Luminescence Properties of CaAl₂O₄:Eu³⁺, Gd³⁺ Phosphors Synthesized by Combustion Synthesis Method

Abstract

CaAl2O4:Eu3+ (1 mol.%) co-doped with varying concentration of Gd 3+ (1, 2, 5, and 10 mol.%) were prepared by combustion synthesis method at 600• C and further annealed at 1000• C. All the compositions were investigated for their structural and photoluminescence properties. It was observed that both states of europium i.e. Eu 3+ and Eu 2+ were present and ratio of these states changes on heating at 1000• C. The materials synthesized at 600• C showed high intense peak around 440 nm due to presence of Eu 2+ and less intense peaks in the red region which were due to presence of Eu 3+ . On annealing the compounds at 1000• C, intensity of peak around 440 nm decreases and intensity of peaks in the red region increases significantly. The 5 D0 → 7 F3 transition due to Eu 3+ at 657 nm appears as the highest intensity peak. All co-doped samples annealed at 1000• C showed the higher intensity than the mono doped sample which is due to energy transfer from the Gd 3+ to Eu 3+ . The second rare-earth ion (Gd 3+ ) acts as sensitizer and enhances the photoluminescence intensity. The X-ray diffraction spectra reveal the monoclinic phase of CaAl2O4 in all the samples which showed that Eu 3+ and Gd 3+ do not change the crystalline structure of calcium aluminate.

Luminescent Properties of (Ca7ZrAl6O18-Ca3Al2O6-CaZrO3):Eu3+ Composite Ceramics and Tracing in the Hydration Process

“…As it was reported elsewhere [36,37], the luminescent properties of the alkaline earth aluminates depend on various factors including the nature, structure, and composition of the matrix, as well as the rare-earth ion content. As it was also reported elsewhere [38,39], both the high degree of similarity between the structures of the Ca 7 ZrAl 6 O 18 and Ca 3 Al 2 O 6 aluminates and the similarity among ionic radii of Ca 2+ (1.26 Å) and Eu 3+ (1.206 Å) make both aluminates promising host lattices for Eu 3+ ions [12]. Going into details, the structure of Ca 3 Al 2 O 6 consists of rings of six AlO 4 tetrahedra ([Al 6 O 18 ]) at eight to a unit cell, surrounding holes with Ca 2+ ions holding the rings together.…”

“…In addition, there are no diffraction peaks of starting substrates or intermediate compounds in the sintered samples; therefore, it is inferred that they were reacted completely. As expected, the significant content of Eu2O3 affects the precipitation of two secondary phases (CaZrO3 and Ca3Al2O6) in all samples, and slight changes were observed in the unit cell parameters of Ca7ZrAl6O18 (Table 1) due to the similar ionic radii of Ca 2+ (1.26 Å) and Eu 3+ (1.206 Å) [12] cations. Similarity among ionic radii of calcium and europium ions makes the Ca7ZrAl6O18 a promising host lattice for the Eu 3+ ion.…”

“…In this regard, lanthanides have been used as substitutes for Ca 2+ in calcium aluminate phases because of the similarities in their spherical shape, ionic radii, and high coordination 2 of 20 numbers. The luminescent properties of calcium aluminates C 12 A 7 [10,11], CA [12][13][14][15][16], CA 2 [17,18], and CA 6 [19,20] doped with Ln 3+ have been intensively studied in recent years, but the role of C 7 A 3 Z in this matter is not known. Following this line of reasoning, it is to be expected that the Eu 3+ ion can easily substitute Ca 2+ in C 7 A 3 Z, as in other calcium aluminates.…”