Structure and optical properties of the Tb3+-doped antimony borate glasses.

Despite the extensive research conducted on the antimony borate glasses, further investigation is required to explore their structural characteristics when Sb2O3 replaces B2O3 in the presence of rare-earth metal oxide. Herein, the structure and properties of xSb2O3·(99-x)B2O3·1Tb4O7 (30 ≤ x ≤ 70 mol%) were investigated. The infrared (IR) spectra exhibited that there is a remarkable increase in the relative area of the absorption 800–1200 cm−1 region. This is associated with nearly constant density values, despite the heavier Sb2O3 replacing the lighter B2O3. While the molar volume is decreased with the Sb2O3 content, the oxygen packing density is decreased. These findings are related to the structural units belonging to Sb2O3. The type of these units depends on the oxidation of Sb3+ into Sb5+ through the supply of oxygen atoms from the surroundings at high melting temperatures. While Sb3+ acts as a glass network former ion through the formation of [SbO3E] and/or [SbO4E−] (where E is the 5s2 lone-pair of electrons), Sb5+ acts as a modifier ion to convert [SbO3E] into [SbO4E−] units through the formation of [SbO6], similarly to the conversion of [BO3] into [BO4̅] in B2O3 glasses. These structural units are likely contributing to the FTIR absorption 800–1200 cm−1 region, such that its relative area is considered to be the sum of the four-coordinated B atoms [BO4−] (N4) and four-coordinated Sb atoms [SbO4E−] (Sb4). These negative units compensate for the positive terbium ions (Tb3+), thus generating single-doped green phosphor for light-emitting-diode (LED) applications. [ABSTRACT FROM AUTHOR]