ISSN 0018-1439, High Energy Chemistry, 2015, Vol. 49, No. 6, pp. 438–448. © Pleiades Publishing, Ltd., 2015. 438 1 Cadmium selenide (CdSe) is an important semi- conducting material due to its potential use in photo- conductive devices and solar cells [1–4]. CdSe thin films have widely been studied because of its high ab- sorption coefficient and nearly optimum band gap en- ergy (1.73 eV). It finds a wide range of applications in low cost devices such as light emitting diodes, solar cells, photodetectors, electro photography and laser diodes [1, 4–6]. Cadmium selenide nanoparticles have different optical and electrical properties com- pared to bulk CdSe due to the strong confinement of excited electrons and holes [7]. The band gap of CdSe colloidal nanoparticles can be tuned through the con- trol of nanoparticles size to give emission from red to blue [8]. These superior properties made CdSe NPs useful for optoelectronic devices, high efficiency solar cells, nano-sensors, and biomedical applications [9]. Many methods are adapted to synthesis CdSe NPs such as chemical precipitation, chemical bath deposi- tion CBD, surfactant assisted hydrothermal, electro- chemical, laser ablation etc. [10]. Laser ablation in liq- uid is a very interesting technique due to simplicity, high purity and stability of colloids, doesn’t need cat- 1 The article is published in the original. alyst or vacuum, good control on particles size, and safe handling of colloids [11]. Up to best of our knowl- edge, few data have been published related to the laser ablation of CdSe NPs in liquid [1, 12, 13]. Recently, Sabit et al. [14] investigated the photovoltaic charac- teristics of CdSe quantum dots prepared by pulsed fre- quency quadrupled Nd:YAG laser in methanol. Re- cently we have reported that liquid type affects the properties of colloidal CdSe nanoparticles synthesized by laser ablation [15]. In this paper, we report on the effect of laser fluence on the structural, optical and electrical properties of CdSe NPs synthesised by laser ablation in methanol. EXPERIMENTAL DETAILS The laser used for the ablation is Nd:YAG operat- ing at 10 Hz repetition rate, with 7 ns pulse width and wavelength of 1064 nm. The laser pulses were focused by a 20 cm positive lens onto a cleaned 2 mm thick CdSe bulk sample (99.99% purity provided from Poch company) immersed in methanol at various laser flu- ences (1.32, 1.76, 2.12, 2.51 and 2.92 J/cm 2 ) with an ablation time of 20 min. The energy of laser pulse was measured using calibrated Joule meter after taking in- Effect of Laser Fluence on the Characteristics of CdSe Nanoparticles Prepared by Laser Ablation in Methanol 1 R. A. Ismail a , N. F. Habubi b , and A. N. Abd c a Department of Applied Sciences, University of Technology Baghdad, Iraq e-mail: raidismail@yahoo.com b Physics Department, Education Faculty, University of Al-Mustansiriyah Baghdad, Iraq c Physics Department, Science Faculty, University of Al-Mustansiriyah Baghdad, Iraq Received Jnuary 11, 2015; in final form, May 05, 2015 Abstract—The effect of laser fluence on structural, morphological, optical, and electrical properties of CdSe nanoparticles NPs prepared by irradiating a CdSe target, immersed in methanol, with Nd:YAG laser pulses at laser fluences in the range of (1.32–2.92) J/cm 2 has been studied. X-ray diffraction XRD measurements disclosed that the CdSe NPs were of wurtzite hexagonal crystal structure. Transmission electron microscopy investigation revealed that the synthesized CdSe particles are spherical and have an average particle size in the range of (37–94 nm). Scanning electron microscope SEM and transmission electron microscope TEM investigations showed that the shape and size of the synthesized CdSe NPs depend on laser fluence. The nanoparticles distribution was correlated with laser fluence. Atomic force Microscopic AFM investigations showed highly dispersed ball-shape CdSe particles. The optical energy gap of CdSe nanoparticles prepared has been determined from optical properties and found to be in the range of (1.7–2.05 eV). Optical constants of CdSe NPs were determined from transmittance and reflectance spectra. Hall measurement showed that the CdSe nanoparticles were n-type and their carrier concentration and mobility was investigated. Keywords: laser ablation, nanoparticles, colloidal, cadmium selenide, optical properties, laser fluence DOI: 10.1134/S0018143915060089 LASER CHEMISTRY