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This review provides a comprehensive discussion on the microwave-assisted synthesis of various materials for photoluminescence and photocatalytic applications. In the past decade, because of its ability to synthesize nanomaterials through faster, cleaner and more cost-effective routes compared to conventional heating, microwave techniques have gained significant importance for the synthesis of metal oxides, fluorides, sulphides, and quantum dots. Additionally, due to the uniqueness of its heating mechanism, the synthesis of materials in various nanostructured forms through microwave-assisted methods has been of great interest and is widely pursued. The materials thus synthesized have been applied as sensing elements in gas sensors, luminescent nanoprobes in bioimaging, materials in fuel cells and solar cells and as photocatalysts for water treatment and energy harvesting. This review describes and discusses their optical and photocatalytic performance in detail, emphasizing on the reaction parameters employed and the structural and morphological properties obtained.

Octahedrally and tetrahedrally connected Mo-O complexes in two different crystal phases were comparatively investigated. The material Ba2YMoO6:Eu3+ exhibits the cubic perovskite structure for which the Mo-O groups are coordinated octahedrally, while BaY2(MoO4)4:Eu3+ has a monoclinic crystal phase for which the Mo-O complexes are connected tetrahedrally. The photoluminescence (PL) excitation spectra show that, the intensity, position and shape of the charge transfer (CT) transitions in the two different materials depended strongly on the surrounding environment. The PL emission properties of Ba2YMoO6:Eu3+ and BaY2(MoO4)4:Eu3+ phosphors as a function of various doping content of Eu3+ ions excited at different wavelengths were explored in detail. The critical concentration of Eu3+ and the critical distance between Eu3+ ions, as well as the concentration quenching effects were discussed. The absolute quantum yield for the monoclinic phase BaY2(MoO4)4:Eu3+ phosphor was about an order of magnitude higher than that of the cubic phase Ba2YMoO6:Eu3+ phosphor.

A series of Tm2−xWO6:xEr3+ (where x = 0.02–0.50 mol) phosphors were synthesized successfully by the solid-state reaction method. The powder X-ray diffraction patterns of the Tm2−xWO6:xEr3+ phosphors confirmed that the as-synthesized materials belonged to the monoclinic crystalline structure, which has a P2/c (13) space group. Due to a similar ionic size and valence state of the Er3+ ions, they can easily replace the Tm3+ in the Tm2WO6 crystal lattice. High-resolution X-ray photoelectron spectroscopy was used to explore the photoelectron binding energy and chemical state of all the elements. The XPS results confirmed that the W atom coordinated octahedrally to the oxygen atoms with its highest 6+ state in the Tm2WO6 material. The upconversion luminescence intensity at 657 nm [4F9/2→4I15/2 (Er3+)], when excited at 980 nm, was enhanced with higher magnitude when increasing the doping concentration from 0.02 mol to 0.20 mol of Er3+ ions. The dependence of the laser pump power with respect to the upconversion luminescence intensity depicts that the emission at 657 nm is due to a single-photon absorption process, and the possible reasons for the number of photons involved in the excitation of the emitting state, n ≤ 1 were discussed. The Commission Internationale del'Eclairage chromaticity coordinates and decay time measured for the Tm2WO6:Er3+ phosphors were investigated. Real-time latent-fingerprint detection using Tm2WO6:Er3+ upconversion phosphor without using Yb3+ ion showed an excellent marking agent for applications in forensic science and medical diagnostics.