Study of energy gaps and their temperature-dependent modulation in LaCrO<inf>3</inf>: A theoretical and experimental approach

In the present study, the origin of three energy gaps of lanthanum chromium oxide, one arises due to the charge-transfer gap between O-2p and Cr-3d and two arises from the d-d transitions, is analyzed in detail using the diffuse reflectance spectroscopy technique. The spin allowed transitions, such as 4T1(P)→4A24T1(F)→4A2, and 4T2→4A2, and the spin and parity forbidden 2E →4A2 transitions are depicted using a Tanabe-Sugano (T-S) diagram and an absorption spectrum. The high crystal field strength of 3.27 obtained from the T-S diagram provides high directional emission and makes the system suitable for near infrared lasing applications. Moreover, the investigations into the variation of a charge-transfer gap with temperature will provide insights into the modification of numerous optical properties toward development of optoelectronic devices. Using this temperature-dependent diffuse reflectance spectroscopy studies, we have obtained the important optical parameters, such as Urbach energy (Eu) and Urbach focus. Furthermore, first-principles calculations are carried out in order to validate the experimental findings on LaCrO3. The experimental results are in consonance with the charge-transfer gap obtained from the theoretical calculations. Furthermore, the bandgap variation with temperature is fitted using Varshni's relation, and the Debye temperature is calculated.