Uniform β-NaYF(4):Er(3+)/Yb(3+) hexagonal nanoplatelets were synthesized via a modified hydrothermal route, and the nanoplatelets were applied as an external, bifunctional layer in a novel DSC configuration consisting of only one internal TiO(2) transparent layer. Approximately 10% enhancements of photocurrent and overall DSC efficiency are demonstrated by the addition of the external layer, which exhibits two functions of light reflecting and near-infrared (NIR) light harvesting. The novel DSC configuration not only simplifies the DSC fabrication process but also eliminates charge recombination induced by the conducting up-converting nanocrystals when used internally thus opening the path for other more efficient up-converting nanocrystals to be designed and applied.

Three crystalline ferric arsenate phases: (1) scorodite; FeAsO 4 ·2H 2 O, (2) ferric arsenate sub-hydrate (FAsH; FeAsO 4 ·0.75H 2 O) and (3) basic ferric arsenate sulfate (BFAS; Fe[(AsO 4 ) 1−x (SO 4 ) x (OH) x ]·wH 2 O) synthesized by hydrothermal precipitation (175-225 • C) from Fe(III)-AsO 4 3− -SO 4 2− solutions have been investigated via Raman and infrared spectroscopies. The spectroscopic nature of these high-temperature Fe(III)-AsO 43− -SO 4 2− phases has not been extensively studied despite their importance to the hydrometallurgical industrial processing of precious metal (Au and Cu) arsenic sulfidic ores. It was found that scorodite, FAsH and BFAS all gave rise to very distinct arsenate, sulfate and hydroxyl vibrations. In scorodite and FAsH, the distribution of the internal arsenate modes was found to be distinct, with the factor effect being more predominant in the crystal system. For the crystallographically unknown BFAS phase, vibrational spectroscopy was used to monitor the arsenate ↔ sulfate solid solution behavior that occurs in this phase where the molecular symmetry of arsenate and sulfate in the crystal structure is reduced from an ideal T d to a distorted T d or C 2 /C 2v symmetry. With the new collected vibrational data of the pure phases, the use of attenuated total reflectance infrared (ATR-IR) spectroscopy was finally extended to investigate the nature of the arsenate in an industrial residue generated by pressure oxidation of a gold ore, where it was found that the arsenate was present in the form of BFAS.

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The Raman spectra of synthetic compounds equivalent to the variscite group: FeAsO 4 ·2H 2 O AlAsO 4 ·2H 2 O, GaAsO 4 ·2H 2 O, and InAsO 4 ·2H 2 O are reported. In particular, upon comparison of FeAsO 4 ·2H 2 O to AlAsO 4 ·2H 2 O, it is observed that the Type II (weak) H-bond lengths in the latter are slightly longer, which is postulated to affect the stability (As release) in water at pH 5 and 7. Arsenate stretching and bending vibrations were found to be distinct in terms of spectral structure and therefore well suited for fingerprinting. The calculated As-O bond strengths from existing crystallographic data showed no significant variations. The strongest ν 1 (AsO 4 3− ) stretch was used to monitor the As-O bonding interactions in the four As-O-M units, where a shift of 114 cm −1 was observed in the order FeAsO 4 ·2H 2 O (lowest) < InAsO 4 ·2H 2 O < GaAsO 4 ·2H 2 O < AlAsO 4 ·2H 2 O (highest); this order also followed exactly the measured arsenic release of these phases. This shift in ν 1 (AsO 4 3− ) position was rationalized to stem from the differences in the electronegativities of the M 3+ cations. The trends mentioned above were verified and found to also hold for the isostructural phosphate analogues strengite (FePO 4 ·2H 2 O) and variscite (AlPO 4 ·2H 2 O) using published data. Therefore, it is postulated that, as observed with the stability of solution complexes, there may be a correlation between the electronegativity of the M 3+ cation in these isostructural phases and their stability (As or P release) in water.

The nature of synthetic basic ferric arsenate sulfate (Fe(AsO 4 ) 12x (SO 4 ) x (OH) x ) and basic ferric sulfate (FeOHSO 4 ): their crystallographic, molecular and electronic structure with applications in the environment and energy3

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