Octahedral Molybdenum Cluster-Based Single Crystals as Fabry–Pérot Microresonators

Abstract

Single crystals built up from octahedral Mo 6 cluster units, with appropriate geometry and size, constitute Fabry−Peŕottype optical microcavities with well-defined resonances. Such resonances appear in the VIS-NIR range when performing optical transmittance (OT) or photoluminescence (PL) measurements. They strongly depend on the crystal thickness and on the optical constants of the material, specifically the real and imaginary parts of the refractive index. In this work, the accurate measurement of the crystal thickness is used for the determination of the optical constants by means of a fitting process, and the preferred orientation of the crystals was determined by X-ray diffraction.

Optoelectronic properties of octahedral molybdenum cluster-based materials at a single crystal level

“…Dalton Transactions approximately on the same order of magnitude as those reported for [{Mo 6 X i 8 }X a 6 ] 2− (X i = X a = Cl, Br) crystalline compounds. 20,23 Interestingly, the emission maxima of polycrystalline MoBr (740 nm) differ from those reported previously for other samples with similar composition (670 nm), 15,21 probably related to morphological reasons that would be studied in a follow-up work. The emission spectra of single crystals (Fig.…”

“…13 Higher pH values produced a gelatinous suspension and concomitant degradation of the cluster material. Whereas the MoBr crystalline material remains stable for at least 2 years under air conditions and light radiation, 21 the Mo 6 Cl i 8 cluster material involving water and/or hydroxide groups loses water very easily. 13 It was reported previously that the exposition of MoCl to vacuum conditions for several hours promotes the dehydration of the solvation molecules, and the color of the crystals changes from yellow to orange after heating at 67–100 °C.…”

“…MoBr crystals were obtained in triethylamine/ water mixtures, following a methodology reported by us. 21 Single crystals of MoCl (≤80 µm) were grown after a slow hydrolysis reaction between [{Mo 6 Cl i 8 }Cl a 6 ] 2− and ammonium hydroxide until pH 10.0-11.5, following a similar methodology described by Sheldon. 13 Higher pH values produced a gelatinous suspension and concomitant degradation of the cluster material.…”

“…Recently, the determination of the optical properties of (H 3 O) 2 [{Mo 6 Br i 8 }(OH) a 6 ]•10H 2 O (MoBr) single crystals allowed us to identify for the first time their behavior as Fabry-Pérot microresonators. 21 This property represents a proof of concept of a photonic building block employing a Mo 6 cluster crystal. Instituto de Tecnología Química, Universitat Politècnica de València -Consejo Superior de Investigaciones Científicas (UPV-CSIC), Avd.…”

“…The MoBr, Cs 2 [{Mo 6 Cl i 8 } Cl a 6 ] and MAPbBr 3 materials were synthesized following reported procedures. 21,26,35 NH 4 OH was purchased from commercial resources (25% Supelco), as well as BMIMBF 4 ( pure, Merck), dichloromethane and acetonitrile (≥99.8% and 99.9%, respectively, Sigma Aldrich). Ultrapure deionized water was obtained from a Milli-Q® EQ 7000 Type 1 purification system.…”