Self‐Activated Vanadate Compounds Toward Realization of Rare‐Earth‐Free Full‐Color Phosphors

Abstract

Rare-earth-free phosphors based on vanadate compounds were investigated, where the vanadates included chloride vanadates (M II 2 VO 4 Cl), pyrovanadates (M II 2 V 2 O 7 ), orthovanadates (M II 3 (VO 4 ) 2 ) with divalent cations M II of Mg, Sr, Ba, and Zn, and oxofluorovanadates (A I VOF 4 ) with an alkali metal A I . A chloride pyrolysis method and a liquid phase precipitation method were proposed for preparing the chloride vanadates and pyro-and orthovanadates, respectively. These vanadate compounds showed self-activated photoluminescence (PL) based on the VO 4 clusters against the ultraviolet (UV) light irradiation. The colors of PL covered almost the whole visible-light region from blue to yellow as Sr 2 VO 4 Cl (deep blue), Ca 2 VO 4 Cl (sky blue), Ba 2 V 2 O 7 (green), Sr 2 V 2 O 7 (yellowish green), Zn 3 (VO 4 ) 2 (yellow), and Mg 3 (VO 4 ) 2 (yellow). A correlation was suggested from these compounds between the luminescent colors and the structural feature as the longer V-O distances in the VO 4 tetrahedra in the crystal structures led to the longer wavelength in PL. This seemed to be also applicable for the oxofluorovanadates A I VOF 4 (A I = K and Cs) which contain the VOF 4 polyhedra with one O 2ion and four Fions as the ligands, as they exhibited the reddish PL.

The determining factor of the luminescence energies of vanadate phosphors

“…The single crystalline grains of Ba 2 V 2 O 7 were grown from the melt. 51) The Ba 2 V 2 O 7 powder precipitated in the aqueous solution 44) was heated at 1100°C for 24 h and, then, cooled to 600°C at 6°C/h. The product was actually a mixture of crystallographic phases of Ba 2 V 2 O 7 and Ba 3 (VO 4 ) 2 as suggested in the phase diagram 52) and Ba 2 V 2 O 7 grains were selected by checking the lattice constants with XRD before collecting the diffraction intensity data.…”

“…An empirical relationship was suggested between the luminescent colors and the composition types as blue with M 2 VO 4 Cl (M = Ca and Sr), green with MB 2 V 2 O 7 (MB = Sr and Ba), and yellow with MBB 3 (VO 4 ) 2 (MBB = Mg and Zn). 44) Reddish PL was observed in AVOF 4 (A = K and Cs). On the other hand, the theoretical basis had not been revealed before this work.…”

“…1). 44) It should be noted that the VO 4 tetrahedra in the crystal structures commonly act as the luminescent centers in those vanadate phosphors, or VOF 4 in the fluorovanadates. The emission colors vary from deep-blue to red depending on the composition.…”

Improvement of self‐activated luminescence from introduced cation disorder in Sr6V2O11

“…Rare earth ion (RE)‐ or self‐activated phosphors have been widely investigated in engineering applications and basic sciences . Self‐activated phosphors present some advantages such as broad emission band, RE free, low sintering temperature, environment‐friendly (sintering in air), low cost, etc.…”

“…Rare earth ion (RE)-or self-activated phosphors have been widely investigated in engineering applications and basic sciences. [1][2][3][4][5][6] Self-activated phosphors present some advantages such as broad emission band, RE free, low sintering temperature, environment-friendly (sintering in air), low cost, etc. For example, self-activated vanadate is efficient luminescence material and has been paid considerable attention on solid-state lighting and display.…”