Laser action in Tb ( OH ) 3 / SiO 2 photonic crystals

Photonic crystals of Tb(OH)3/SiO2 core/shell nanospheres with different periodicities were used as a resonant cavity to explore laser action. By changing the particle size, the optical stop band of the photonic crystals can be tuned to coincide with the multiple emission bands of terbium ions. An overlap of the stop band on the multiple emissions of the active materials embedded inside the photonic crystals offered a good chance for resonance. Lasing emissions arising from terbium ions occurred near the band edge of the PCs were demonstrated. ©2008 Optical Society of America OCIS codes:(050.5298) Photonic crystals; (140.3380) Laser materials; (260.5740) Resonance. References and links 1. E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and electronics,” Phys. Rev. Lett. 58, 2059-2062 (1987). 2. S. John, “Strong localization of photons in certain disordered dielectric superlattices,” Phys. Rev. Lett. 58, 2486-2489 (1987). 3. N. Tétreault, A. C. Arsenault, A. Mihi, S. Wong, V. Kitaev, I. Manners, H. Miguez, and G. A. Ozin, “Building tunable planar defects into photonic crystals using polyelectrolyte multilayers,” Adv. Mater. 17, 1912-1916 (2005). 4. E. Feltin, G. Christmann, R. Butté, J.-F. Carlin, M. Mosca, and N. Grandjean, “Room temperature polariton luminescence from a GaN/AlGaN quantum well microcavity,” Appl. Phys. Lett. 89, 071107071109 (2006). 5. R. K. Price, “Widely tunable 850-nm metal-filled asymmetric cladding distributed Bragg reflector lasers,” IEEE J. Quan. Elec. 42, 667-674 (2006). 6. M. Skorobogatiy and A. V. Kabashin, “Photon crystal waveguide-based surface plasmon resonance biosensor,” Appl. Phys. Lett. 89, 143518-143520 (2006). 7. J. S. Xia, Y. Ikegami, Y. Shiraki, N. Usami, and Y. Nakata, “Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature,” Appl. Phys. Lett. 89, 201102-201104 (2006). 8. A. C. Arsenault, T. J. Clark, G. V. Freymann, L. Cademartiri, R. Sapienza, J. Bertolotti, E. Vekris, S. Wong, V. Kitaev, I. Manners, R. Z. Wang, S. John, D. Wiersma, and G. A. Ozin, “From colour fingerprinting to the control of photoluminescence in elastic photonic crystals,” Nat. Mater. 5, 175 -179 (2006). 9. Y. Zhang, C. Shi, C. Gu, L. Seballos, and J. Z, Zhang, “Liquid core photonic crystal fiber sensor based on surface enhanced Raman scattering,” Appl. Phys. Lett. 90, 193504-193506 (2007). 10. S. Woong, B. Park, and Y. P. Lee, “Polarized laser emission from an anisotropic one-dimensional photonic crystal laser,” Appl. Phys. Lett. 90, 161108-161110 (2007). 11. O. Painter, R. K. Lee, A. Scherer, A. Yariv, J. D. O’Brien, P. D. Dapkus, and I. Kim, “Two dimensional photonic band gap defect mode laser,” Science 284, 1819-1821 (1999). 12. F. Jin, C. F. Li, X. Z. Dong, W. Q. Chen, and X. M. Duan, “Laser emission from dye-doped polymer film in opal photonic crystal cavity,” Appl. Phys. Lett. 89, 241101-241103 (2006). 13. W. Cao, A. Muñoz, P. P. Muhoray, and B. Taheri, “Lasing in a three-dimensional photonic crystal of the liquid crystal blue phase II,” Nature Mater. 1, 111-113 (2002). 14. A. D. Ford, S. M. Morris, and H. J. Coles, “Photonics and lasing in liquid crystals,” Materialstoday 9, 3642 (2006). 15. S. Chakravarty, P. Bhattacharya, S. Chakrabarti, and Z. Mi, “Multiwavelength ultralow-threshold lasing in quantum dot photonic crystal microcavities,” Opt. Lett. 32, 1296-1298 (2007). 16. G. R. Maskaly, M. A. Petruska, J. Nanda, I. V. Bezel, R. D. Schaller, H. Htoon, J. M. Pietryga, and V. I. Klimov, “Amplified spontaneous emission in semiconductor-nanocrystal/synthetic-opal composites: optical-gain enhancement via a photonic crystal pseudogap,” Adv. Mater. 18, 343-347 (2006). #98662 $15.00 USD Received 14 Jul 2008; revised 15 Sep 2008; accepted 17 Sep 2008; published 6 Oct 2008 (C) 2008 OSA 13 October 2008 / Vol. 16, No. 21 / OPTICS EXPRESS 16697 17. M. Scharrer, A. Yamilov, X. Wu, H. Cao, and R. P. H. Chang, “Ultraviolet lasing in high-order bands of three-dimensional ZnO photonic crystals,” Appl. Phys. Lett. 88, 201103-201105 (2006). 18. X. Jiang, Q. Yang, G. Vienne, Y. Li, L. Tong, J. Zhang, and L. Hu, “Demonstration of microfiber knot laser,” Appl. Phys. Lett. 89, 143513-143514 (2006). 19. H. Amekura, A. Eckau, R. Carius, and Ch. Buchal, “Room-temperature photoluminescence from Tb ions implanted in SiO2 on Si,” J. Appl. Phys. 84, 3867-3871 (1998). 20. Y. S. Lin, Y. Hung, H. Y. Lin, Y. H. Tseng, Y. F. Chen, and C. Y. Mou, “Photonic crystals from monodisperse lanthanide-hydroxide-at-silica core/shell colloidal spheres,” Adv. Mater. 19, 577-580 (2007). 21. J. Huang, N. Eradat, M. E. Raikh, Z. V. Vardeny, A. A. Zakihidov, and R. H. Baughman, “Anomalous coherent backscattering of light from opal photonic crystals,” Phys. Rev. Lett. 86, 4815-4818 (2001). 22. J. F. Galisteo-López and C. López, “High-energy optical response of artificial opals,” Phys. Rev. B 70, 035108-0351014 (2004). 23. R. Reisfeld and C. K. Jørgensen, Lasers and excited states of Rare Earths (Springer, Berlin, 1977). 24. H. Aizawa, T. Katsumata, S. Komuro, T. Morikawa, H. Ishizawa, and E. Toba, “Fluorescence thermometer based on the photoluminescence intensity ratio in Tb doped phosphor materials,” Sens. Actu. A. 126, 78-82 (2006). 25. K. Kiyota, T. Kise, N. Yokouchi, T. Ide, and T. Baba, “Various low group velocity effects in photonic crystal line defect waveguides an their demonstration by laser oscillation,” Appl. Phys. Lett. 88, 201904201906 (2006).


