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Optics Express

Optics Express

  • Vol. 17, Iss. 7 — Mar. 30, 2009
  • pp: 5885–5890
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Optical gain at 1550 nm from colloidal solution of Er3+-Yb3+ codoped NaYF4 nanocubes

Xiaofeng Liu, Yingzhi Chi, Guoping Dong, E Wu, Yanbo Qiao, Heping Zeng, and Jianrong Qiu  »View Author Affiliations


Optics Express, Vol. 17, Issue 7, pp. 5885-5890 (2009)
http://dx.doi.org/10.1364/OE.17.005885


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Abstract

We demonstrated optical amplification at 1550 nm with a carbon tetrachloride solution of Er3+-Yb3+ codoped NaYF4 nanocubes synthesized with solvo-thermal route. Upon excitation with a 980 nm laser diode, the nanocube solution exhibited strong near-infrared emission by the 4I13/24I15/2 transition of Er3+ ions due to energy transfer from Yb3+ ions. We obtained the highest optical gain coefficient at 1550 nm of 0.58 cm-1 for the solution with the pumping power of 200 mW. This colloidal solution might be a promising candidate as a liquid medium for optical amplifier and laser at the optical communication wavelength.

© 2009 Optical Society of America

1. Introduction

2. Experimental

The NPs of Yb3+-Er3+ codoped NaYF4 (a host of low vibration energy) were synthesized by a solvo-thermal route [12

12. X. Wang, J. Zhuang, Q. Peng, and Y. Li, “A general strategy for nanocrystal synthesis,” Nature 437, 121–1242005. [CrossRef] [PubMed]

]. In a typical process, 10 ml aqueous solution (0.05 M) of rare earth nitrate was added to a mixture of 10 mL ethanol, 10 mL oleic acid (OA) and 0.6g NaOH. After mild stirring for 30 min, the milky solution was transferred to a Teflon-lined stainless steel autoclave (50 mL) and heated at 160°C for 5 h. After natural cooling to ambient temperature, the nanocrystals deposited at the bottom of the Teflon bottle was washed with ethanol and collected by centrifugation. The obtained nanocrystals can be readily redistributed in organic solvents like cyclohexane, benzene and carbon tetrachloride (CCl4). In the present work CCl4 was used as the solvent based on following three factors: (1) it does not exhibit absorption bands in NIR region because of its low fundamental vibration energy, (2) it eliminates any residual H2O that serves as an effective quencher for NIR emission, and (3) it has a relatively high refractive index compared with other non-polar solvents and therefore minimizes loss of light due to Rayleigh scattering. The phase composition and the morphology of the products were characterized by X-ray diffraction (XRD, Rigaku D/MAX-RA) and transmission electron microscopy (TEM, Hitachi Model H-600), respectively. A quartz vessel of 10×10×50 mm3 filled with the colloid solution of the NPs was used for the spectroscopic measurement and optical amplification experiment. The absorption and the emission spectra were measured with a Jasco V570 UV/VIS/NIR spectrophotometer, and a Zolix SBP 300 spectrofluorometer equipped with an InGaAs detector, respectively.

3. Results and discussion

Figure 1(a) shows the X-ray diffraction (XRD) pattern of the Yb3+-Er3+ codoped NaYF4 NPs. All the diffractions peaks can be well indexed to a cubic structure of Fm3m (PDF No. 39-0724). Figure 1(b) presents the TEM images of the nanocrystals. It is observed that all of the NPs crystallized into well-defined nanocubes with an average dimension of approximately 25 nm×25 nm, as shown in Fig. 1(c). With a more detailed observation we find that the NPs are covered with thin sheath of approximately 3 nm in thickness. This might be the OA layer formed in situ during solvo-thermal synthesis and attached to the surface of the nanocrystals, leaving its alkyl chains outside. As a result, the NPs are provided with hydrophobic surfaces and became soluble and stable in different organic solvents.

Fig. 1. Structural characteristics of the Yb3+-Er3+ codoped NaYF4 nanoparticles: (a) XRD pattern, (b) typical TEM image, insert is an image of a single nanocube covered by thin sheath of OA, and (c) size distribution of the nanoparticles obtained by counting the size of approximately 500 separate nanoparticles.

