Spectrochimica Acta Part A 60 (2004) 933–939 Laser photoacoustic spectra of Sm 3+ ion in Sm 2 O 3 and SmCl 3 ·6H 2 O in the spectral profile 484–542 nm B. Mandal a,∗ , S.N. Thakur b a Department of Physics, Sonamukhi College, Sonamukhi, Bankura 722207, India b Laser and Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi 221005, India Received 29 April 2003; received in revised form 23 June 2003; accepted 23 June 2003 Abstract Microphone based photoacoustic (PA) spectrometer to study solids in powder form was designed and fabricated. Laser PA spectra of Sm 3+ ion in Sm 2 O 3 and SmCl 3 ·6H 2 O microcrystalline powders were recorded first time in 484–542 nm spectral region at room temperature. Analysis of these PA spectra shows new information on the Stark components of ground and excited states of Sm 3+ ion. A comparison of Stark energy levels of Sm 3+ ion in both oxide and hexahydrated chloride hosts is presented here. © 2003 Elsevier B.V. All rights reserved. Keywords: Photoacoustic spectroscopy; Sm 2 O 3 ; SmCl 3 ·6H 2 O; Stark components; Microphone detector 1. Introduction Intermediate phase reaction study [1] of rare earth oxides and usefulness of rare earth ions in laser materials, optical fiber etc. have attracted considerable attention in high resolu- tion spectroscopy of rare earth ions in various host material [2]. Sm 3+ ion in oxide [2] and hexahydrated chloride matri- ces is one of the rare earth ions that does not give response well in conventional spectroscopic technique especially in blue–green region [3,4]. This implies that the non-radiative decay process plays vital role in the transitions involved in Sm 2 O 3 and SmCl 3 ·6H 2 O matrices. The PA effect, invented by Bell [5], is the process of acoustic wave generation in a sample resulting from the ab- sorption of photons. The important advantage, which leads this type of technique to become very popular is that no sample preparation is required. Another advantage is that it serves very well in the case of very low absorbing materi- als. Presently, PZT based photoacoustic detection technique is commonly used to study solid materials due to the better impedance matching between sample and detector rather than a microphone based PA detection technique [6]. But PZT is of two orders of magnitude less sensitive than micro- phone [4,6]. So a sensitive microphone can eliminate this pr- oblem though it shows very less impedance matching factor. ∗ Corresponding author. Systematic studies of PA spectra of Sm 3+ ion in oxide host were reported earlier [3,7,8] but all these are in low resolution. PA study of Sm 3+ ion in SmCl 3 ·6H 2 O is not reported so far. So further studies on Sm 3+ ion in oxide and hexahydrated chloride hosts are necessary to get more information regarding Stark energy levels of ground and excited states in Sm 3+ ion in crystal field. A home made PA spectrometer was employed to record the PA spectra of Sm 3+ ion in Sm 2 O 3 and SmCl 3 ·6H 2 O crystalline powders at room temperature. 2. Instrumentation 2.1. Light source We used the third harmonic radiation (355 nm) from a Nd:YAG (quanta Ray DCR-2A) laser with a pulse dura- tion ∼7 ns and energy per pulse ∼100 mJ to pump the dye laser (Quanta Ray PDL-2). The dye used to cover spectral range 484–542 nm was Coumarin 500. Bandwidth of the dye laser was 0.05 nm. The dye laser output was in the order of 4 mJ/pulse. 2.2. PA cell The PA cell in its simplest form, was an enclosed cham- ber containing sample, a microphone, a non absorbing cou- 1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00322-6