Photoluminescence and spectral performance of manganese ions in zinc phosphate and barium phosphate host glasses

Abstract

Zinc and barium metaphosphate glasses containing dopants of MnO2 (2, 4, 8%) were prepared. Collective studies were carried out through optical, photoluminescence and Fourier transform infrared (FTIR) spectral measurements for the prepared glasses before and after gamma irradiation. Electron spin resonance (ESR), thermal expansion and crystallization studies were also investigated. Optical spectra for undoped and MnO2–glasses reveal strong ultraviolet (UV) absorption due to trace iron impurity in the materials used for preparation of glasses and Mn2+ ions are not identified due to spin–forbidden nature of their spectra. Upon gamma irradiation, the MnO2–doped glasses reveal extension of the UV absorption exhibiting two peaks together with the generation of an induced broad visible band centered at 570–580nm. Extra two glasses doped with 8% MnO2 were melted under reducing condition and they showed characteristic band at 410nm related to Mn2+ ions absorption. Photoluminescence (PL) spectra reveal two excitation peaks in MnO2–doped zinc phosphate glasses at 348 and a sharp peak at 410nm while the MnO2–doped barium phosphate glasses exhibit a sharp peak at 410nm and a curvature at 348nm. The emission spectra show a broad band centered at 620nm in both glasses but with a curvature at 605–610nm in zinc phosphate glasses which are correlated with the transition 4T1g→6A1g.The efficiency of the photoluminescence increases with the MnO2 content and the heat treatment. The values of the optical band gap (Eopt) and Urbach energy (∆E) were calculated. FTIR spectra reveal vibrational bands due to phosphate network mainly of metaphosphate groups but in zinc phosphate glasses, the mid spectra show compact network because of the ability of Zn2+ ions to participate partly as ZnO4 or P–O–Zn linkages. Thermal expansion data show different responses. Zinc phosphate glasses show anomalous behavior related to the change in the coordination of zinc cations while barium phosphate glasses exhibit normal expansion because Ba2+ ions exist only as modifiers. The crystallization behavior reflects also anomalous behavior. The zinc phosphate glass crystallizes in two crystalline species, mainly zinc metaphosphate phase and another zinc phosphate (3ZnO·P2O5) phase while the barium phosphate glass crystallizes only in barium metaphosphate phase.