Anomalous Thermal Behavior of CuxMg1-xNb2O6 (x=0,0.4,0.6,1) for LTCC Substrate
LTCC (Low Temperature Co-fired Ceramics) being the most advantageous technology towards the multilayer substrates for various applications, demands an extensive study of its raw materials. In the present work, a series of CuxMg1-xNb2O6 (x=0,0.4,0.6,1) has been prepared using sol-gel synthesis route and sintered at a temperature of 900°C to study its applicability for LTCC technology as the firing temperature is 900°C in this technology. The phase formation has been confirmed using X-ray Diffraction. Thermal properties like thermal conductivity and thermal expansion being very important aspect as the former defines the heat flow to avoid thermal instability in layers and the later provides the dimensional congruency of the dielectric material and the conductors, are studied here over high temperature up to the firing temperature. Although the values are quite satisfactory from substrate requirement point view, results have shown anomaly over temperature. The anomalous thermal behavior has been further analyzed using TGDTA. Keywords—Niobates, LTCC, Thermal conductivity, Thermal expansion, TG-DTA.
Luminescent and structural properties of MgNb2O6 nanocrystals
Abstract This study investigated the synthesis and luminescence properties of MgNb2O6 nanocrystals by citric gel process. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence (PL). The PL spectra excited at 270 nm had a broad and strong blue emission band maximum at 450 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO6]7−. The optical absorption spectra of the 800 °C sample exhibited the band-gap energy of 3.6 eV. Furthermore, the microstructure and luminescence spectra of the products were investigated.
Li-doping effect on enhancement of photoluminescence in Gd2O3:Eu3+ films
Abstract Luminous properties of Gd 2 O 3 :Eu 3+ and Li-doped Gd 2 O 3 :Eu 3+ thin films were investigated by time resolved laser spectroscopy in the temperature range of 12–295 K. The films were grown by pulsed laser deposition method on Al 2 O 3 (0 0 0 1) substrates under different substrate temperature and oxygen pressures. Both cubic and monoclinic crystalline structures were observed in Gd 2 O 3 :Eu 3+ films, but only the cubic crystalline structure was observed for Li-doped Gd 2 O 3 :Eu 3+ films grown under certain conditions. The enhanced photoluminescence brightness by Li-doping results from the improved crystallinity and reduced internal reflections caused by rougher surfaces. Comparing to Gd 2 O 3 :Eu 3+ films, the brightness of Li-doped Gd 2 O 3 :Eu 3+ films was increased by a factor of 1.5 and 2.3 at 12, and 295 K, respectively. In this paper, it is suggested that the highest optical phonon energy of Li 2 O introduced Li to Gd 2 O 3 :Eu 3+ is another important factor for the improved luminescence brightness at high temperature. Exciting the Gd 2 O 3 :Eu 3+ films at its band gap or higher energy level of Eu 3+ ions with 266 nm excitation results in cascading multi-phonon relaxation to the emitting state of Eu 3+ ions ( 5 D 0 ), then luminescence of Eu 3+ ions takes place. The optical phonon having the highest energy plays an important role in multi-phonon relaxation process. The photoluminescence intensity was increased with increasing temperature under 266 nm excitation.