Journal of Luminescence 94–95 (2001) 743–746 Intrinsic localized vibrational modes in a highly nonlinear halogen-bridged metal K. Kisoda a, *, N. Kimura a , H. Harima b , K. Takenouchi c , M. Nakajima d a Department of Science Educations, Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan b Department of Electronics and Information Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan c Department of Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan d Research center for superconductor photonics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Abstract Intrinsic localized vibrational modes in a halogen-bridged Pt complex were studied by Raman spectroscopy. We compared the peak frequency of the overtone of Pt–Cl stretch vibration between that excited by an Ar þ and that by a near infrared (NIR) lasers. The decrease in the overtone peak frequency of the NIR excitation were larger than that of the visible excitation. We interpreted that the charge transfer led to weaken the bond strength and that the anharmonicity of the system became weak. r 2001 Elsevier Science B.V. All rights reserved. PACS: 63.20Pw; 78.30.Hv; 63.20Kr; 63.20Ry; 63.33.+m Keywords: Intrinsic localized vibrational mode; Anharmonicity; Charge transfer 1. Introduction If both nonlinearity and discreteness are satisfied with appropriate strength in a crystal, intrinsic localized vibrational modes (ILVMs) are supposed to appear [1–3]. ILVMs are solitonlike excitations and have been extensively studied from theoretical point of view [4,5]. In the late 1990s, however, experimental studies of ILVMs have emerged [6–9]. There is also a theoretical proposal to excite ILVMs in a perfect real crystal by irradiation of ultrashort light pulses [10]. Halogen bridged mixed valence metal com- plexes (HMMCs) ½MðAAÞ 2 ½MðAAÞ 2 X 2 Y 4 ; where M ¼ Pt; Pd, Ni; AA ¼ enðethylenediamineÞ; etc.; X ¼ Cl; Br, I; Y ¼ ClO 4 ; BF 4 ; etc., consist of linear chains of metal and halogen ions arranged alternatively. Since the interchain distance is relatively large, the coupling between the chains is sufficiently weak. Therefore, one can regard the HMMCs as a typical quasi-one-dimen- sional system. We take up the HMMC, metal being platinum (Pt) and halogen being chlorine (Cl), because the intrachain inter- action of chlorine bridged complexes is the strongest among them. Owing to the strong intrachain interaction, one can expect that ILVMs are present in this complex. Moreover, Kiselev et al. [11,12] showed numerically that *Corresponding author. E-mail address: kisoda@center.wakayama-u.ac.jp (K. Kisoda). 0022-2313/01/$-see front matter r 2001 Elsevier Science B.V. All rights reserved. PII:S0022-2313(01)00380-5