Elsevier

Thin Solid Films

Volume 516, Issue 9, 3 March 2008, Pages 2376-2381
Thin Solid Films

Improvement of lasing properties of europium (III) complexes by increase of emission quantum yield

https://doi.org/10.1016/j.tsf.2007.04.092Get rights and content

Abstract

Deuterated Eu(III) complexes of tris-(hexafluoroacetylacetonato)europium(III) dehydrates (Eu(hfa-H)3(H2O)2), tris-(hexafluoroacetylacetonato)europium(III) bis(triphenylphospine oxide) (Eu(hfa-H)3(TPPO)2), tris(hexafluoroacetylacetonato) europium(III) 1,1′-biphenyl-2,2′-diylbis (diphenylphosphine oxide) (Eu(hfa-H)3(BIPHEPO)) were prepared by the exchange reaction via keto-enol tautomerism of the Eu(III) complexes with CD3OD. The emission quantum yields of the deuterated Eu(III) complexes were higher than those of corresponding non-deuterated Eu(III) complexes. The lasing properties of Eu(III) complexes in polymer thin film were measured by photo-pumping of Nd: YAG laser (355 nm). Percentages of ASE components in whole emission were increased by deuteration of the Eu(III) complexes.

Introduction

An organic medium incorporating lanthanide(III) complexes is expected to achieve compact laser and functional devices such as the polymer fiber laser, the liquid laser, and the plastic thin film laser [1]. Amplified emission of lanthanide(III) complexes using their ideal 4 level f–f transition has allowed the development of high-power laser materials [2]. In order to observe the amplified emission of lanthanide(III) complexes, dielectric sphere systems [3], [4] and polymer optical fiber systems [5], [6] incorporating lanthanide(III) complexes have been reported. We also reported amplified spontaneous emission (ASE) of Eu(III) complex with low threshold energy by using of the polymer thin film system [7]. The emission quantum yield and ASE properties are directly linked to the vibrational structures of luminescent lanthanide(III). In earlier studies, we reported the suppression of radiationless quenching in fluid Nd(III) systems by coordinating Nd(III) with β-diketonato ligands composed only of low-vibrational C–D and C–F bonds. Suppression of such vibrational relaxation in lanthanide(III) complexes requires deuteration of C–H and O–H bonds or replacement of C–H bonds with C–F bonds in ligating molecules [8]. The low-vibrational lanthanide(III) complexes without C–H and O–H bonds would lead to increase of the emission quantum yields and enhancement of ASE properties.

In this study, we report on enhancement of ASE properties by using polymer thin films incorporating deuterated Eu(III) complexes without C–H or O–H bonds for the first time. The deuterated Eu(III) complexes tris-(hexafluoroacetylacetonato)europium(III) dehydrates (Eu(hfa-D)3(D2O)2: 2), deuterated tris-(hexafluoroacetylacetonato)europium(III) bis(triphenylphospine oxide) (Eu(hfa-D)3(TPPO)2: 4), deuterated tris(hexafluoroacetylacetonato) europium(III) 1,1′-biphenyl-2,2′-diylbis (diphenylphosphine oxide) (Eu(hfa-D)3(BIPHEPO): 6) (Fig. 1) were prepared by the exchange reaction via keto-enol tautomerism of the Eu(III) complexes with CD3OD. The emission quantum yields of deuterated Eu(III) complexes (2: 0.31, 4: 0.90 and 6: 0.87) were higher than those of corresponding non-deuterated Eu(III) complexes (1: 0.11, 3: 0.65 and 5: 0.60) in acetone-d6. We observed that amplification magnitudes of ASE from polymers thin film containing deuterated Eu(III) complexes were larger than those from polymer thin films containing non-deuterated Eu(III) complexes [7].

Section snippets

Apparatus

Infrared spectra used to identify the synthesized materials were obtained with a Perkin-Elmer FT-IR 2000 spectrometer. Elemental analyses were performed with a Perkin-Elmer 240C. 13C and 19F NMR data were obtained with a JEOL EX-270 spectrometer. 13C NMR chemical shifts were determined using tetramethylsilane (TMS) as an internal standard, while 19F NMR chemical shifts were determined using hexafluorobenzene as an external standard (δ =  162.0 (s, Ar–F) ppm).

Materials

Europium acetate monohydrate (99.9%),

Photophysical properties of Eu(III) complexes

Samples for measurements of the luminescence of Eu(III) complexes in organic media were prepared under deoxygenated conditions. Table 1 shows the photophysical properties of the Eu(III) complexes in acetone-d6. The FWHM (5D07F2) of Eu(III) complexes with BIPHEPO (5 and 6) were smaller than those of Eu(III) complexes with coordination water (1 and 2) and TPPO ligands (3 and 4). The FWHM is directly linked to the characteristics of perturbation of f-orbitals of Eu(III) affected by the

Conclusions

To increase emission quantum yields of Eu(III) complexes, deuteration of C–H and O–H bonds were carried. Low-vibrational ligands by deuteration lead to enhancement of the emission quantum yields, the Einstein coefficients A and stimulated emission cross-sections. As the results of ASE measurements, the enhancement of ASE properties based on low-vibrational structures of deuterated Eu(III) complexes were demonstrated for the first time. The improvement of ASE properties might be due to enhanced

Acknowledgements

This work was supported by a Grant-in-Aid for Scientific Research (No. 12450345) and a Grant-in-Aid for Scientific Research on Priority Areas (417) (No. 15033245) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of the Japanese Government and Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists and by a Grant-in-Aid for Scientific Research on Priority Area A of “Panoscopic Assembling and High Ordered Functions for Rare Earth

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