Structural phase transitions and photoluminescence properties of Eu³⁺ doped Ca_(2−x)Ba_xLaNbO₆ phosphors

Abstract

Crystal structures of the series of double perovskites Ca(2-x)BaxLaNbO6:Eu(3+) phosphors have been examined by powder X-ray diffraction and Rietveld refinements. Ca2LaNbO6 has a monoclinic (P21/n) and Ba2LaNbO6 has a monoclinic (C2/m) structure. The structural phases of Ca(2-x)BaxLaNbO6:Eu(3+) samples are divided into three sections depending on different Ca/Ba ratios: (1) monoclinic phase (P21/n) as Ca2LaNbO6 in the range of x = 0-0.1, (2) mixed phases containing Ca2LaNbO6 and Ba2LaNbO6 between 0.15 and 1.2, and (3) monoclinic phase (C2/m) as Ba2LaNbO6 for x = 1.4-2. Eu(3+) ions act as the structural probes to study the structural phase transitions, and the evolution of the photoluminescence properties and thermal stability behaviours has been also comparatively investigated depending on different structural symmetries from Ca2LaNbO6 to Ba2LaNbO6 phase. The strong red emission from (5)D0-(7)F2 peaking at 618 nm can be found in Ca2LaNbO6:Eu(3+) phosphors, which is attributed to the low crystal field effect of the activator ions located in the highly distorted [LaO8] polyhedra sites. The composition-optimized phosphors can find applications in white light emitting diodes (LEDs).

Probing crystal structure and site‐selective photo‐physical properties of various Eu3+‐doped niobates

“…The ionic size of La being slightly larger than Ca drives the Ca ion to occupy B‐site. La cation completely occupies A‐site is in concurrence with other perovskites containing Ca and La . The refined crystal structures for BLMN and BLCN are given in Table .…”

“…La cation completely occupies A-site is in concurrence with other perovskites containing Ca and La. 11,21,22 The refined crystal structures for BLMN and BLCN are given in Table 1.…”

“…Although cations Nb 5+ have outer electronic configuration 4d 0 , which is chemically inert due to completely vacant ‘d’ orbital, it acts as good activator and host lattice elements . Recently, photoluminescence study has been widely studied in Nb 5+ niobates . The multi cationic sites in the niobates‐based double perovskite of formula A 2 BB'O 6 gives more control for tuning red electric dipole (ie, 5 D 0 → 7 F 2 transition at ~ 615 nm) and orange magnetic dipole (ie, 5 D 0 → 7 F 1 transition at ~ 595 nm) transitions of Eu 3+ ion by changing its local site occupancy in the crystal structure.…”

“…10 Recently, photoluminescence study has been widely studied in Nb 5+ niobates. [11][12][13] The multi cationic sites in the niobates-based double perovskite of formula A 2 BB'O 6 gives more control for tuning red electric dipole (ie, 5 D 0 → 7 F 2 transition at ~ 615 nm) and orange magnetic dipole (ie, 5 D 0 → 7 F 1 transition at ~ 595 nm) transitions of Eu 3+ ion by changing its local site occupancy in the crystal structure. This will effectively control the color characteristics and the color purity of the phosphor materials help to design new phosphor materials with desired emitting colors with the same dopant ion.…”

Energy transfer, tunable luminescence, and thermal stability of Tb3+–Sm3+-codoped Na3Bi(PO4)2 phosphors

“…Eu 3? ions have been regarded as excellent red-emitting activators in many phosphors owing to its 5 D 0 -7 F J (J = 0, 1, 2, 3, 4) transitions [6][7][8]. Sm 3?…”