Gap energy studied by optical transmittance in lead iodide monocrystals grown by Bridgman's Method

Abstract

The bandgap energy as a function of temperature has been determined for lead iodide. The monocrystal was obtained in a vacuum sealed quartz ampoule inside a vertical furnace by Bridgman's method. The optical transmittance measurement enables to evaluate the values of Eg. By a fitting procedure of Eg as a function of temperature is possible to extract the parameters that govern its behavior. The variation of Eg with temperature was determined as: Eg(T) = Eg(0) - a T2/( a + T), with: Eg(0) = (2.435 ± 0.008) eV, a = (8.7 ± 1.3) x 10-4 eV/K and a = (192 ± 90) K. The bandgap energy of lead iodide at room temperature was found to be 2.277 ± 0.007 eV.