Introduction
Since dimensional photonic crystals (PCs) developed for years, many efforts have been concentrated on their optical properties, especially the photonic band gap [1][2][3].Mainly due to Bragg diffraction, periodical structures in submicron range lead to photon localization in the forbidden region.Recently, various applications of PCs have been carried out as a reflector [4,5], a sensor [6], or to enhance luminescence [7,8] and Raman spectroscopy [9].In addition, PCs were often used to induce lasing emission that luminescent materials embedded inside PCs can be excited to interact with them, as well as pumping in a resonance cavity [10,11].So far, low threshold lasing has been demonstrated with the combination of opal/inverse opal PCs and several active materials.Examples are fluorescent dye molecules or semiconductors embedded in 1-D, 2-D, and 3-D PCs, in which the photonic stop band can range from ultraviolet (UV) to near infrared (NIR) [12][13][14][15][16].
Despite lasing emissions have been developed with various materials in PCs, some obstacles still need to be overcome.In general, dye is accompanied with a broader band emission than the width of the photonic stop band [12], resulting in incomplete photon suppression inside PCs.Moreover, luminescence of dye is easily quenched especially under high power excitation.Meanwhile, for a large area of semiconductor PCs, the developed opal or inverse structures have the disadvantage of generating defect-free emission during the fabrication process [17].To achieve high lasing efficiency and complete photon suppression, strong and stable luminescent active materials embedded in PCs are necessary.Recently, Er 3+ doped-fiber has been used as a resonance cavity to perform lasing modes [18].With strong, stable, and narrow multiple emissions of intra-4f transition in near infrared range, it offers a very practical opportunity for the application in optical communication.Similarly, Tb 3+ , one kind of rare earth ions with emission bands from UV to visible range, also has the same advantages [19].In one of our published reports, Tb ions encapsulated in monodispersed silica nanoparticles (Tb(OH) 3 /SiO 2 core/shell nanosphere) have been successfully synthesized [20].After self-assembling in a closed pack structure, the periodicity of these nanospheres exhibits a pronounced photonic stop band.In addition to preventing coalescence and controlling size, the SiO 2 shell is very useful in manipulating interparticle interaction and in biological targeting research.By taking the advantages of the well-defined PCs developed in our previous work [20], here we demonstrate laser action of 5 D 3 → 7 F 6 transition of Tb ions based on the assistance of the formation of optical stop band in PCs.Our results provide an excellent alternative for creating reliable solid state emitters, laser materials, as well as biological markers.

