Crystal-Site Engineering Control for the Reduction of Eu³⁺ to Eu²⁺ in CaYAlO₄: Structure Refinement and Tunable Emission Properties

Abstract

In this article, Eu-activated CaYAlO4 aluminate phosphors were synthesized by a solid-state reaction. Under UV light excitation, characteristic red line emission of Eu(3+) was detected in the range of 570-650 nm. In addition, we introduced crystal-site engineering approach into the CaYAlO4 host through incorporation of Si(4+)-Ca(2+) to replace Al(3+)-Y(3+), which would shrink the AlO6 octahedrons, accompanied by the expansion of CaO9 polyhedron, and then enable the partial reduction of Eu(3+) to Eu(2+). The crystal structure and underlying mechanism have been clarified on the basis of the Rietveld refinement analysis. The PL spectra of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) exhibit both green emission of Eu(2+) (4f(6)5d(1)-4f(7), broadband around 503 nm) and red-orange emission of Eu(3+) ((5)D0-(7)F1,2, 593 and 624 nm) under UV light excitation with a quantum yield of 38.5%. The CIE coordinates of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) phosphors are regularly shifted from (0.482, 0.341) to (0.223, 0.457) with increasing x, which would expand the application of Eu. Furthermore, this investigation reveals the correlations of structure and property of luminescent materials, which would shed light on the development of novel phosphors suitable for lighting and display applications.

Influence of phase transformation on luminescence properties of CaSiN2 with Eu doping

“…In order to figure out the reason of low PL intensity of cubic CaSiN 2 :Eu, XPS was applied to confirm the ionic states of Eu in CaSiN 2 as shown in Figure . According to the published reports, the binding energy of Eu 2+ 3d 3/2 and 3d 5/2 are around 1155 and 1126 eV, respectively, while the binding energy of Eu 3+ 3d 3/2 and 3d 5/2 are around 1165 and 1135 eV, respectively . In our samples, the Eu 2+ 3d 3/2 , 3d 5/2 and Eu 3+ 3d 3/2 , 3d 5/2 configurations were clearly observed, which are in conformity with reports.…”

Insight into a novel rare‐earth‐free red‐emitting phosphor Li3Mg2NbO6:Mn4+: Structure and luminescence properties

“…There are four types of distinctive cation sites in the LMN unit cell. 39,40 As a result, the incorporation of Mn 4+ into the LMN host may induce defects such as V .. These isolated octahedrons share edges with adjacent ones, constructing the three-dimensional rock salt structure, which provides multiple suitable sites for Mn 4+ doping.…”

Multiple‐response anti‐counterfeiting realized in CaYAl3O7 host with the dual coexistence of Eu2+/Eu3+

“…Especially, europium is the most widely used activator, which exhibits the property of valence fluctuation of divalent (Eu 2+ ) and trivalent (Eu 3+ ). Eu 3+ ions emit red emission due to the characteristics of 5 D 0 ‐ 7 F J (J = 0, 1, 2, 3, 4) transitions, while Eu 2+ ions present tunable color ranging from blue to red due to their 5d‐4f transition . Herein, the coexistence of Eu 2+ and Eu 3+ ions suggests a dual‐mode optical output, which would provide the possibility for multi‐dimensional anti‐counterfeiting application.…”