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November 9, 2023 September 9, 2026

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

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Research article

E. Segura-Sanchis, A. Moreno, F. Ramiro-Manzano, R. Fenollosa, M. Feliz and P. Atienzar

Dalton Transactions 52, 17818-17825 (2023) · Published 9 November 2023

Published abstract

Octahedral molybdenum (Mo6) clusters constitute suitable building blocks for the design of promising single crystal materials in the field of optoelectronics. Here, we prepared single crystals composed of hydroxo Mo6X8 (X = Br, Cl) cluster complexes interconnected by H-bonding interactions with water molecules and protons. The optoelectronic responses and the absorption and emission spectra of these cluster-based single crystals were acquired upon light irradiation, and they show dependency on the nature of the halogens, with the brominated cluster being the most conductive. A fast photoelectrical response was recorded and it showed remarkable stability after multiple illumination on/off cycles. The results obtained provide relevant information for the development of photonic and optoelectronic devices, sensors and photocatalysts.

Figures

Schematic representation of hydrogen bonding in layers of the MoBr structure
Figure 1. Summary. Diagram showing H-bonding (dotted lines) in the layers of the MoBr structure (atom color code: Mo in blue, Br in green and O in red). H atoms are omitted for clarity.

Source: E. Segura-Sanchis et al., Dalton Transactions 52, 17818-17825 (2023), CC BY-NC 4.0.

Optical absorption and emission
Figure 2. Summary. (a) Diffuse reflectance and (b) steady state PL of a collection of MoBr (black line) and MoCl (red line) single crystals, registered at λexc = 405 nm under room conditions. The inset shows the time-resolved PL monitored at 720 nm.

Source: E. Segura-Sanchis et al., Dalton Transactions 52, 17818-17825 (2023), CC BY-NC 4.0.

Photoluminescence and lifetime
Figure 3. Summary. Panel a shows the probe-tip contact used to measure an individual octahedral molybdenum cluster crystal on an indium tin oxide substrate. In panel b, the MoBr crystal produces a broad photocurrent response from 400 to 550 nm with a weaker tail towards 600 nm, whereas the ionic-liquid blank remains comparatively inactive; this spectral range follows the material absorption. Panels c and d compare repeated 405 nm light on and off cycles for MoBr and MoCl, showing a stable photoresponse and the higher conductivity of the bromide crystal under illumination.

Source: E. Segura-Sanchis et al., Dalton Transactions 52, 17818-17825 (2023), CC BY-NC 4.0.

Photocurrent map, photoluminescence map, photocurrent profile and optical micrograph of a MoBr single crystal
Figure 4. Summary. (a) Photocurrent mapping of a MoBr single crystal embedded in BMIMBF4; (b) PL map of the MoBr single crystal. Both measurements were performed at room temperature with excitation using a 405 nm diode laser; (c) photocurrent profile along the dashed line depicted in (a).

Source: E. Segura-Sanchis et al., Dalton Transactions 52, 17818-17825 (2023), CC BY-NC 4.0.

Article access and reuse

This article is published under the Creative Commons Attribution-NonCommercial 4.0 licence. Official RSC article record · CC BY-NC 4.0 licence · RSC licences, copyright and permissions.

Related publications

Connections within F. Ramiro-Manzano's publication record, selected from shared research topics and evidence reviewed in the source papers.

Figure 1. Schematic representation of the electric contact on the microcrystalline samples, showing the irradiation objective at the bottom part controlled with a piezoelectric stage.
Journal article
Nanomaterials 13, 2570 (2023)
Scanning Photocurrent Microscopy in Single Crystal Multidimensional Hybrid Lead Bromide Perovskites
E. Segura-Sanchis, R. García-Aboal, R. Fenollosa, F. Ramiro-Manzano and P. Atienzar

What the related paper adds

This paper complements Optoelectronic properties of octahedral molybdenum cluster-based materials at a single crystal level within the same research line. This study moves from optical resonances to spatially resolved charge transport in individual lead-bromide perovskite crystals. Scanning photocurrent microscopy separates the two transport regimes found in three-dimensional crystals from the single dominant regime in multidimensional 2D-3D crystals and exposes crystal edges as important recombination regions.

What this paper adds to the related work

Alongside Scanning Photocurrent Microscopy in Single Crystal Multidimensional Hybrid Lead Bromide Perovskites, this paper develops a complementary part of the problem. This paper characterizes hydrated molybdenum cluster single crystals as optically active and electrically responsive microstructures. Their size- and orientation-dependent photoluminescence, visible photocurrent and Fabry-Perot behaviour extend single-crystal cavity and transport measurements beyond lead-halide perovskites to a distinct cluster-based material family.

Figure 4: MAPbBr3 crystal optical properties
Article
Dalton Trans. 49(36), 12798-12804 (2020)
Optical Properties of Organic/Inorganic Perovskite Microcrystals through the Characterization of Fabry-Pérot Resonances
F. Ramiro-Manzano, R. García-Aboal, R. Fenollosa, S. Biasi, I. Rodriguez, P. Atienzar and F. Meseguer

What the related paper adds

This earlier paper establishes a scientific basis for Optoelectronic properties of octahedral molybdenum cluster-based materials at a single crystal level. This work uses the Fabry-Perot fringes of individual MAPbBr3 microcrystals as a source of quantitative information. A simultaneous fit of transmittance and photoluminescence retrieves crystal thickness and the real and imaginary parts of the refractive index near the band edge, while defining when a planar microcrystal behaves as an optical cavity.

What this paper adds to the related work

Building on the earlier contribution Optical Properties of Organic/Inorganic Perovskite Microcrystals through the Characterization of Fabry-Pérot Resonances, this paper advances the research line. This paper characterizes hydrated molybdenum cluster single crystals as optically active and electrically responsive microstructures. Their size- and orientation-dependent photoluminescence, visible photocurrent and Fabry-Perot behaviour extend single-crystal cavity and transport measurements beyond lead-halide perovskites to a distinct cluster-based material family.

Research fields

Bottom-up

Aquahydroxo molybdenum-cluster single crystals containing chloride or bromide ligands are grown from alkaline aqueous solutions. Their hydrogen-bonded crystal network makes it possible to study cluster-derived optical and electrical behaviour without averaging over a powder or composite film.

Simulations & fits

The crystal dimensions and refractive response are interpreted through a Fabry-Pérot cavity model. This identifies the larger bromide crystals as optical microresonators and distinguishes cavity fringes from the intrinsic cluster photoluminescence.

Characterization

Diffuse reflectance, steady-state and time-resolved photoluminescence, wavelength-resolved photocurrent and spatial photocurrent maps are measured on individual crystals. The maps compare local carrier collection with emission and reveal the effect of the electrical probe contact across a single specimen.

RESEARCH TOPICS

EmissionBoth cluster crystals emit in the red/near-infrared from the triplet state of the {Mo6X8}4+ core after intersystem crossing. The comparison shows why spectral colour alone is insufficient to characterise how halogen substitution changes excited-state dynamics.MaterialsMeasurements are performed at single-crystal scale to exclude grain-boundary and amorphous-domain contributions present in pressed powders or polycrystalline films. Current-time traces under 405 nm illumination remain repeatable over multiple on/off cycles, showing that the photoresponse is a property of the crystal rather than an irreversible charging artefact.ChemistryMoCl and MoBr retain comparable octahedral Mo6 cluster frameworks while changing the inner halogen. Figure 1 shows clusters connected into layers by hydrogen bonding to water molecules and protons.
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