Inorganic Luminescent Materials: 100 Years of Research and Application

Abstract

Luminescent materials (or phosphors) are generally characterized by the emission of light with energy beyond thermal equilibrium. More vividly this means: The nature of luminescence is different from that of black-body radiation. Luminescence can occur as a result of many different kinds of excitation, which is reflected in expressions such as photo-, electro-, chemi-, thermo-, sono-, or triboluminescence. In practice, most often the excitation is via X-rays, cathode rays, or UV emission of a gas discharge. The role of the phosphor is to convert the incoming radiation into visible light. In addition to the type of excitation, two other terms are used quite often to classify luminescent materials. Both can be related to the decay time (s): fluorescence (s < 10 ms) and phosphorescence (s > 0.1 s). [1] The luminescence of inorganic solids, which is the focus of this contribution, can be traced to two mechanisms: luminescence of localized centers and luminescence of semiconductors (Fig. 1). [1,2] The first case is represented by transitions between energy levels of single ions (e.g., f±f transitions of Eu 3+ in Y 2 O 3 :Eu 3+ ) or complex ions (e.g., the charge-transfer transition on [WO 4 ] 2± in CaWO 4 ). In the case of luminescent centers, the transition rate is (more or less strongly) correlated to the relevant quantum-mechanical selection rules, and reflected in the intensity as well as the decay time of the transition. Excitation and emission can be (as shown in Fig. 1) both localized to one center (e.g., [WO 4 ] 2± in CaWO 4 ) or separated from each other: excitation on sensitizer (e.g., Ce 3+ in LaPO 4 :Ce 3+ ,Tb 3+ ) is followed by emission on activator (e.g., Tb 3+ in LaPO 4 :Ce 3+

Ligand field density functional theory for the prediction of future domestic lighting

“…[1][2][3][4][5] The application relevance of this issue is related to the functioning of lanthanide ions in light emitting diodes (LED) in order to generate domestic lighting. Nowadays, the ban on the incandescent light bulbs being effective, artificial white light source is, for instance, obtained by the combination of a gallium nitride blue LED with an inorganic phosphor, i.e.…”

Structural and photoluminescent properties of the MgGa2O4:Co2+ ceramic compound revisited after two decades

“…Particularly, the cobalt ion is found in several oxidation states (+2, +3, and +4) and in distinct crystal environments, but the divalent state is well known by its capacity to generate luminescence in the visible and infrared regions [10][11][12]. From the point of view of the energy level structure, the divalent ion d 7 in tetrahedral coordination presents a level splitting similar to the d 3 ion's level splitting in octahedral coordination, where the ground level is the 4 A 2 ( 4 F) and the first excited energy levels are 4 T 2 ( 4 F), 4 T 1 ( 4 F), and 4 T 1 ( 4 P) for small values of Dq/B [9]. In the absence of spin-orbit coupling, only the 4 T 2 ( 4 F)→ 4 A 2 ( 4 F) transition is detected in the visible region, with the appearing of a broad and intense emission band, due to the fact that the 4 T 2 ( 4 F) energy level is strongly dependent on the crystal field parameter Dq, generating a spin-allowed transition.…”

“…In the scientific literature, it is possible to find several works concerning the photoluminescent properties of optical systems doped with transition metals [3,4,9]. Cobalt is one of the transition metals exhibiting luminescent properties when inserted in ceramic hosts.…”

“…This causes a direct impact on the production cost, with raw material economy resulting in optimized financial costs, also being environmentally friendly. Transition metals and rare earth doped materials exhibit such features, being widely used in several applications as solid-state lasers [1,2], scientific research [3,4], medicine and dosimetry [5][6][7], and sensing and optical communications [8], just to name a few examples.…”

Hydrothermal synthesis and photoluminescence properties of cerium-doped cadmium tungstate nanophosphor

“…Luminescent materials in the form of nanobelt, nanoparticles, nanorods, nanowires, and nanotubes are of interest not only for basic research, but also for fascinating applications. [1,2] Divalent metal ion tungstates are of interest for their luminescent properties [3] and metal tungstates have good application prospects in scintillators, optical fibres, microwave applications, humidity sensors, photoluminescence materials, and catalysts, etc. [4][5][6][7] Most of the tungstates have scheelite structure or wolframite mainly depending on their cationic radii.…”