Bluish-White Luminescence in Rare-Earth-Free Vanadate Garnet Phosphors: Structural Characterization of LiCa₃MV₃O₁₂ (M = Zn and Mg)

Abstract

Extensive attention has been focused toward studies on inexpensive and rare-earth-free garnet-structure vanadate phosphors, which do not have a low optical absorption due to the luminescence color being easily controlled by its high composition flexibility. However, bluish emission phosphors with a high quantum efficiency have not been found until now. In this study, we successfully discovered bluish-white emitting, garnet structure-based LiCaMVO (M = Zn and Mg) phosphors with a high quantum efficiency, and the detailed crystal structure was refined by the Rietveld analysis technique. These phosphors exhibit a broad-band emission spectra peak at 481 nm under near UV-light excitation at 341 nm, indicating no clear difference in the emission and excitation spectra. A very compact tetrahedral [VO] unit is observed in the LiCaMVO (M = Zn and Mg) phosphors, which is not seen in other conventional garnet compounds, and generates a bluish-white emission. In addition, these phosphors exhibit high quantum efficiencies of 40.1% (M = Zn) and 44.0% (M = Mg), respectively. Therefore, these vanadate garnet phosphors can provide a new blue color source for LED devices.

Synthesis and photoluminescence properties of Eu3+-activated LiCa3ZnV3O12white-emitting phosphors

“…In this present work, the x c ¼ 0.02; V ¼ 1926.86Å 3 ; and Z ¼ 8. 52 The critical average distance R c for Eu 3+ ions in LCZV host material was determined to be about 28.44Å. As well-known, nonradiative energy migration among luminescence activators can take place through exchange interaction or multipole-multipole interaction.…”

“…tetrahedral. 45,52 However, due to the low doping concentration of Eu 3+ ions, the absorption peaks of Eu 3+ ions were not observed.…”

Crystal structure, phonon modes, and bond characteristics of AgPb2B2V3O12 (B = Mg, Zn) microwave ceramics

“…All the other cations are occupied in their fixed positions . The position of oxygen in a garnet structure can be deduced using the following equations:Here x , y , and z represent the 96 h site atomic position of an O atom. A , B , and C are the ionic radii of the ions (expressed in Å).…”

“…The bonds V–O in the [VO 4 ] tetrahedra and B–O in the [BO 6 ] octahedra increase slightly with the substitution of Zn 2+ for Mg 2+ ions. A similar behavior, ie, increase in bond length of the tetrahedra and octahedra with the substitution of Zn 2+ for Mg 2+ , was also reported in systems including Ca 5 M 4 (VO 4 ) 6 (M = Zn and Mg) and LiCa 3 MV 3 O 12 (M = Zn and Mg), which is due to the larger ionic radius of Zn 2+ ion.…”

“…At the optimum sintering temperature of 750°C, APMVO shows the maximum bulk density of 5.59 g/cm 3 with the percentage density of 96.3 ± 0.1, while APZVO possesses bulk density of 5.99 g/cm 3 with 94.6 ± 0.1 percentage density at its optimum temperature of 590°C. Usually, ceramics containing Zn 2+ ions are sintered at lower temperatures compared to those containing Mg 2+ ions …”