The Role of Auxiliary Alkali Metal Ions on Scheelite Structure Double Molybdate and Tungstate Phosphors

Abstract

Eu-doped alkali metal double molybdate and tungstate phosphors, (MEu) (Mo,WO) (MEM and MEW, M = Li, Na, and K), have been identified as potential candidate materials for white light-emitting diodes. However, there are no systematic considerations of the role of auxiliary alkali-metal ions (AMIs) on the structural, chemical, and luminescent properties of these phosphors. Here, a systematic investigation to elucidate the role of AMIs on MEM and MEW phosphors was performed using ab initio calculations based on experimental evidence. The results from experimental assessments with intensive structural and chemical bond analyses reveal a clear dependence of AMIs on the structural and luminescent properties of phosphors. The structural changes due to AMIs originate from a bond length change between AMIs-O bonds, and AMIs had minor effects on the other bonds. A phase transition induced by K ions originates from not only structural factors but also local chemical bonding characteristics. Overall, the results indicate that the major role of AMIs is to induce phosphor structural changes, and the effects on the chemical properties are minor. The results of this study shed light on developing not only MEM and MEW phosphors but also new phosphor materials using auxiliary metal ions.

Monoclinic Lu2–xSmxWO6-Based White Light-Emitting Phosphors: From Ground–Excited-States Calculation Prediction to Experiment Realization

“…Therefore, this sample possessed great application potential for near-ultraviolet (n-UV) chip-based LED lighting. Except for experimental investigation, the above-mentioned first-principle ground-state calculation was also employed to reveal the luminescence origin of pure or doped tungstates and molybdates. − For transition metal salts compounds, the valence band and conduction band were principally composed of oxygen 2p states and metal n d states. Thus, their intrinsic emission was ascribed to electrons jumping from n d orbits to 2p orbits.…”

Bond characteristics, mechanical properties, and high‐temperature thermal conductivity of (Hf1−xTax)C composites

“…To interpret the variations in the elastic modulus, we performed Mulliken BOP analysis, which directly indicates the bonding nature of constituent elements . Table lists the bond length and BOP of constituent bonds in (Hf 1−x Ta x )C composites.…”

“…To elucidate the origin of the instability, we calculated the negative COHP, which directly represents electronic instability as well as bonding and antibonding characteristics, depending on the electronic energy. 28,41 Positive and negative population values indicate bonding and antibonding states in the electronic structure, respectively. Figure 3 shows that the Fermi level of HfC is at the edge of the bonding states.…”

“…To interpret the variations in the elastic modulus, we performed Mulliken BOP analysis, which directly indicates the bonding nature of constituent elements. 41,43 covalency in the bonding. The BOPs of the Hf-C and Ta-C bonds show that Ta-C has a higher degree of covalency than Hf-C, regardless of composition.…”

Моделирование твердых растворов NaGd(MoO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=-- NaEu(MoO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=- и Na-=SUB=-2-=/SUB=-Gd-=SUB=-4-=/SUB=-(MoO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=--Na-=SUB=-2-=/SUB=-Eu-=SUB=-4-=/SUB=-(MoO-=SUB=-4-=/SUB=-)-=SUB=-7-=/SUB=- методом межатомных потенциалов

“…Молибдаты в этой большой группе соединений с шеелитовой структурой (в том числе, искаженной) обладают более высокими люминесцентными характеристиками по сравнению с вольфраматами [12]. В качестве молибдатных матриц на основе шеелитов и шеелитоподобных соединений исследовались различные составы, начиная от простых молибдатов, таких как CaMoO 4 и др.…”