The nanocubes were dispersed in CCl4 to form a stable colloid solution with a concentration of 1.0wt%. This colloid is highly transparent as observed by naked eyes and remain stable without of noticeable precipitation of NPs for over 48 h. The concentration of 1.0wt% for NPs-colloid system was carefully determined considering the balance between the transparency and NIR emission intensity of the colloid. Figure 2 shows the transmission spectrum of the colloid solution in the wavelength region of 200 nm - 2000 nm. The absorption peak due to the Yb3+: 2 F 7/22 F 5/2 transition that located at around 980 nm can be clearly identified. In contrast, the f-f transition peaks of Er3+ can not be observed because of its low concentration and absorption section. Other weak peaks located at around 1400 nm, 1700 nm, and 1800 nm can be assigned to the double-frequency of the different vibration modes of alkyl chains [13

13. J. A. Dean, Lange’s Handbook of Chemistry, 15th Ed. (McGraw-Hill, 1999).

, 14

14. L. Wang and Y. Li, “Na(Y1.5Na0.5)F6 Single-Crystal Nanorods as Multicolor Luminescent Materials,” Nano Lett. 6, 1645–1649 (2006). [CrossRef] [PubMed]

] that cover the surfaces of the nanocubes as have been confirmed by TEM in Fig. 1(b).

Fig. 2. Transmission spectrum of the colloidal solution containing 1wt.% Yb3+-Er3+ codoped NaYF4, insert is the graph of a quartz vessel (10×10×50 mm3) filled with the nanocube solution.
Fig. 3. Emission spectra of the solution containing 1wt.% of NaY80%-x%Yb20%Erx%F4 (x=0.5, 1, 2, 5, 10) upon excitation by a 980 nm LD, insert shows the decay curves of colloids with Er3+ concentration in the nanocubes of x=2, and 10.

The dependence of the NIR emission intensity on the doping concentration of Er3+ due to its 4 I 13/2+4 I 15/2 transition was measured with the excitation at 980 nm, and the results are given in Fig. 3. For the Yb3+-Er3+ ions pair, the 980 nm pumping light is absorbed mainly by Yb3+ through the transition of 2 F 7/22 F 5/2 as it has a high absorption cross section at this wavelength compared with Er3+. Afterwards, energy transfer from Yb3+ to Er3+ occurs, resulting in the population of 4 I 11/2 of Er3+. The emission at 1550 nm then occurs after Er3+ relaxes nonradiatively to its 4 I 13/2 level. Here, for the Yb3+-Er3+ codoped NaYF4 (NaY80%-x%Yb20%Erx%F4), we fixed the Yb3+ concentration at 20%, and changed the Er3+ concentration (x%) from 0.5% to 10%. We obtained the highest emission intensity with Er3+ concentration of 2% with a full width at half maximum (FWHM) of 85 nm (approximately 360 cm-1 or 0.044 eV), and this colloid was used for the demonstration of optical amplification. A higher Er3+ concentration results in a decrease in emission intensity, and an increase in the decay rate of the NIR luminescence. This behavior can be understood by considering self-absorption of Er3+ ions, and enhanced possibility of cross relaxation between nearby Er3+ ions that leads to a high nonradiative rate under high Er3+ concentration. The average lifetimes estimated by (where I(t) stands for the intensity at time t [15

15. M. Y. William, S. Shionoya, and H. Yamamoto, Phosphor Handbook, 2nd ed., (CRC press, 2006), chap. 14.

]) are 1.22 ms and 0.41 ms for colloidal solutions of nanocubes with the Er3+ concentration corresponding to x=2 and x=10, respectively. These lifetimes are close to that of the Er3+ doped LaF3 nanocrystals reported by Veggel et al. [7

7. J. W. Stouwdam and Frank C. J. M. van Veggel, “Near-infrared emission of redispersible Er3+, Nd3+, and Ho3+ doped LaF3 nanoparticles,” Nano Lett. 2, 733–737 (2002). [CrossRef]

]. Additionally, the decays curves shown in Fig. 3 deviate notably from single exponential decay function, suggesting that the radiative transition is accompanied by rapid nonradiative process probably due to strong coupling between the nanocubes and the different vibration modes of the solvent and the organic adsorbents.

Fig. 4. Optical amplification with the nanocube solution: (a) experimental setup for the measurement of optical gain: (1) 980 nm LD as the pumping beam, (2) 980 nm LD as the signal beam, (3) chopper, 200 Hz, (4) sample, quartz vessel filled with the nanocube solution, (5) filter, (6) InGaAs detector, and (7) digital oscilloscope, M1 and M2 are mirrors, and L1, L2 and L3 are lens; (b) comparison of the intensity for the amplified and the signal beam; (c) plot of gain coefficient as a function pumping power at 980 nm, and (d) plot of gain coefficient as a function of signal power.

4. Conclusion

In conclusion we have realized successfully optical amplification at 1550 nm from a colloidal solution containing Er3+-Yb3+ codoped NaYF4 nanocubes synthesized by a solvo-thermal route. We observed the highest optical gain coefficient at 1550 nm of 0.58 cm-1 with the colloidal amplifier at the pumping power of 200 mW at 980 nm. The results implies that RE-doped nanocrystal solution represents a new family of liquid laser medium that is advantageous over dye solutions as well as colloidal quantum dots due to its high photo-stability as well as low toxicity.