Experiment
Tb(OH) 3 /SiO 2 core/shell nanospheres were synthesized by a one-pot method and deposited on a quartz or silicon (100) substrate by a slow evaporation method.Details were described in our previous report [20].The particle size of the nanospheres ranged from 125 nm to 300 nm was examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM, JEOL JSM-6500).After the nanospheres were assembled to several cm 2 in area as PCs, the samples were excited at room temperature by a Q-switched Nd: YAG laser (266 nm, 3-5 ns pulse).The diameter of the laser beam focused on the sample is about 0.5 mm.200 nm as shown in Fig. 2(a).To confirm the fact that the peak at 490 nm really arises from the formation stop band due to the inherent nature of photonic crystals, we have performed the band structure calculation based on PWE (plane wave expansion) method as shown in Fig. 2(b).The experiment result is indeed consistent with the band structure calculation.By varying the nanospheres size, we can shift the stop band position from 330 nm to 650 nm, as shown in Fig. 2(b).The variation of the stop band versus particle size shows a linear relationship as predicted by the theory of Bragg diffraction [21].The slightly nonlinear behavior may be due to the variation of refractive index of silica in UV range, disorder, and the resulting changed filling fraction [22].Moreover, when the diameter of the nanospheres decreases and is comparable to that of the core material (10 nm), influence of Tb ions on effective refractive index needs to be considered.For single or random dispersed Tb(OH) 3 /SiO 2 core/shell nanoparticles, the luminescence spectrum reveals multiple emissions from 380 nm to 625 nm [23] as shown in Fig. 3(a).Among these emissions, most strong emission occurs at the transition from 5 D 4 to 7 F 5 bands.As the nanospheres were assembled showing a periodic nanostructure, relative emission intensities of 5 D 3 to 7 F 6, 5 D 3 to 7 F 5 , and 5 D 3 to 7 F 4 transitions with respect to other transitions change due to the inhibited propagating wave in photonic crystals.As shown in Fig. 3 (b), the emission bands of 497 nm were largely suppressed when the nanospheres with a diameter of 230 nm were assembled as photonic crystals.This behavior can be easily understood due to the formation of the stop band from 400 nm to 600 nm as shown in Fig. 2(a), and therefore the emission is confined inside the PCs and unable to escape away.

Results and discussions
To show lasing or optical resonance effect in PCs, the samples with a diameter of 230 nm (with stop band at around 500 nm) was chosen to demonstrate the influence on the excited luminescence spectrum.Figure 4(a) shows the emission spectra of Tb(OH) 3 /SiO 2 PCs with a diameter of 230 nm with different excitation energies.Below 74 μJ/pulse, the emission spectra at around 400 nm showed a broader emission peak.A sharp peak appears as the pumping energy is increased.The plot of emission intensity versus excitation current is shown in Fig. 4(b).After the pumping energy reached 74 μJ/pulse, the emission near 400 nm occurred as a protrusion, which is near the stop band edge.The narrow width of the emission and the threshold nature clearly prove the lasing emission behavior.Most emission in the stop band was suppressed due to the low photonic density of state (DOS).In contrast, high photonic density of states near the band edge can enhance the emission rate.Laser emission can be achieved with the relative low group velocity and high photonic density of states (DOS) near the band edge of the stop band in PCs.
Quite interestingly, it is found that the lasing peaks exhibit an equal space of about 4 nm as shown in Fig. 4(c).This intriguing behavior can be interpreted well based on the Fébry-Pérot resonance.According to the Fébry-Pérot resonance, 25 the resonance length l can be estimated by where n is the refractive index of PCs, λ 1 and λ 2 are wavelengths of multimodes.Our experimental result can be well interpreted when the resonance length l is set equal to two times of the thickness of PCs as shown in Fig. 1(b).Therefore, the obtained lasing behavior is attributed to the slow light, high photonic density of states, and the Fébry-Pérot resonance.

Conclusion
In summary, the stop band of Tb(OH) 3 /SiO 2 PCs for different particle sizes was observed in a wide range, from UV to red.Utilizing this tuning band property, the cavity of different periodicities can be used to assist lasing emissions for multiple transitions of Tb ions.Due to the large density of states near the stop band edge in PCs lasing emissions can be easily obtained.In view of the strong, stable, and narrow emission bands of Tb ions as well as several advantages of SiO 2 monodispersed nanoparticles, the work shown here should be very useful for the development of optoelectronic devices in practical applications.

Fig. 2 (
Fig. 2 (a) Reflectance spectrum of the sample as shown in Fig. 1(a).(b) Band structure calculation of the photonic crystal with 230 nm Tb(OH) 3 /SiO 2 nanospheres.(c) First Bragg stop band of assembled Tb(OH) 3 /SiO 2 PCs versus Tb(OH) 3 /SiO 2 particle size.The straight line represents the prediction according to the Bragg diffraction.Full widths at half maximum of the stop bands are labeled as error bars.

Fig. 3
Fig. 3 Cathodoluminescence spectra of (a) Tb(OH) 3 /SiO 2 nanoparticle powder and (b) assembled Tb(OH) 3 /SiO 2 nanoparticles with a diameter of 230 nm taken at electron acceleration voltage of 10 kV and current of 5 x 10 -9 A.