Luminescent Eu3+-doped NaLa(WO4)(MoO4) and Ba2CaMoO6 prepared by the modified Pechini method

Abstract

Modified Pechini synthesis routes were developed for synthesis of the novel red phosphor materials NaLa(WO4)(MoO4):Eu 3+ and Ba2CaMoO6:Eu 3+ . Phase pure NaLa(WO4)(MoO4):Eu 3+ was obtained at calcination temperatures ≥ 600 °C using malic acid or tartaric acid as complexing agents. Phase pure Ba2CaMoO6:Eu 3+ was attained using EDTA and citric acid, at calcination temperatures ≥ 800 °C. Choice of complexing agents were discussed on the basis of the solubility of the precursors, metal complex stability constants and conformations of the complexes. The powder properties were characterised using X-ray diffraction, thermal analysis and electron microscopy. Photoluminescence emission intensity was studied as a function of the complexing agents used and calcination temperature of the powders. Maximum emission intensity for NaLa(WO4)(MoO4):Eu 3+ was obtained at a calcination temperature of 600 °C, whereas the maximum for Ba2CaMoO6:Eu 3+ was obtained after calcination at 1100 °C. Both materials displayed desirable optical properties for use as phosphors in white light emitting diodes.

Modified Pechini Synthesis of Oxide Powders and Thin Films

“…The cation charge, cation size as well as number of valence electrons are important factors determining the acidity or basicity of cations and hence the stability of chelate complexes. For the most basic cations like Ba it has been found necessary to add EDTA as an additional complexing agent (Sletnes et al 2016). Normally the carboxylic acid like citric acid is added in excess, typically with a molar ratio citric acid:cations from 1 to 3, and this ratio is important for the success of the synthesis as will be demonstrated in some of the examples provided (Fontaine et al 2004;Nityanand et al 2011).…”

“…Normally the carboxylic acid like citric acid is added in excess, typically with a molar ratio citric acid:cations from 1 to 3, and this ratio is important for the success of the synthesis as will be demonstrated in some of the examples provided (Fontaine et al 2004;Nityanand et al 2011). The order of mixing of the cations and chelating agents has been studied in a few examples and it is normal to add the cation forming the most stable chelate first followed by the cations forming less stable chelates (Sletnes et al 2016). …”

“…The decomposition products are normally not identified and not well described in relevant literature. The spongy-like precursor material is first turned into an amorphous material that is further crystallized into a single phase target material (Tai and Lessing 1992a;Sletnes et al 2016). The crystallization temperature is dependent on the system but can be as low as 400 °C as for example in ITO (Sunde et al 2012).…”

“…In a work by Sletnes et al, NaLa(WO4)(MoO4) was synthesized by using malic and tartaric acid, with and without EG (Sletnes et al 2016). All of the syntheses yielded phase-pure materials after calcination at 600 °C, but when malic acid was used alone precipitation of a salt was observed in the gel.…”

“…Stability constants (log K) of complexes of Ca 2+ , Ba 2+ , Na + and La 3+ with malic acid, tartaric acid, citric acid, EDTA and DTPA. From (Sletnes et al 2016).…”