New double perovskite Cd2MgTeO6:Sm3+, Na+ tellurate phosphors with abnormal thermal quenching for applications in white and plant growth lighting

New Sm3+ doped Cd2MgTeO6 tellurate red-emitting phosphors with Na+ ions as charge compensation were obtained using a high-temperature solid-state approach at 1000 °C. During this study, the prepared phosphors were subjected to phase purity, particle morphology, luminescence characteristics, thermal stability, and Commission Internationale de L′ Eclairage (CIE) chromaticity. The critical quenching concentration of Sm3+ doped Cd2MgTeO6 phosphor was 2 mol%. According to Dexter's theory and the calculated Rc value (22.21 Å), the dipole-dipole interaction causes the phenomenon of concentration quenching. Particularly, the Cd2MgTeO6:2 mol%Sm3+, 2 mol%Na+ phosphor exhibited an evident red-light emission (647 nm) at λex = 407 nm because of the 4G5/2 to 6H9/2 level transition of Sm3+. Its internal quantum efficiency (IQE) was 38.87%. It is worth noting that the Cd2MgTeO6:Sm3+, Na+ phosphor exhibited abnormal thermal quenching (ATQ) characteristics, and the luminous intensity of the Cd2MgTeO6:2 mol%Sm3+, 2 mol%Na+ increased by 7.20% at 480 K compared with the initial temperature. In addition, white LEDs and red LEDs were successfully manufactured with a 408 nm chip. The prepared red LED showed the emission spectrum similar to the absorption spectrum of Phytochrome Pr, which is expected to be applied in plant growth. The w-LED had a CCT (correlated color temperature) of 4790 K, color rendering index of 91, and color coordinates of (0.348, 0.335). Therefore, the Cd2MgTeO6:Sm3+, Na+ phosphor has demonstrated potential applications in w-LEDs and plant growth LEDs.