ABSTRACT
Radioluminescence and visible photoluminescence tunability features from a single Tm3+-doped yttrium tantalate phosphor prepared by a soft sol-gel method designed to afford cubic Y3TaO7 and monoclinic M'-YTaO4 crystalline phases are reported. The annealing temperature influenced the crystallization kinetics and stabilized a preferential phase. To investigate how the crystalline phase affected the Tm3+ optical properties, excitation and emission spectra in the visible range were recorded for the samples annealed at 900 or 1100 °C. Inhomogeneous broadening in the emission spectra was due to the structural disorder of the Y3TaO7 phase. Energy transfer between the yttrium tantalate host and Tm3+ ions was observed upon CT band excitation. Under UV light, an intense and tunable cyan to blue emission ascribed to both the Tm3+ transitions 1D2 â 3F4 and 1G4 â 3H6 also emerged and could be observed by the naked eye. The lifetime decay curves demonstrated the occupation of distinct sites and that the symmetry sites occupied by Tm3+ ions in the Y3TaO7 host have higher lifetime values than in the M'-YTaO4 phase. A radioluminescence study was carried out to evaluate the yttrium tantalate scintillation performance, which was considerably enhanced in the presence of the M'-YTaO4 phase. Intense white light emission displaying a large color correlated temperature range could be obtained by controlling the delay time for the time-resolved measurements and upon an orange-emitting phosphor addition. All the above-mentioned structural and photoluminescence properties make these Tm3+-doped yttrium tantalates potential candidates for photonic applications, particularly integrated w-LED systems.
ABSTRACT
This paper reports on the preparation of Er3+/Yb3+/Tm3+, Er3+/Yb3+/Nd3+, and Er3+/Tm3+/Nd3+ triply doped and Er3+-doped SiO2-Ta2O5 glass ceramic nanocomposites and active planar waveguides by the sol-gel process using the dip-coating technique as deposition method. The investigation of their structural, morphological, and luminescent properties using XRD, AFM, and photoluminescence analysis, are reported here. The XRD results showed the presence of L-Ta2O5 nanocrystals dispersed in the SiO2-based amorphous host for all the nanocomposites and films. The rare earth ion (RE3+) doping concentration affected both the crystallinity, and the crystallite sizes of the Ta2O5 dispersed into SiO2-Ta2O5 nanocomposites and waveguides. AFM characterization revealed crack free and smooth surface roughness and differences in viscoelasticity on the Er3+-doped SiO2-Ta2O5 films surface, which allows the identification of Ta2O5 nanocrystals on the SiO2 amorphous host. The Er3+ doped and triply doped SiO2-Ta2O5 nanocomposites displayed broad- and super broadband NIR emissions with a FWHM up to 173 nm achieved in the telecom wavelengths. The lifetime of the 4I13/2 emitting level of the Er3+-doped SiO2-Ta2O5 waveguides is strongly dependent on Er3+ concentration and an emission quenching was negligible up to 0.81 mol%. The structural and luminescent investigations indicated that RE3+-doped SiO2-Ta2O5 glass ceramics are promising candidates for photonic applications in optical devices operating in wide wavelengths at the telecom bands.
ABSTRACT
We report the synthesis of a Y3TaO7 solid solution containing a high Eu3+ concentration (from 7 up to 50 mol%) and investigate how Eu3+ influences the Y3TaO7 crystallization process. To this end, we evaluate the Y3TaO7 structural features and photoluminescence properties after Eu3+ introduction into the Y3TaO7 lattice. The higher the Eu3+ ion concentration, the more stable the crystallization process of the Y3TaO7 phase seems to be. The Eu3+-containing Y3TaO7 displays intense orange-reddish, broad band emission because Eu3+ occupies different symmetry sites in the host and causes inhomogeneous broadening. Eu3+ emission quenching due to Eu3+ concentration is negligible up to 30 mol% and absolute quantum yield values of up to nearly 30% were obtained, making Eu3+-containing Y3TaO7 interesting materials for application as high-intensity emitters in photonics.
