Metallic (Cum)n+ quantum nanoclusters through the lithium metaphosphate network: Efficient energy transfer to Mn2+ ions for white LED

Abstract

Metallic (Cum)n+ nanoclusters are superior to their (Aum)n+ and (Agm)n+ counterparts in the aspect of being relatively cheap for wide industrial demands. However, further improvements are still needed, especially in terms of the generation of (Cum)n+ nanoclusters. Herein, (Cum)n+ has been successfully generated with Mn2+ ions into 2.5MnO·47.5Li2O·50P2O5 (MnP), 2.5CuO·47.5Li2O·50P2O5 (CuP) and 2.5MnO·2.5CuO·45Li2O·50P2O5 (CuMnP) matrices. This generation has been demonstrated by XRD, XPS, TEM, SEM, AFM, UV–Vis and PL analyses. MnP displays an amorphous nature with red light emission under an excitation wavelength of 409 nm due to the 4T1(G)→6A1(S) transition of Mn2+ ions. CuP and CuMnP exhibit the formation of spherical nanoclusters with a size less than 10 nm. These nanoclusters are attributed to (Cum)n+, which exhibit tunable emission from blue to white to red light as the excitation wavelength changes from 270 to 360 nm. When MnP, CuP and CuMnP are subjected to 380 °C for 4, 1 and 1 h, respectively, the LiPO3 crystalline phase has evolved. This is associated with the reduction of (Cum)n+ to plasmonic (Cu°)n nanoparticles, and therefore crystallization-induced photoluminescence weakening. This demonstrates that the lithium metaphosphate glassy matrix provides an efficient emission as compared to the corresponding LiPO3 crystalline phase. Overall, in the CuMnP matrix, there is an efficient energy transfer from (Cum)n+ to Mn2+ as the 1Eg excited level of (Cum)n+ is higher than the 4A1/4E energy levels of Mn2+ ions. This synergistic Mn2+/(Cum)n+ combination has resulted in the generation of a rare earth-free platform promised for white LED applications.