Dielectric and photoluminescent investigation of Sr3MO6 (M = W or Mo) double perovskite electroceramic

Abstract

In this work, the dielectric properties of Sr3WO6 (SWO) and Sr3MoO6 (SMO) double perovskite at radio frequencies as a function of the temperature and a study in microwaves range to evaluate the material as a novel dielectric resonator, those studies were first investigated when can be found in the second and third chapter of the thesis, respectively. Thermo-activated charge transfer process for SWO ceramic was observed and two resistor – capacitor associations were fitted for the Nyquist diagram. SWO presented negative values of temperature coefficient of capacitance (TCC) and the activation energies of dielectric relaxation processes was obtained the value around 1.3eV. For the microwave range, SWO shows high dielectric permittivity (13.57) and dielectric loss (0.0281). The temperature coefficient of resonant frequency value was first obtained in the literature. The dielectric resonator antenna (DRA) fabricated from SWO ceramic presented an operation frequency in 4.1 GHz and return loss below -40dB. For the SMO double perovskite, it was proposed an equivalent circuit using three associations of R-CPE in parallel. The SMO-based DRA operated at 3.71 GHz (frequency of operation antenna), with reasonable gain (5.00 dBi) and directivity (5.70 dBi), where these values are close to the ones presented by commercial antennas. From these results, the SWO and SMO based DRA shows good properties to be used as a novel microwave dielectric resonator. Once the first part, involving a dielectric investigation, of the doctoral thesis was concluded, the next step was to study the photoluminescence properties of SMO phosphors with Eu3+ and Tb3+ ions. The satisfactory synthesis of phosphors, the energy transfer mechanism and band emission from Eu3+, and energetic contribution of Tb3+ are in the fourth chapter. It noticed that the emission spectra of singly Eu3+ doped Sr3MoO6 phosphors consist emission transitions of 5D to 7F. The emission spectra of co-doped Tb3+ and Eu3+ doped Sr3MoO6 phosphor, there is an influence of Tb3+ ions in the energy transfer mechanism of Eu3+ ions in the phosphor. The investigation indicates that the phosphors may be a promising candidate phosphor for applications in LED chips.