Structure study of MoO3-ZnO-B2O3 glasses by Raman spectroscopy and formation of α-ZnMoO4 nanocrystals

Molybdenum oxide (MoO₃)-containing glasses of xMoO₃-50ZnO-(50−x)B₂O₃ (x = 10, 20, and 30) are prepared using a conventional melt quenching method, and the glass structure and crystallization behaviour are clarified. It is found that the thermal stability against crystallization of the glasses decreases drastically with increasing MoO₃ content. The main valence of Mo ions in the glasses is found to be Mo⁶⁺ from X-ray photoelectron spectroscopy measurements. The Raman bands observed at ∼860 cm⁻¹ and 950 cm⁻¹ suggest that the coordination state of Mo⁶⁺ ions in the glasses is mainly (MoO₄)²⁻ tetrahedral units. All glasses examined in this study give the formation of α-ZnMoO₄ as the initial crystalline phase. In particular, 30MoO₃-50ZnO-20B₂O₃ glass shows the bulk crystallization of α-ZnMoO₄ nanocrystals with a diameter of ∼5 nm. The crystallized glasses consisting of Eu³⁺-doped ZnMoO₄ crystals are synthesized, and enhanced photoluminescence emissions (i.e., the quantum yield is 9%) due to the 4f transitions ⁵D₀ → ⁷F_J (J = 0-4) of Eu³⁺ ions is observed.