Optical and IR study of Li2O–CuO–P2O5 glasses

Abstract

Infrared (IR) and UV spectra of ternary Li2O–CuO–P2O5 glasses in two series Li2O(65−X)%–CuO(X%)–P2O5(35%), X = 20, 30, 40 and Li2O(55−X)%–CuO(X%)–P2O5(45%), X = (10, 20, 30) were studied. Infrared (IR) investigations showed the metaphosphate and pyrophosphate structures and with increase of CuO content in metaphosphate glass, the skeleton of metaphosphate chains is gradually broken into short phosphate groups such as pyrophosphate. IR spectra showed one band at about 1,220 and 1,260 cm−1 for P2O5(35%) and P2O5(45%) series, respectively, assigned to P=O bonds. For CuO additions ≤20 mol%, the glasses exhibit two bands in the frequency range 780–720 cm−1 which are attributed to the presence of two P–O–P bridges in metaphosphate chain. But for CuO addition ≥30 mol%, the glasses exhibit only a single band at 760 cm−1 which is assigned to the P–O–P linkage in pyrophosphate group. In optical investigations, absorption coefficient versus photon energy showed three regions: low energy side, Urbach absorption, and high energy side. In Urbach’s region, absorption coefficient depends exponentially on the photon energy. At high energy region, optical gap was calculated and investigations showed indirect transition in compounds and decreases in optical gap with increases of copper oxides contents that is because of electronic transitions and increasing of nonbridging oxygen content.