Tam Nguyen Kieu

The molten salt synthesis (MSS) method was used to effectively prepare green phosphors BaAl1.4Si0.6O3.4N0.6:Eu2+ (or BSON:Eu2+) via one homogeneous sphere-like morphology utilizing NaNO3 in the form of the reacting agent. The phosphors produced one wide stimulation spectrum between 250 and 460 nm, as well as a significant green emission has a maximum point at 510 nm owing to the 4f65d1-4f7 (8S7/2) shifts for Eu2+ ions. With illumination under 365 as well as 450 nm, the ideal discharge strengths for the specimen prepared utilizing melted salt would receive a boost of 17% and 13%, surpassing the specimen prepared utilizing the traditional solid-state reaction (SSR) approach. The abatement of concentration for the ions of Eu2+ from BSON:Eu2+ is 5 mol%. In addition, the interactivity of dipole-dipole would be the cause of said abatement. Heat abatement would be studied utilizing the formation coordinate method with abatement temperature reaching ∼200 oC. Elemental mapping as well as power-dispersing X-ray spectroscopy (EDS) spectra demonstrated that the expected BaAl1.4Si0.6O3.4N0.6:Eu2+ materials were formed.

To enhance the dual-layer remote phosphorus configuration’s color standard help spread its application in the LED devices, the new green-emitting phosphor of Ca7Si2P2O16:Eu2+ is proposed. The sol-gel method is used to dope the Eu2+ ions with Ca7Si2P2O16. Increasing the ion Eu2+ concentration can lead to high thermal stability, color-tunable ability, stronger green emission band, and higher photoluminescence extraction. The dual-layer structure’s color standards, as well as the luminous flux, are examined with different concentrations of Ca7Si2P2O16:Eu2+ in the phosphor layer. Owing to the improved features, the green phosphor Ca7Si2P2O16:Eu2+ has enhanced the emission intensity in the blue and green wavelengths, resulting in better color mixing and distribution. The luminescence shows the enhancement when increasing the concentration of Ca7Si2P2O16:Eu2+. However, the color rendering feature can present a reduction with more than 10% wt. green phosphor within the double-layer phosphorus remote configuration, due to color balance’s loss.

In this paper, we consider the physical layer security of a downlink cooperative multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) network over Nakagami-m fading. The network consists of a multi-antenna source, multiple decode-and-forward (DF) relays, and two users with different priority, in the presence of a passive eavesdropper. Specifically, we investigate the secure transmission from the source to the users via the help of the relays, in which the signals of the users might or might not be successfully decoded at the relays. Thus, we aim to design secure communication protocols for the considered system, where transmit antenna selection (TAS), maximal ratio transmission (MRT), and relay selection are employed based on the source-to-relays channel conditions. To characterize the secrecy performance, analytical and asymptotic expressions for the secrecy outage probability (SOP) of the overall system are derived. Our analytical results validated by Monte-Carlo simulations show that the secrecy performance of cooperative NOMA networks can be improved by increasing the number of antennas at the source and the number of relays. Comparing TAS and MRT, we conclude that TAS has lower complexity but can achieve the secrecy performane comparable with MRT. Finally, the results also indicate that our proposed protocol bring more general and practical insights with similar secrecy performance compared with the conventional solution.

In this paper, we study the physical layer security of a downlink multi-input single-output non-orthogonal multiple access (NOMA) system, in which transmit antenna selection (TAS) scheme, users’ quality of service (QoS) requirements, Nakagami-m fading channel, and user selection solution are considered for secure NOMA transmission. Specifically, we investigate the scenario that a base station (BS) (source) communicates with two legitimate user (LU) clusters with different priority depending on their QoS requirements in the presence of multiple passive eavesdroppers over Nakagami-m fading. To enhance the secrecy performance, we examine a TAS scheme and a user selection method. In this context, prior to transmission, a transmit antenna and a user in high-priority LU cluster are jointly selected to maximize the channel quality of the link from the BS to the selected user. Furthermore, together with the selected high-priority user, a user in low-priority LU cluster, which has the best channel condition, is chosen for performing two-user NOMA. In order to evaluate the secrecy performance, tight and asymptotic closed-form expressions of secrecy outage probability for selected LUs and overall system are derived. Our theoretical results confirmed by Monte–Carlo simulation show that in QoS-based NOMA system, high-priority users cause the higher effects on the overall secrecy performance in comparison with low-priority users. Finally, these results also indicate that our proposed communication protocol achieves the secrecy performance greater than conventional protocol.