Energy transfer probe for the characterization of luminescent photonic crystals morphology

doi:10.1016/j.jlumin.2010.10.027

Journal of Luminescence

Volume 131, Issue 3, March 2011, Pages 449-452

https://doi.org/10.1016/j.jlumin.2010.10.027 Get rights and content

Abstract

We evaluated energy transfer probe for the characterization of luminescent photonic crystals morphology. It demonstrates a monomolecular filming of fluorescent chelated complexes inside photonic crystal voids. Either direct fluorescence quenching of excited fluorescent donors by the acceptors in case of low concentration of fluorescent centers or fluorescence quenching accelerated by energy migration over fluorescent donor ions in case of 100% of sites occupied by donors is demonstrated in 2D space contrarily to the powder samples of the same complexes where energy transfer occurs in 3D space.

Introduction

We evaluated energy transfer probe for the characterization of photonic crystals morphology. The method is based on the analysis of energy transfer kinetics from an excited fluorescent impurity centers (donors) to quenching acceptors randomly distributed in various restricted geometries [1]. Employing it, we determined a way of filling by a chromophore of the opal voids. There are two main options for a chromophore to fill the voids: first, chromophore forms a monomolecular film inside a void, and second, the room inside a void is more or less filled by chromophore. The first situation is described by the energy transfer kinetics in 2D space, while the second by that in 3D space. At the same time concentration of donor ions strongly influences on the energy transfer kinetics. In the case of low concentration of luminescent donors, it is usually a direct (static) energy transfer (DET) to acceptors [1], while in the case of high donor concentration, the energy migration over donor ions accelerates fluorescent quenching on the acceptors [2]. In the paper, we considered both the cases of energy transfer either with or without energy migration. We used chelated complexes of rare-earth (RE) ions as the chromophore. We used photonic crystal made of inverted opals in silica (SiO₂) with voids (D≈500 nm) filled by chromophore–coordination complexes of yttrium with 2-pyrazinecarboxylic acid co-doped by Tb³⁺. Reflection of (1 1 1) plain forms the stop band with a spectral maximum close to 890 nm which is far away from the chromophore green fluorescence. According to the crystal structure of [Tb(pyca)₃(H₂O)₂]·nH₂O its unit cell is 3-dimensional parallelepiped with a=19.589, b=12.055, and c=20.015 Å, which contains eight terbium ions [3]. At the same time the unit cell contains four Tb³⁺ ions in each of the three mutually orthogonal planes. In case of DET probe, low concentration of Tb³⁺ [Y_0.99Tb_0.01(pyca)₃(H₂O)₂]·nH₂O is employed. These complexes are liable to formation of hydrates of different structure and contain water molecules either bonded or unbonded to central ion. The Tb³⁺ ions appear as fluorescent donors and OH⁻-ions of unbounded water molecules appear as randomly distributed acceptors contrarily to the ordered acceptor system of CO, CN, and OH molecular groups coordinated to metal ions at fixed minimal distances R_min≈2.4–2.7 Å. The energy transfer to these groups is responsible for initial exponential ordered stage of energy transfer kinetics. We did not analyze this rather short stage because it cannot give appropriate information about a spatial dimension of the matter. The influence of donor–donor energy migration on fluorescence quenching of chromophore is analyzed in the [Tb(pyca)₃(H₂O)₂]·nH₂O sample with 100% concentration of the Tb³⁺ luminescent centers.

Section snippets

Experimental technique

Samples are prepared using the following procedure. First, monodisperse polystyrene microspheres are synthesized by emulsifier-free heterogeneous polymerization of styrene using potassium persulfate as initiator. Glass slides are thoroughly cleaned and immersed in ∼1 vol% aqueous suspension of microspheres. The temperature used for the film growth is 50 °C with a precision of ±1 °C. The samples are left undisturbed until the end of the films growth (∼24 h). Then the synthesized colloidal crystal

Results and discussions

The measured fluorescence kinetics of the inverted opaline sample filled by the Y_0.99Tb_0.01(pyca)₃(H₂O)₂]·nH₂O complexes exhibits long nonexponential millisecond decay within almost three orders of magnitude with fast nanosecond decay at the very beginning (Fig. 1, curve 1). The reason of fast decay is the contribution of unspecified portion of laser pulse (approximately one order of magnitude from initial value), which is in spite of all our precautions detected by PMT and added to

Conclusion

We demonstrated that the energy transfer probe can be a powerful tool for the characterization of luminescent photonic crystal morphology. It can be used to monitor the way of filling of photonic crystal voids by luminescent material when fluorescence is quenched by intrinsic acceptors. The method can be used either for low concentrations of fluorescent centers of rare-earth ions (donors) in its direct energy transfer (DET) mode or for high concentrations of fluorescent centers when energy

Acknowledgments

This work was partially supported by the Russian Academy of Sciences in frame of Program #27 (the Basics for the Fundamental Studies of Nanotechnologies and Nanomaterials) and by the Russian Foundation for Basic Research, projects #08-02-01058-a, #10-02-08109-3, #08-03-00938_a, and #09-03-12191.

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Journal of Luminescence

Abstract

Introduction

Section snippets

Experimental technique

Results and discussions

Conclusion

Acknowledgments

References (8)

J. Alloys Compd.

J. Chem. Phys.

Usp. Fiz. Nauk

Ann. Phys.

Ztschr. NaturForsch.

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