Glass‐Ceramics Based on β‐Quartz and β‐Spodumene Solid Solutions Nucleated by (Tm ³⁺ ,Yb ³⁺ ):YNbO ₄

ABSTRACT

The glass of the lithium aluminosilicate (LAS) system doped with yttrium, thulium, ytterbium, and niobium oxides was melted at 1580°C and heat‐treated at 720°C–1350°C. DSC, XRD, SEM, Raman and optical spectroscopy were used to study structure, morphology, and spectral‐luminescent properties of these materials. Orthorhombic (T′), tetragonal (T), and monoclinic (M) (Tm ³⁺ ,Yb ³⁺ ):YNbO ₄ nanocrystals with sizes increasing from 8 to 25 nm consistently appear and grow with increasing the heat‐treatment temperature. Their absorption and up‐conversion luminescence properties significantly change following appearance and phase transformations of (Tm ³⁺ ,Yb ³⁺ ):YNbO ₄ nanocrystals. (Tm ³⁺ ,Yb ³⁺ ):YNbO ₄ nanocrystals serve the nucleating agent for the main crystalline phase, β‐quartz solid solutions (ss), with size of 48 nm, which appears during heat treatment at 800°C and begins to transform into β‐spodumene ss at 1150°C. Due to crystallization of β‐quartz ss, transparent glass‐ceramics have a thermal expansion coefficient close to zero, equal to (0.3–0.5) × 10 ⁻⁶ K ⁻¹ . Opaque glass‐ceramic fabricated at 1350°C contains the stable crystalline phases of M‐(Tm ³⁺ ,Yb ³⁺ ):YNbO ₄ and β‐spodumene ss. Transparent glass‐ceramic with T′‐(Tm ³⁺ ,Yb ³⁺ ):YNbO ₄ nanocrystals shows intense blue up‐conversion luminescence with a high color purity parameter. The glass‐ceramic with a mixture of the T‐ and M‐phases demonstrates the efficiency of up‐conversion energy transfer from Yb ³⁺ to Tm ³⁺ ions of 90%. It provides intense pure near‐IR Tm ³⁺ up‐conversion luminescence at ∼800 nm and is a promising near‐IR up‐conversion phosphor.