Abstract
The spectroscopic properties of LaGaO3, doped with V ions, were examined in terms of the possibility of the stabilization of particular vanadium oxidation states. It was shown that three different approaches may be applied in order to control the ionic charge of vanadium, namely, charge compensation, via incorporation of Mg2+/Ca2+ ions, citric acid (CA)-assisted synthesis, with various CA concentrations and grain size tuning through annealing temperature regulation. Each of utilized method enables the significant reduction of V5+ emission band at 520 nm associated with the V4+→ O2− CT transition in respect to the 2E→ 2T2 emission band of V4+ at 645 nm and 1E2 → 3T1g emission band of V3+ at 712 nm. The most efficient V oxidation state stabilization was obtained by the use of grain size modulation, which bases on fact of different localization of the V ions of given charge in the nanoparticles. Moreover, the CA-assisted synthesis of LaGaO3:V determines V valence states but also provides significant separation of the nanograins. It was found that superior charge compensation was achieved when Mg2+ ions were introduced in the matrix, due the more efficient lability, resulting from the comparable ionic radii between Mg2+ and V ions.
Highlights
It is well-known that the electronic configuration of optically active ions and their spectroscopic properties depend strongly on the their oxidation state (Weber and Riseberg, 1971; Felice et al, 2001; Gupta et al, 2014; Matin et al, 2017; Drabik et al, 2018; Kniec and Marciniak, 2018a,b; Trejgis and Marciniak, 2018)
It was presented that three different approaches including the implementation of compensating ions, by altering the ratio of citric acid to metal ions and the tuning of the size of the nanocrystals in range 66–145 nm through change of annealing temperature in 800– 1,100◦C range may provide the ability to regulate the valence state of vanadium ions
In turn the citric acid-assisted synthesis, where CA was used in the excess in respect to total amount of metals in the lattice, leads to the significant increase of V4+ and V3+ luminescent intensity with the simultaneous improvement of nanocrystals separation and narrower size distribution in respect to the powders obtained using Pechini method
Summary
It is well-known that the electronic configuration of optically active ions and their spectroscopic properties depend strongly on the their oxidation state (Weber and Riseberg, 1971; Felice et al, 2001; Gupta et al, 2014; Matin et al, 2017; Drabik et al, 2018; Kniec and Marciniak, 2018a,b; Trejgis and Marciniak, 2018). An immense impact of synthesis method and annealing temperature on crystalline size, dispersion factor of the particles, size distribution were presented (Kniec and Marciniak, 2018a,b), which in turn lead to the presence of different V valence states, characterized by distinct luminescent properties and susceptibility to changes of local ion environment.
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