The steady and dynamic properties are comparatively investigated for the n-doped and non-doped InGaN LEDs. The simulated results show that the n-doped LED exhibits the superior luminescence and modulation performance, which is mainly attributed to the higher carrier radiative rate of n-doped LED. The results can explain the reported experimental results perfectly.
Silver nanoprisms (AgNPs) affect the performance of organic solar cells (OSCs) in different ways depending on their positions in the device. To investigate this issue, we incorporate AgNPs in different positions of OSCs and compare their performance. The power conversion efficiency (PCE) is improved by 23.60% to 3.98% when the AgNPs are incorporated in front of the active layer. On the other hand, when AgNPs are incorporated in the back of the active layer, the short-circuit current density (JSC) is improved by 17.44% to 10.84 mA/cm2. However, if AgNPs are incorporated in the active layer, both open-circuit voltage (VOC) and JSC are decreased. We discuss the position effect on the device performance, clarify the absorption shadow and exciton recombination caused by AgNPs, and finally indicate that the optimal position of plasmonic AgNPs is in front of the active layer.
Lithium lutetium fluoride (LiLuF4) single crystals doped with different Dy3+ ion concentrations were grown by Bridgman method. The Judd-Ofelt (J-O) strength parameters (Ω2, Ω4, Ω6) of Dy3+ in LiLuF4 crystal are calculated according to the measured absorption spectra and the J-O theory, by which the asymmetry of the Dy3+:LiLuF4 single crystal and the possibility of attaining stimulated emission from 4F9/2 level are analyzed. The capability of the Dy3+:LiLuF4 crystal in generating white light by simultaneous blue and yellow emissions under excitation with ultraviolet light is produced. The effects of excitation wavelength and doping concentration on chromaticity coordinates and photoluminescence intensity are also investigated. Favorable CIE coordinates, x=0.319 3 and y=0.349 3, can be obtained for Dy3+ ion in 2.701% molar doping concentration under excitation of 350 nm.
An efficient post-coding strategy is proposed in this letter to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals for optical intensity modulated direct detection (IM/DD) systems. The post-coding scheme based on discrete cosine transform (DCT) is employed after the inverse fast Fourier transform (IFFT) in the transmitter to reduce the PAPR of OFDM signals. This method is different from the conventional pre-coding scheme which is employed before IFFT operation. Numerical simulations demonstrate that the new DCT post-coding strategy can significantly reduce the PAPR than the conventional pre-coding scheme. Meantime, the bit error rate (BER) performance of the proposed post-coding system can be improved compared with the conventional pre-coding scheme.