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Self-activated phosphors are capable of generating optical emissions from the internal ion groups of host lattice before externally introducing luminescent ions. However, numerous self-activated phosphors only show luminescence at low temperature due to the thermally activated energy migration among ion groups at room temperature, severely confining their application conditions. In this letter, we propose a strategy to converting the low-temperature luminescence to a room-temperature one through changing the synthesis conditions to induce structural distortions and thus to limit energy migration. Room-temperature self-activated luminescence of Ca2Nb2O7 was accordingly achieved in submicroplates synthesized using the sol–gel method. By further coupling the blue broadband emission from Ca2Nb2O7 submicroplates with the characteristic luminescence of Ln3+ (Pr3+, Sm3+, and Dy3+) dopants, multicolor emissions were successively tuned through adjusting the concentration of Ln3+. Our results are expected to expand the scope of designing room-temperature self-activated phosphors and tuning multicolor emission.

Color manipulation of intense multiluminescence from CaZnOS:Mn2+ has been realized by adjusting Mn2+ concentration. Not only the photoluminescence (PL) of Mn2+ emission from 4T1(4G) to 6A1(6S) shows a red shift from yellow to red with increasing Mn2+ concentration, which is in contrast to the fixed PL emission reported by Hintzen et al. (Chem. Mater., 2009), but also mechanoluminescence (ML) and cathodoluminescence (CL) have a similar variation. More attractively, the brightness of multiluminescence is surprisingly intense for all the CaZnOS:Mn2+ with a large-scale Mn2+ doping (0.1–10 mol %). Based on the investigation of crystal field, various spectral results, and PL lifetimes, the red-shift mechanism of multiluminescence reported here has been proposed to arise from the exchange interaction effect of Mn2+ pairs at higher concentrations. In addition to correcting the previous misunderstanding on the emission of CaZnOS:Mn2+, these findings extend the tunable emission window, opening up new opportunities ...

The quantum confinement in atomic scale and the presence of interlayer coupling in multilayer make the electronic and optical properties of 2D materials (2DMs) be dependent on the layer number (N) from monolayer to multilayer. Optical properties of 2DMs have been widely probed by several optical techniques, such as optical contrast, Rayleigh scattering, Raman spectroscopy, optical absorption, photoluminescence, and second harmonic generation. Here, it is reviewed how optical properties of several typical 2DMs (e.g., monolayer and multilayer graphenes, transition metal dichalcogenides) probed by these optical techniques significantly depend on N. Further, it has been demonstrated how these optical techniques service as fast and nondestructive approaches for N counting or thickness determination of these typical 2DM flakes. The corresponding approaches can be extended to the whole 2DM family produced by micromechanical exfoliations, chemical-vapor-deposition growth, or transfer processes on various substrates, which bridges the gap between the characterization and international standardization for thickness determination of 2DM flakes.