1 The samples were character- ized by resistivity measurements through the four-probe technique, which gave a temperature To = 96 K for the z Received 30 May 1989 Accepted 31 July 1989