Acknowledgments

This work was financially supported by National Natural Science Foundation of China (Grant No. 50672087, No. 60707019 and No. 60778039), National Basic Research Program of China (2006CB806000) and National High Technology Program of China (2006AA03Z304).

References and links

1.

V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H. J. Eisler, and M. G. Bawendi, “Optical gain and stimulated emission in nanocrystal quantum dots,” Science 290, 314–317 (2000). [CrossRef] [PubMed]

2.

V. I. Klimov, S. A. Ivanov, J. Nanda, M. Achermann, I. Bezel, J. A. McGuire, and A. Piryatinski, “Single-exciton optical gain in semiconductor nanocrystals,” Nature 447, 441–446 (2007). [CrossRef] [PubMed]

3.

Q. Darugar, W. Qian, and M. A. El-Sayed, “Observation of optical gain in solutions of CdS quantum dots at room temperature in the blue region,” Appl. Phys. Lett. 88, 261108/1–261108/3 (2006). [CrossRef]

4.

R. Hardman, “A toxicologic review of quantum dots: Toxicity depends on physicochemical and environmental factors,” Environ. Health Persp. 114, 165–172 (2006). [CrossRef]

5.

H. Bao, Y. Gong, Z. Li, and M. Gao, “Enhancement effect of illumination on the photoluminescence of water-soluble CdTe nanocrystals: Toward highly fluorescent CdTe/CdS core-shell structure,” Chem. Mater. 16, 3853–3859 (2004). [CrossRef]

6.

G. M. Haugen, “Photodegradation of CdxZn1-xSe quantum-wells,” Appl. Phys. Lett. 66, 358–3601995. [CrossRef]

7.

J. W. Stouwdam and Frank C. J. M. van Veggel, “Near-infrared emission of redispersible Er3+, Nd3+, and Ho3+ doped LaF3 nanoparticles,” Nano Lett. 2, 733–737 (2002). [CrossRef]

8.

J. Wang, J. Hu, D. Tang, X. Liu, and Z. Zhen, “Oleic acid (OA)-modified LaF3: Er,Yb nanocrystals and their polymer hybrid materials for potential optical-amplification applications,” J. Mater. Chem. 17, 1597–1601 (2001). [CrossRef]

9.

R. Yu, K. Yu, W. Wei, X. Xu, X. Qiu, S. Liu, W. Huang, G. Tang, H. Ford, and B. Peng, “Nd2O3 nanoparticles modified with a silane coupling agent as a liquid laser medium,” Adv. Mater. 19, 838–842 (2007). [CrossRef]

10.

D. Zhang, C. Chen, C. Chen, C. Ma, D. Zhang, S. Bo, and Z. Zhen, “Optical gain at 1535 nm in LaF3:Er,Yb nanoparticle-doped organic-inorganic hybrid material waveguide,” Appl. Phys. Lett. 91, 161109/1–161109/3 (2007).

11.

R. Dekker, D. J. W. Klunder, A. Borreman, M. B. J. Diemeer, K. Wörhoff, A. Driessen, J. W. Stouwdam, and F. C. J. M. van Veggel, “Stimulated emission and optical gain in LaF3:Nd nanoparticle-doped polymer-based waveguides,” Appl. Phys. Lett. 85, 6104–6106 (2004). [CrossRef]

12.

X. Wang, J. Zhuang, Q. Peng, and Y. Li, “A general strategy for nanocrystal synthesis,” Nature 437, 121–1242005. [CrossRef] [PubMed]

13.

J. A. Dean, Lange’s Handbook of Chemistry, 15th Ed. (McGraw-Hill, 1999).

14.

L. Wang and Y. Li, “Na(Y1.5Na0.5)F6 Single-Crystal Nanorods as Multicolor Luminescent Materials,” Nano Lett. 6, 1645–1649 (2006). [CrossRef] [PubMed]

15.

M. Y. William, S. Shionoya, and H. Yamamoto, Phosphor Handbook, 2nd ed., (CRC press, 2006), chap. 14.

16.

