Structural properties and visible emission of Eu3+-activated SiO2–ZnO–TiO2 powders prepared by a soft chemical process

Abstract

In this work, the structural and optical properties of the 60SiO 2 e20ZnOe20TiO 2 system (in mol%) doped with 1 mol% of Eu 3þ were evaluated. Stable and transparent sols, homogeneous gels, and powders were prepared by a soft chemical process followed by annealing from 700 to 1100 C. Visible emission was observed in the photoluminescence (PL) spectra from 570 to 700 nm owing to the Eu 3þ ions, with the most intense emission peaks at 614 and 590 nm related to the 5 D 0 / 7 F 2 and 5 D 0 / 7 F 1 transitions, corresponding to red (R) and orange (O) colors, respectively. The R/O intensity ratios between 3.16 and 3.73 were observed and correlated to the structural properties of the host. X-ray diffraction patterns indicated that the reduction of PL at 614 nm and changes in the R/O values were due to the crystallization process. In addition, the FTIR spectra showed a gradual decrease of the hydroxyl absorption bands around 3436 and 1640 cm À1 and an increase of the bands related to TieOeTi and SieOeSi linkages, indicating polymerization and densification process of the host was achieved above 700 C. Moreover, increasing the annealing temperature resulted in the formation of ZnTiO 3 and Zn 2 TiO 4 crystalline phases, as well as rutile TiO 2. Finally, intensity parameters (U l), and quantum efficiency were calculated by applying JuddeOfelt theory to Eu 3þ ions, which showed that the Eu 3þ-doped samples can be used in displays and LEDs.

Structural and spectroscopic properties of Eu3+ doped Y4Al2O9 compounds through a soft chemical process

“…5). To calculate the average lifetime (τ ave ) value of the 5 D 0 excited state, we integrated the decay curve using the equation: [20]…”

“…However, for powdered samples, we cannot measure absorption coefficient and make traditional Judd-Ofelt calculations. Nevertheless, using the procedure described below, Werts and collaborators [39] and Carlos and colleagues [40] calculated the spontaneous emission probability (A), radiative lifetime (τ Rad ), quantum efficiency for 5 D 0 → 7 F 2 emission, and Ω 2 and Ω 4 parameters and already that the procedure had been used for other Eu 3+ doped materials [20,34].…”

“…The pure magnetic-dipole character of the 5 D 0 → 7 F 1 transition enables the determination of the intensity parameters from the emission spectrum. As this transition does not depend on the local ligand field experienced by Eu 3+ ions, it can be used as a reference for the entire spectrum 20,34,39,40]. The A 01 spontaneous decay rate for the 5 D 0 → 7 F 1 transition is A 01 = A′ 01 •n 3 , where A′ 01 = 14.65 s −1 in vacuum and n is the refractive index of the host material.…”

“…The branching ratio for the 5 D 0 → 7 F 5,6 transitions must be neglected owing to its low relative intensity, and the radiative contribution can be calculated using only the 5 D 0 → 7 F 0-4 transitions [20,34,40].…”

“…The great interest on the optical properties of YAM is related to its multisite structure. Normally, Eu 3+ ions can be used as structural probes and as red/orange emitters for displays [7,16,20]. The study of occupation sites is vital to understanding the photoluminescent features and the ion-ion interaction mechanisms that lead to photoluminescence quenching.…”