Pergamon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Solid State Communications, Vol. 106. No. 6, pp. 353-356, 1998 0 1998 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038%lG98/98 $l9.OC+.oO PII: SOO38- 1098(98)00053-2 LUMINESCENCE AND STIMULATED RADIATION OF NEODYMIUM IN RARE EARTH SULPHATE CRYSTALS G. Ajith Kumar and N.V. Unnikrishnan* School of Pure & Applied Physics, MahatmaGandhi University,Kottayam-686 560, India zyxwvutsrqponmlkji (Received 22 August 1997; accepted 13 January 1998 by C.N.R. Rao) Various absorption transitions of Nd3’ ion in single crystals of neodymium sulphatehave been identifiedand their experimental oscillator strengths calculatedby numerically integrating the absorption bands. The experi- mentaloscillatorstrengths are utilised in evaluating the three phenomino- logical Judd-Ofelt intensity parameters. Variousradiative parameters such as the electric dipole linestrengths, radiative transition probabilities, radiative life times, fluorescence branching ratiosand stimulated emission cross-sections for the fluorescence transitions from 4F3,2 excited manifolds of Nd3’ ion have been evaluated. Quantumefficiency and optical gain of the most efficient 4F3,2 - 411 112 fluorescent transition have beencomputed with the help of the fluorescence data. Some informationregarding the excited state absorption intensities from the 4F312 level are also presented. 0 1998 Elsevier ScienceLtd. All rightsreserved 1. INTRODUCTION Trivalentrare earth ions activated crystals have assumed great importance because of their applicability as efficient active media in solid state lasers. A lot of experimental as well as theoretical investigations have been carried out in the past to study the spectroscopic behaviour of these ions in a variety of crystalline matrices. Among these ions, trivalent neodymium is the most promisingone because of its good fluorescence efficiency in the IR region. Optical amplificationfrom Nd3+ was first observed in single crystals of CaW04 [ 11. After that laser action have been observedin a number of Nd”+ doped crystals. A detailed discussion of the spectroscopic studies on these crystals has been reported elsewhere [2]. Cascales et al. [3] have studied the fluorescence properties of Nd”+ ion in NdTedO I I. Among thesecrystals Nd : Y~AlsO12 (YAG) is the most practical and widely used rare earth doped crystalline laser material.Van Uitert et al. [4] have grown small singlecrystals of rare earth tungstates, ortho aluminates, oxides and studied their absorption and emission properties with particular emphasis on the energy * Author to whom all correspondence should be addressed. transfer mechanismbetweenthe rare earth ions. Some of the recent investigationsin this area include the spectroscopic study of BaYzFa : Nd’+ [5], YV04 [6], LiNb04, LiTa and MgO : LiNb03 single crystals[7]. Here, we report the preparation and optical characterisation of Nd’+ ion in the rare earth sulphate crystalmatrixwith specialemphasis on its laser emissioncharacteristics. 2. EXPERIMENTAL Neodymium sulphate crystal was prepared by mixing appropriateamount of neodymium oxide and dilute sulphuric acid. Calculated quantity of neodymium oxide was mixed with appropriatevolume of dilute sulphuric acid and the resulting solutionwas evaporated at 75°C until the crystals are formed. The crystalswere then heated at 120°C to remove excess water. The crystallinity of the grown sample was confirmed by recording the X-ray diffractionpattern. The refractive index (n) of the crystal was measured with an Abbe refractometer. The density (p) of the sample was determined at room temperature by the Archemede’s principle on a sensitive microbalance. The Nd”+ ion concentration, (N) was determined from the chemical composition and the density of the crystal.Knowing the ionic concentration, the inter-ionic separation (ri) and the ionic radius (T,,) can be obtained 353