B. Jaskorzynska, E. V. Vanin, S. He lmfrid, and A. Asseh “Gain saturation and pump depletion in high-efficiency distributed-feedback rare-earth-doped lasers,” Opt. Lett. 21, 1366–1368 (1996). [CrossRef] [PubMed]

OCIS Codes
(140.4480) Lasers and laser optics : Optical amplifiers
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence
(160.4236) Materials : Nanomaterials

ToC Category:
Materials

History
Original Manuscript: February 17, 2009
Revised Manuscript: March 20, 2009
Manuscript Accepted: March 23, 2009
Published: March 26, 2009

Citation
Xiaofeng Liu, Yingzhi Chi, Guoping Dong, E. Wu, Yanbo Qiao, Heping Zeng, and Jianrong Qiu, "Optical gain at 1550 nm from colloidal solution of Er3+-Yb3+ codoped NaYF4 nanocubes," Opt. Express 17, 5885-5890 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-7-5885


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References

  1. V. I. Klimov, A. A. Mikhailovsky, S. Xu, A. Malko, J. A. Hollingsworth, C. A. Leatherdale, H. J. Eisler, and M. G. Bawendi, "Optical gain and stimulated emission in nanocrystal quantum dots," Science 290, 314-317 (2000). [CrossRef] [PubMed]
  2. V. I. Klimov, S. A. Ivanov, J. Nanda, M. Achermann, I. Bezel, J. A. McGuire, and A. Piryatinski, "Single-exciton optical gain in semiconductor nanocrystals," Nature 447, 441-446 (2007). [CrossRef] [PubMed]
  3. Q. Darugar, W. Qian, and M. A. El-Sayed, "Observation of optical gain in solutions of CdS quantum dots at room temperature in the blue region," Appl. Phys. Lett.  88, 261108/1-261108/3 (2006). [CrossRef]
  4. R. Hardman, "A toxicologic review of quantum dots: Toxicity depends on physicochemical and environmental factors," Environ. Health Persp. 114, 165-172 (2006). [CrossRef]
  5. H. Bao, Y. Gong, Z. Li, and M. Gao, "Enhancement effect of illumination on the photoluminescence of water-soluble CdTe nanocrystals: Toward highly fluorescent CdTe/CdS core-shell structure," Chem. Mater. 16, 3853-3859 (2004). [CrossRef]
  6. G. M. Haugen, "Photodegradation of CdxZn1-xSe quantum-wells," Appl. Phys. Lett. 66, 358-3601995. [CrossRef]
  7. J. W. Stouwdam, and FrankC. J. M. van Veggel, "Near-infrared emission of redispersible Er3+, Nd3+, and Ho3+ doped LaF3 nanoparticles," Nano Lett. 2, 733-737 (2002). [CrossRef]
  8. J. Wang, J. Hu, D. Tang, X. Liu, and Z. Zhen, "Oleic acid (OA)-modified LaF3: Er,Yb nanocrystals and their polymer hybrid materials for potential optical-amplification applications," J. Mater. Chem. 17, 1597-1601 (2001). [CrossRef]
  9. R. Yu, K. Yu, W. Wei, X. Xu, X. Qiu, S. Liu, W. Huang, G. Tang, H. Ford, and B. Peng, "Nd2O3 nanoparticles modified with a silane coupling agent as a liquid laser medium," Adv. Mater. 19, 838-842 (2007). [CrossRef]
  10. D. Zhang, C. Chen, C. Chen, C. Ma, D. Zhang, S. Bo, and Z. Zhen, "Optical gain at 1535 nm in LaF3:Er,Yb nanoparticle-doped organic-inorganic hybrid material waveguide," Appl. Phys. Lett.  91, 161109/1-161109/3 (2007).
  11. R. Dekker, D. J. W. Klunder, A. Borreman, M. B. J. Diemeer, K. Wörhoff, A. Driessen, J. W. Stouwdam, and F. C. J. M. van Veggel, "Stimulated emission and optical gain in LaF3:Nd nanoparticle-doped polymer-based waveguides," Appl. Phys. Lett. 85, 6104-6106 (2004). [CrossRef]
  12. X. Wang, J. Zhuang, Q. Peng, and Y. Li, "A general strategy for nanocrystal synthesis," Nature 437, 121-1242005. [CrossRef] [PubMed]
  13. J. A. Dean, Lange's Handbook of Chemistry, 15th Ed. (McGraw-Hill, 1999).
  14. L. Wang and Y. Li, "Na(Y1.5Na0.5)F6 Single-Crystal Nanorods as Multicolor Luminescent Materials," Nano Lett. 6, 1645-1649 (2006). [CrossRef] [PubMed]
  15. M. Y. William, S. Shionoya, and H. Yamamoto, Phosphor Handbook, 2nd ed., (CRC press, 2006), Chap. 14.
  16. B. Jaskorzynska, E. V. Vanin, S. He lmfrid, and A. Asseh, "Gain saturation and pump depletion in high-efficiency distributed-feedback rare-earth-doped lasers," Opt. Lett. 21, 1366-1368 (1996). [CrossRef] [PubMed]

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