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.