CrystEngComm Blog

A new red-emitting nanophosphor with potential use in white light-emitting diodes (LEDs) has recently been reported by Mi and colleagues.

White LEDs are used for lighting as they use little energy, have high brightness and long lifetimes and are considered environmentally friendly. Currently, these LEDs consist of a combination of a yellow-emitting phosphor and a blue LED chip. However, the lack of a red component is problematic, leading to a low colour rendering index (in other words, some colours do not appear naturalistic) and a high colour temperature (giving light a blue hue). Other possible methods of generating white LEDs that use red phosphors are limited by the low stability and efficiency of commercial sulphide-based red phosphors. Now, Mi and colleagues report an efficient and stable europium-based red phosphor that could solve the problem and improve the suitability of white LEDs for certain medical applications.

The phosphor Ca₉Eu(PO₄)₇ was prepared using hydrothermal methods from calcium- and europium- nitrates and phosphoric acid. It shows a red emission at 616nm under excitation at 397nm. This is attributed to the ⁵D₀ →⁷F₂ transition in Eu³⁺, which will only happen when the Eu ion occurs in sites without inversion symmetry (as it is parity forbidden).

When the phosphor was doped (in other words, when Eu was partially replaced by Gd, La or Y), the emission intensity decreased. The pH value of the synthesis reaction was found to alter the morphology of the phosphor (see the diagram below) from rods to spheres, which had different luminescence properties. The most favourable properties were obtained from rods obtained at pH 7, attributed to the smallest number of lattice defects being formed at this pH. The rods are approximately 100nm long with an aspect ratio (long axis length to width ratio) of 2.5. This phosphor shows a good colour saturation index (R = 2.4) and future studies to optimise its properties could lead to potential application in white LEDs.

For more details read the full paper at:

Hydrothermal synthesis and photoluminescence properties of Ca₉Eu(PO₄)₇ nanophosphors
Jiacheng Sun, Xiaoyun Mi, Lijian Lei, Xiaoying Pan, Shuyi Chen, Zan Wang, Zhaohui Bai and Xiyan Zhang
CrystEngComm, 2015
DOI: 10.1039/C5CE01289A

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Highly selective and sensitive surface enhanced Raman spectroscopy (SERS) probes for the pesticide thiram have recently been reported by Zou and Wang et al.

SERS can provide low-cost, non-destructive, fast detection of potential environmental pollutants such as thiram.   This sulfur-containing pesticide and fungicide is commonly used to protect orchard fruits and soya but is toxic to humans both in acute doses and by long-term exposure to smaller quantities.

An effective SERS substrate has a rough metal surface – typically made of noble metals such as Ag – which adsorbs the molecules of interest.  The surface is coated on a glass or a core metal oxide particle, such as Fe₃O₄.   After oleate-modified Ag microspheres were found to possess selective thiram detection by surface-ligand exchange, attempts were made to generate Ag composite microspheres with oleate modifications, using a gel system.  However, the dumb-bell shaped particles produced showed a poor SERS performance, due to the lack of so-called hot-spots – areas where surface enhancement is intense.

In the new paper, the successful preparation of oleate-modified silver composite microspheres with dense hot-spots is demonstrated.  The Fe₃O₄ microspheres, capped with polyacrylate groups are prepared by a solvothermal method.  The carboxylate groups interact with Ag ions which are subsequently reduced using sodium borohydrate.  The surface Ag particles seed further coating by Ag in the presence of oleate in a gel system (see diagram below), completely covering the Fe₃O₄ microsphere in oleate-modified Ag nanoparticles.

The spherical particles produced show SERS detection of thiram at trace amounts, with the thiram spectrum detected at a concentration as low as 1 x 10⁻⁸ M.  Under the same conditions, two other common pesticides, methyl parathion and trichorfon, show no SERS signals. The results suggest that the system could potentially be used for the selective detection of traces of thiram in solution.

For more details, see the full paper at:

Gel-assisted synthesis of oleate-modified Fe₃O₄@Ag composite microspheres as magnetic SERS probe for thiram detection
Haihong Zheng, Bingfang Zou, Lin Chen, Yongqiang Wang, Xiaoli Zhang and Shaomin Zhou
CrystEngComm, 2015, Advance Article
DOI: 10.1039/C5CE01017A

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

A facile new preparation of shape-controlled tungsten trioxide (WO₃) sensors is reported in a recent paper by Zhang et al.  These sensors show good selectivity towards the hazardous gas hydrogen sulfide (H₂S) at a relatively low operating temperature.

Detection of hazardous gases is necessary to monitor environmental pollution and ensure levels do not exceed legally permitted limits.  In the case of H₂S, the general industry ceiling limit is 20 ppm.  At concentrations of above 50 ppm, eye damage is likely and at higher concentrations (above 320 ppm) pulmonary oedema and breathing problems resulting in death can occur.  There is, therefore, a demand for cheap, reliable and selective sensors for identifying low concentrations of H₂S.

Metal-oxide semiconductors such as WO₃ are attractive potential sensors which are relatively cheap and easy to fabricate.  As the sensing ability of the particles depends on their morphology, the preparation of shape-controlled particles is a requirement.  Zhang et al achieve this by reacting sodium tungstate and potassium sulfate in an acidic environment.  Adding oxalic acid and heating at 100^oC then calcining the resulting product produces WO₃ microflowers, of diameter 16 μm. Study of the reaction shows it can be divided into four processes.  Crucially, during the final stage, needle-like nanosheets grow radially from central particles to produce a flower-like morphology (see the scheme below).

These particles have excellent potential for application as H₂S sensors – at 160^oC they show high sensitivity and sensor response along with good repeatability and selectivity towards H₂S.  The high performance of WO₃ microflowers is related to their structure.  They are assembled from nanosheets composed of several nanowhiskers in parallel, giving highly exposed surfaces and so more pathways for gas absorption and electron exchange.  The nanosheets are homogeneous and single-crystalline so electron transport can occur between particles without overcoming boundary barriers which would decrease the sensitivity.

For more details, read the full paper at:

Low-temperature solvothermal synthesis of hierarchical flower-like WO₃nanostructures and their sensing properties for H₂S
Bingxin Xiao, Qi Zhao, Chuanhai Xiao, Tianye Yang, Pan Wang, Fei Wang, Xiaodong Chen and Mingzhe Zhang
CrystEngComm, 2015
DOI: 10.1039/C5CE00870K

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.