A broadband tunable grating-coupled external cavity laser is realized by employing a self-assembled InAs/GaAs quantum-dot （QD） superluminescent diode （SLD） as the gain device. The SLD device is processed with a bent-waveguide structure and facet antireflection （AR） coating. Tuning bandwidths of 106 nm and 117 nm are achieved under a-A and 3.5-A injection currents, respectively. The large tuning range originates essentially from the broad gain spectrum of self-assembled QDs. The bent waveguide structure combined with the facet AR coating plays a role in suppressing the inner-cavity lasing under a large injection current.
ZnO nanorods were grown on Si substrate by hydrothermal method under various reaction time （12, 24, and 36 h）, Zn^2＋ concentrations （0.01, 0.02, and 0.05 mol/L） and reaction temperatures （70-95 ~C）. Their photoluminescence （PL） tests were taken at room temperature. Nanorods grown under longer reaction times or higher temperatures can emit stronger UV light and depressed green light, suggesting better crystallization of ZnO nanorods. Higher Zn^2＋ concentration results in stronger green band emitting, whereas the UV peak is depressed with the Zn^2＋ concentration over 0.02 mol/L. This indicates that excessive interstitial Zn defects may be introduced into the nanorods in Zn-rich environment.
HU Ming,ZHANG Xia,MENG Xianquan School of Physics and Technology,Wuhan University,Wuhan 430072,Hubei,China
GaN thin films grown on sapphire were implanted by Eu^3＋ with three different fluences （5.0×10~14 , 2.5×10~15 and 5.0×10~15cm~–2 ）. The photoluminescence （PL） spectra show that, after annealing, the samples exhibit strong emission at around 622.0 nm under 325 nm laser excitation. The intensity of this emission increases by one order of magnitude after annealing at from 600 ℃ to 900 ℃. Moreover, it increases less than 2 times when the fluence increases from 5×10~14 cm~–2 to 5×10~15 cm~–2 for the sample annealing at 900 ℃. The PL emission peaks around 622 nm of samples annealing at 900 ℃ can be well clarified by Gaussian fitting into 620.2, 622.0 and 625.0 nm, which are due to the Eu^3＋ related with defects, Eu^3＋ occupied at substitutional positions of Ga, and that located at interstitial sites, respectively. It shows that the different microenvironments and positions of Eu^3＋ are responsible for these peaks, and especially the defects introduced by implantation play an important role in the behavior of the PL because they set up an energy transmission bridge from exotic photons to Eu^3＋ .
