The role of network modifiers in the creation of photoluminescence in CaTiO3

• Published in: Materials chemistry and physics Vol. 78; no. 1; pp. 227 - 233
• Main Authors: Pontes, F.M, Pinheiro, C.D, Longo, E, Leite, E.R, de Lazaro, S.R, Varela, J.A, Pizani, P.S, Boschi, T.M, Lanciotti, F
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 03-02-2003; Elsevier
• Subjects: Absorbance spectrum; Calcium titanate; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Other solid inorganic materials; Photoluminescence; Physics; Absorbance spectrum; Photoluminescence; Calcium titanate; Absorption spectroscopy; Energy levels; Semiconductor materials; Ternary compounds; Titanates; Calcium compounds; XRD; Experimental study; Raman spectroscopy; Calcium oxides; Optical properties; Crystal structure
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/S0254-0584(02)00230-4

We discuss the nature of visible photoluminescence (PL) at room temperature in amorphous calcium titanate in the light of the results of recent experimental and quantum mechanical theoretical studies. Our investigation of the electronic structure involved the use of first-principle molecular calculations to simulate the variation of the electronic structure in the calcium titanate crystalline phase, which is known to have a direct band gap, and we also made an in-depth examination of amorphous calcium titanate. The results of our theoretical calculations of amorphous calcium titanate indicate that the formation of fivefold coordination in the amorphous system may introduce delocalized electronic levels in the highest occupied and the lowest unoccupied molecular orbitals. These delocalized electronic levels are related to the formation of a tail in the absorbance spectrum curve. The results indicate that amorphous calcium titanate has the conduction band near the band gap dominated by Ca states contribution. Experimental optical absorption measurements showed the presence of a tail. These results are interpreted by the nature of these exponential optical edges and tails, associated with defects promoted by the disordered structure of the amorphous material. We associate them with delocalized states in the band gap.