Symmetry Inhomogeneity of Ca_9–xZn_xEu(PO₄)₇ Phosphor Determined by Second-Harmonic Generation and Dielectric and Photoluminescence Spectroscopy

Abstract

A series of Ca 9−x Zn x Eu(PO 4 ) 7 phosphates (0 ≤ x ≤ 1) with a β-Ca 3 (PO 4 ) 2 -type structure was successfully synthesized and studied. Three areas of compositions, I (0 ≤ x ≤ 0.5), II (0.5 < x ≤ 0.8), and III (0.8 < x ≤ 1), were distinguished. In these regions the unit cell parameters and the full width at half-maximum (FWHM) of reflexes in the X-ray diffraction patterns change monotonously. The fracture in these dependences was observed on the frontiers between regions I/II and II/III. The limits of these areas were determined by second-harmonic generation (SHG), dielectric, and photoluminescence spectroscopy methods. It was shown that in Ca 9−x Zn x Eu(PO 4 ) 7 the Eu 3+ cations occupy low-symmetry sites. With an increase in of Zn 2+ concentration, the structure symmetry changes from noncentrosymmetric (space group (SG) R3c) to centrosymmetric (SG R3̅ c). In this case, the distortion of europium polyhedra in the structure increases and, as a result, the luminescence intensity rises. It was found that in β-Ca 3 (PO 4 ) 2 -type solid solutions by replacing Ca 2+ with Zn 2+ the luminescence intensity can be finely tuned. Measured quantum yields (QY) reach 65%. It can be concluded that centrosymmetric phases show higher luminescence intensity. This method of property management may be common for β-Ca 3 (PO 4 ) 2 -type structure phosphors, since the host matrix is very sensitive to changes in composition.

Co-Doping Effect of Mn2+ and Eu3+ on Luminescence in Strontiowhitlockite Phosphors

“…In the Sr3Eu(PO4)3, only one site was observed, with an average Eu-O distance of approximately 2.6754 Å. This point was clearly demonstrated in previous studies [23,60], where it was shown that for the 5 D0 → 7 F0 transition, the Eu-O distance has a direct correlation with the wavelength of the transition. Hence, line A corresponds to the Eu 3+ environment in the Sr3Eu(PO4)3, while line B corresponds to the Eu 3+ in Sr3(PO4)2 (Figure 8b).…”

“…Despite numerous articles on the photoluminescence properties of strontiowhitlockite-type phosphors, the full concentration series with Sr 2+ → M 2+ or Sr 2+ → R 3+ has not been discussed. However, a similar series on Ca-based phosphates, such as Ca 9− x M 2+ x Eu(PO 4 ) 7 , was previously described in detail for M 2+ = Zn 2+ [ 23 ], Mg 2+ [ 24 ], and Mn 2+ [ 25 ].…”

NEW DATA ON LOCAL STRUCTURE FEATURES OF THE SOLID SOLUTION Ca9La(PO4)7(1-x)(VO4)7x:Eu3+(1 %)

“…5). Таким образом, в исследованном твердом растворе наблюдается симметрийная негомогенность, найденная нами ранее [2] в некоторых других твердых растворах на основе -Ca3(PO4)2.…”

Antimicrobial and Cell-Friendly Properties of Cobalt and Nickel-Doped Tricalcium Phosphate Ceramics

“…The PXRD patterns were used to refine the crystal structure. Previously, it was shown that phosphates with the β-TCP structure can have either a polar or non-polar structure with a variety of space groups [55]. Based on the crystal's chemical structure, the observed space groups are:…”