Microwave-Assisted Preparation of Luminescent Inorganic Materials: A Fast Route to Light Conversion and Storage Phosphors

Abstract

Luminescent inorganic materials are used in several technological applications such as light-emitting displays, white LEDs for illumination, bioimaging, and photodynamic therapy. Usually, inorganic phosphors (e.g., complex oxides, silicates) need high temperatures and, in some cases, specific atmospheres to be formed or to obtain a homogeneous composition. Low ionic diffusion and high melting points of the precursors lead to long processing times in these solid-state syntheses with a cost in energy consumption when conventional heating methods are applied. Microwave-assisted synthesis relies on selective, volumetric heating attributed to the electromagnetic radiation interaction with the matter. The microwave heating allows for rapid heating rates and small temperature gradients yielding homogeneous, well-formed materials swiftly. Luminescent inorganic materials can benefit significantly from the microwave-assisted synthesis for high homogeneity, diverse morphology, and rapid screening of different compositions. The rapid screening allows for fast material investigation, whereas the benefits of enhanced homogeneity include improvement in the optical properties such as quantum yields and storage capacity.

Review— On the Development of Phosphors for Luminescent Materials: Synthesis, Characterization, Applications and Evolution of Phosphors as White-Light-Emitting Diodes

“…One such range of microwaves primarily utilized wireless telecommunication protocols including Bluetooth and Wi-Fi modems. 100 Microwave industrial and residential applications emanate from their potential to heat substances based on their dielectric properties. 101 The characteristics of microwave irradiation differ dramatically from those of traditional heat generation methods.…”

Modulating trap distribution of persistent phosphors upon simple microwave-assisted solid-state reactions

“…For MASS reaction, 10 g of powdered activated charcoal was used as the microwave susceptor [34,35,36] . Two alumina crucibles were used, including a bigger volume crucible (30 mL) to hold charcoal and a smaller one (5 mL) to place 0.4 g of the starting mixed precursors.…”

“…Finally, the samples were retrieved and no thermal treatment was made afterwards. The temperature profile of the microwave heating process follows a rapid temperature increase in a short period of time [36] . These parameters were found to be highly reproducible from a number of trials.…”

Engineering aluminosilicate's photochromism by quantum chemistry

“…Hence, the sum of all the knowledge acquired on these minerals converges toward the idea that it is possible to play both on their structure and composition to tune all three main photochromic properties-activation, color, and bleaching. These minerals can be artificially synthetized, 14 as already shown by Weller et al or Lastusaari and coworkers whose work is more than significant. 4,11 The aim of this work is, using Density Functional Theory (DFT) and its time-dependent version (TD-DFT) methods, to access all three main photochromic properties (activation, F-center's absorption, and bleaching energies) of sodalite type materials for which we vary the composition or the structure.…”