UV–visible and infrared absorption spectra of gamma irradiated V₂O₅-doped in sodium phosphate, lead phosphate, zinc phosphate glasses: A comparative study

Abstract

Radiation-induced defects generated by successive gamma irradiation have been investigated in V₂O₅-doped phosphate glasses of three basic compositions, namely, sodium metaphosphate, lead metaphosphate and zinc metaphosphate. Glasses were prepared from chemically pure materials. Melting was carried at 900°–1100 °C for 1 h and with several stirrings of the melt to achieve homogeneity. The glassy samples were annealed at 200°–250 °C and left to cool to room temperature at a rate of 20 °C/h. Polished samples from undoped and V-doped samples of equal thickness. ~ 2 mm were measured in a double beam UV–visible spectrophotometer at 200–1000 nm before and after gamma irradiation. Induced defects were analyzed for these three phosphate glass systems. Infrared absorption spectra were measured for the prepared undoped and V-doped samples by the KBr technique before irradiation and after being subjected to a high dose of 7 M Rads (7 × 10⁴ Gy). The cumulative effects of gamma irradiation on the UV–visible spectra are correlated with the intrinsic and extrinsic defects within the various three glasses. Some shielding behavior for the various glasses towards successive gamma irradiation are observed and realized in relation to the different partner anions studied. The effect of gamma irradiation on IR spectra indicates the persistence of the main characteristic bands due to phosphate network and the minor changes are correlated with the possible changes in the bond lengths and/or bond angles of the building units during the irradiation process. The effect of V₂O₅ on the IR spectra is correlated with the depolymerization effect of the glass network.

Introduction

Glasses containing transition metal ions (TMs ions) have interesting optical and electrical properties, which are due to the presence of such transition metal ions in several oxidation or coordination states in the glassy matrix [1], [2], [3], [4], [5], [6]. Vanadium as one of the TMs, can exist in glasses in three possible oxidation forms, namely, the trivalent, tetravalent, and the pentavalent states. V₂O₅ can be incorporated in glasses especially within phosphate glasses with a large percent [reaching ~ 95%] and exhibits interesting semi conducting and magnetic properties [7], [8], [9]. Spectroscopic investigations have shown that [6], [7], [8], [9], [10], [11] the trivalent greenish vanadium ions normally exist in distorted octahedral coordination with oxygens and exhibit two characteristic absorption bands at 350–400 nm [3.54–2.69 eV], and 580–680 nm [2.13–1.82 eV] and a third possible band in the UV region originating from the electron transfer within the vanadium ion itself. The tetravalent bluish vanadium ions are assumed to exist as vanadyl ions [VO²⁺] and exhibit characteristic four weak bands at about 420 nm [2.95 eV], 760–860 nm [1.63–1.44 eV] and ~ 1000 nm [~ 1.239 eV] in addition to a possible UV band. The pentavalent colorless vanadium ions correspond to the d° configuration and thus will not give rise to d–d transitions but give a characteristic charge transfer band at ~ 380 nm. The ratio of each valence of vanadium ions in a glass generally depends on the type and composition of the respective glass and melting conditions.

It has been established that vanadium ions in phosphate glasses [2], [9], [10] occur mostly in the lower valence states: V³⁺ and V⁴⁺, while in alkali borate, cabal, and borosilicate glasses [3], [4], [5], [6], the pentavalent V⁵⁺ ions are predominant. Gamma irradiation of glasses has been shown to give rise to induced optical absorption bands [12], [13]. The induced defects generated by gamma irradiation virtually originate from intrinsic defects within the glass matrix itself and from the sharing of extrinsic defects due to dopants or impurities [14], [15].

The main objective of this work is to investigate the UV–visible optical spectra of vanadium ions in three specific and different metaphosphate glasses: namely, sodium metaphosphate, lead metaphosphate, zinc metaphosphate glasses before and after gamma irradiation. A second objective of the present paper is to measure the infrared absorption spectra of the prepared undoped and V₂O₅-doped samples before and after being subjected to a high gamma dose of 7 M Rads = 7 × 10⁴ Gy.