Transparent glass-ceramics with (Eu3+,Yb3+):YNbO4 nanocrystals: Crystallization, structure, optical spectroscopy and cooperative upconversion

Identifier:  PC:3331

Handle: https://hdl.handle.net/20.500.11797/PC3331

Authors:  Mateos, X.; Loiko, P.; Dymshits, O.; Alekseeva, I.; Zhilin, A.; Tsenter, M.; Vilejshikova, E.; Bogdanov, K; Yumashev, K

Abstract:
. In the present work, we report on a comprehensive study of crystallization, structure and optical spectroscopy of transparent glass-ceramics with (Eu3+,Yb3+):YNbO4 nanocrystals synthesized by a secondary heat-treatment of Li2O–Al2O3–SiO2 glasses doped with rare-earth oxides and nucle-ated by Nb2O5, for the first time, to the best of our knowledge. Heat treatments result in volume crystallization of RENbO4 with the sizes of 4 – 15 nm. Crystals of rare-earth niobates with disor-dered fluorite structure (T’) appear during heat-treatment at 720–740 °C for 6 h, crystals with tetragonal structure (T) appear at higher temperatures or longer durations of heat-treatment, and at >1000 °C the transformation to a monoclinic form (M) begins. Rare-earth niobates act as nu-cleating agents for bulk crystallization of β-quartz solid solutions, the main crystalline phase of the glass-ceramics. Optical spectroscopy confirms entering of both Eu3+ and Yb3+ ions into the RENbO4 nanophase and their specroscopic properties changes according to the T’ → T → M phase transformations. Under UV excitation, glass-ceramics heat-treated at 900 °C provide in-tense red emission with the color coordinates x = 0.665, y = 0.335 (CIE 1931). At 1000 °C, a par-tial reduction of Eu3+ to Eu2+ is observed which allows for tuning of color properties of emission. When excited in the near-IR by an InGaAs diode, the initial glass and glass-ceramics show red cooperative upconversion due to the 2Yb3+ → Eu3+ energy transfer. The efficiency of the latter is ~10%. The developed materials due to the good emission and thermo-mechanical properties are promising for the development of color-tunable red phosphors.