Luminescent Materials with Advanced Properties and Applications

Luminescent materials have attracted significant attention due to their exceptional properties, which have been widely used in various fields such as sensing [1,2,3], bioimaging [4,5,6], catalysis [7,8,9], and optoelectronics [10,11,12]. Synthesis strategies for luminescent materials include the hydro/solvothermal method and microwave-assisted synthesis, as well as low-energy sustainable preparation strategies [13,14,15]. The structural design and optical control of luminescent materials are current research hotspots, promoting the sustained development of luminescent materials in a wide range of fields.

This Special Issue covers various luminescent materials that are currently a focus of research, such as carbon dots, perovskites, metal complexes, lanthanide phosphors, and luminescent hybrid materials, exploring their photophysical properties and achieving promising applications in chemical sensing and photocatalysis.

Advanced synthesis technology can stimulate the design and development of high-performance luminescent materials. Our group [16] developed a kind of Schiff base strategy to achieve room-temperature synthesis of carbon nanoclusters. The proposed carbon nanoclusters display a unique property of dual-exciting central emission. These nanoclusters can act as dual-channel fluorescence nanoprobes for the reliable determination of hemin based on an inner filter effect. Furthermore, Maltsev’s group [17] prepared a transparent single crystal (Er³⁺,Yb³⁺:GdMgB₅O₁₀) with a size of up to 24 × 15 × 12 mm through a high-temperature solution growth technique using dipped seeds. Laser operation in continuous-wave mode can be achieved, and the maximal output power is up to 0.15 W, with a slope efficiency of 11%.

Carbon dots, as a new type of luminescent carbon nanomaterial, exhibit fascinating optical properties. Yin’s group [18] utilized amine-rich soybean flour (nitrogen source) and lemon juice (acidic medium) to improve the luminescent efficiency of carbon quantum dots. The enhanced quantum yield is attributed to the fact that the obtained carbon quantum dots undergo a thorough hydrothermal reaction and have zwitterionic surfaces. Meanwhile, the carbon quantum dots can be used for the specific detection of Cr(VI) ions, with a detection limit of 8 ppm. Like nitrogen-doping, sulfur-doping can also regulate the electronic structure of carbon dots. In light of this, Yu’ s group [19] developed blue-emitting S, N-co-doped carbon dots by using hydrothermal methods, achieving the rapid and sensitive detection of baicalein with a detection limit of 33 nM by means of static quenching and an inner filter effect.

Luminescent hybrid materials show superior photophysical properties by integrating the properties of different structural units. Ito’s group [20] synthesized inorganic–organic hybrid phosphors by means of the hybridization of Eu³⁺-containing polyoxometalate anions with bolaamphiphile surfactants. The proposed phosphors display a characteristic red emission originating from Eu³⁺ ions, with a lifetime in the order of milliseconds. Meanwhile, the emission intensity of the phosphors is laser-power-dependent, and the emission intensity increases linearly as the excitation laser power rises. Moreover, hybrid structures can also achieve efficient photocatalytic activity because the heterojunctions with an intimate interface can promote photogenerated charge transfer. Wang’s group [21] constructed biochar-supported cadmium sulfide composites for photocatalytic hydrogen production. The composites can achieve a photocatalytic hydrogen production rate of up to 7.8 mmol·g⁻¹·h⁻¹, which is about 3.69 times higher than that of cadmium sulfide without biochar.

The regulation of photophysical properties is a key focus of research in luminescent materials. Xia’s group [22] studied the effect of organic spacer cations on the optical properties of quasi-two-dimensional perovskite. An organic spacer with short chain length can greatly reduce the quantum confinement and dielectric confinement in perovskite. Considering the impact of synthetic conditions on the structural properties of materials, Lee’s group [23] investigated their effect on the optical properties of Si-substituted CaYAlO₄:Eu. The use of ball milling can reduce the particle size and induce surface defects in Al₂O₃, and the ratio of the charge transfer band to f-f transition increases as the ball milling time increases. On the contrary, the variation in aluminum precursors has a negligible impact on the quantum efficiency of CaYAlO₄:Eu. Metal–organic coordination is also a powerful strategy for adjusting optical properties. Malandrinos’s group [24] studied the influence of organic ligands on the optical properties of silver complexes. Different ligands can significantly regulate the quantum efficiency (11–23%) of silver complexes. Interestingly, the solid-state luminescence behavior of silver complexes is obviously different from that in a solution. In contrast, Urriolabeitia’s group [25] explored the influence of Pd coordination on the photophysical properties of (Z)-4-hetarylidene-5(4H)-oxazolones complexes. Their results show that the coordination of Pd²⁺ ions with 4-hetaryliden-5(4H)-oxazolone does not cause, in these cases, an increase in fluorescence intensity.

Therefore, the articles collected in this Special Issue report on the most pressing issues in the field of luminescent materials, such as the development of advanced synthesis technologies, the construction of novel luminescent materials, and the regulation of photophysical properties.