Received: November 2024

DOI 10.17677/fn20714807.2024.06.04

Fluorine Notes, 2024, 157, 7-8

Fluoride nanocrystals NaYF₄:Yb³⁺,Er³⁺ for polymer waveguide amplifiers of telecommunication C-range

K.V. Khaidukov, P.A. Demina, I.O. Goryachuk, V.I. Sokolov

National Research Centre "Kurchatov Institute", Moscow, Russia

Annotation: Fluoride nanocrystals β-NaYF₄:Yb³⁺,Er³⁺ in the size range of 40-50 nm, possessing intense photoluminescence in the telecommunication C - wavelength range λ= 1550 ± 30 nm when pumped by IR radiation with λ= 980 nm, have been synthesized. The method of introduction of nanocrystals into polymer matrix in high concentration was developed. Using the obtained composite material, waveguide amplifiers of optical radiation for the C - range of the spectrum were fabricated. The obtained amplification at the wavelength λ= 1532 nm was 19 dB at the waveguide length of 15 mm.

Keywords: fluoride nanocrystals, rare-earth elements, photoluminescence, waveguide optical amplifiers.

Introduction

Fluoride nanocrystals (NaYF₄, NaLuF₄, etc.) doped with ytterbium and erbium ions are promising for the creation of compact waveguide amplifiers operating in the telecommunication C-band of the spectrum near 1550 nm. For this purpose, nanocrystals are introduced into a polymer matrix in high concentration and the resulting composite material is used to form single-mode optical waveguides [1-6]. Waveguide amplifiers can be used, for example, in high-speed optical data buses for microprocessor-based computing devices on printed circuit boards [7]. By the method of thermal decomposition of trifluoroacetates of rare-earth elements and sodium in a mixture of oleic acid and 1-octadecene, we synthesized nanocrystals β-NaYF₄:Yb³⁺,Er³⁺ in the size range of 40-50 nm with an inert silicon oxide shell. The nanoparticles were incorporated into SU-8 photoresist at a concentration of 40%, which was used to form the waveguides. When pumping with 980 nm IR radiation, the amplification at the wavelength λ= 1532 nm in a 15 mm long waveguide was 19 dB.

Experimental part

Commercial reagents: yttrium, ytterbium, erbium oxides, sodium carbonate, oleic acid 90%, 1-octadecene 90% (Sigma-Aldrich) and trifluoroacetic acid 99% (PanReac) were used for the synthesis of fluoride nanocrystals β-NaYF₄:Yb³⁺,Er³⁺. The nanocrystals were synthesized according to the methodology we described in [7]. The Er³⁺ concentration in the β-NaYF₄ matrix was 2%. Figure 1a shows a photograph of the synthesized nanoparticles obtained using TEM electron microscope and Figure 1b shows their photoluminescence (PL) spectrum in down-conversion excited by 980 nm IR radiation. The intense PL band with a center near 1532 nm and 74 nm wide is due to ⁴I_13/2→ ⁴I_15/2 transitions in Er³⁺ ions. Structural diagnostics of the obtained nanocrystals, carried out on a Rigaku Miniflex600 X-ray diffractometer (Cu, λ= 1.54184 Å), showed that they have hexagonal β-phase crystal lattice.

Figure 1. (a) TEM photograph of synthesized fluoride nanocrystals β-NaYF₄:Yb³⁺,Er³⁺.
(b) PL spectrum of the nanocrystals when pumping by 980 nm IR radiation. The simplified energy level system of ytterbium and erbium is shown in the inset.

The synthesized nanoparticles β-NaYF₄:Yb³⁺,Er³⁺ were introduced into the photoresistive material SU-8 at a concentration of 40%. The obtained composite material was used to form single-mode optical waveguides on a silicon substrate with a thermally grown oxide layer by UV photolithography (wavelength 365 nm). The width and thickness of the waveguide were 6 × 6 μm. Figure 2 shows the measured dependence of the gain coefficient of the optical signal at a wavelength of 1532 nm in a 15 mm long waveguide on the pumping radiation power with λ= 980 nm. As follows from Figure 2, the achieved gain coefficient is 19 dB.

Figure 2. The dependence of the gain coefficient (Gain) of the optical signal at a wavelength of 1532 nm in a waveguide amplifier with a 15 mm length from the pumping radiation power P_pump at a wavelength of 980 nm.

Conclusion

The possibility of creating compact waveguide amplifiers for a telecommunication C-range of wavelengths near 1550 nm based on fluoride nanocrystals of β-NaYF₄:Yb³⁺,Er³⁺ with a shell of silicon oxide introduced into the photoresist SU -8 has been demonstrated. The obtained gain at a wavelength of 1532 nm in a 15 mm long waveguide was 19 dB. The synthesized NaYF₄:Yb³⁺,Er³⁺ nanocrystals are also promising for the creation of waveguide lasers with distributed feedback.

Acknowledgments

The work was carried out within the state assignment of NRC "Kurchatov Institute"

References

1. Y. Fu, T. Sun, J. Li, Y. Tang, Y. Yang, S. Tao, F. Wang, D. Zhang, G. Qin, Z. Jia, D. Zhao, W. Qin, (S+C)-band polymer waveguide amplifier based on Tm³⁺ and Er³⁺ layer-doped core-shell nanoparticles, Optics Letters, 2023, 48(2), 391.
2. X. Liu, M. Zhang, G. Hu, Gain Enhancement of the Optical Waveguide Amplifier Based on NaYF₄/NaLuF₄: Yb, Er NPs-PMMA Integrated with a Si₃N₄ Slot, Nanomaterials, 2022, 12, 2937.
3. T. Sun, Y. Fu, X. Zhang, J. Yan, F. Wang, D. Zhang, Gain enhancement of polymer waveguide amplifier based on NaYF₄: Er³⁺, Yb³⁺ nanocrystals using backward pump scheme, Optics Communications, 2021, 488, 126723.
4. H. Gao, H. Li, G.F.R. Chen, P. Xing, M.C. Tan, D.T.H. Tan, 3D printed and spiral lithographically patterned erbium‑doped polymer micro-waveguide amplifiers, Scientific Reports, 2021, 11, 21292.
5. Z. Zhou, J. Xue, B. Zhang, C. Wang, X. Yang, W. Fan, L. Ying, Z. Zheng, Y. Xie, Y. Wu, X. Yang, D. Zhang, Optical gain based on NaYF₄: Er, Yb nanoparticles-doped polymer waveguide under convenient LED pumping, Appl. Phys. Lett, 2021, 118, 173301.
6. Y. Yang, F. Wang, S. Ma, M. Zhou, Y. Lang, G. Qin, D. Zhang, W. Qin, D. Zhao, X. Zhang, Great enhancement of relative gain in polymer waveguide amplifier using NaYF₄/NaLuF₄:Yb,Er‑PMMA nanocomposite as gain media, Polymer, 2020, 188, 122104.
7. V. I. Sokolov, I. M. Asharchuk, I.O. Goryachuk, S.I. Molchanova. Synthesis of fluoride NaYF4/Yb/Tm, NaYF4/Yb/Er micro- and nanocrystals and their characterization by UV optical microscopy method, Fluorine Notes, 2021, 6(139), 7-8.

ARTICLE INFO
Received 29 November 2024
Accepted 17 December 2024
Available online December 2024

Recommended for publication by PhD O.V. Bryzgalova

eLIBRARY Document Number (EDN) XOONAM

Fluorine Notes, 2024, 157, 7-8