Temperature-induced phase transitions for stuffed tridymites SrGa 2 O 4 and CaGa 2 O 4

Controlled mechano-luminescence properties of SrGa2O4:Tb3+ co-doping with Dy3+ and Eu3+ ions

Trap-controlled mechano-luminescence (ML) featuring photon emission under mechanical stimuli provides promising applications such as dynamic imaging of force, integrated optical sensing, information storage, and anti-counterfeiting encryption. However, the corresponding emission with a single color still limits the application of ML materials. Here, a trap-controlled ML phosphor of SrGa₂O₄:Tb³⁺ (SGO:Tb³⁺) with a green-emission is investigated with an adjustable ML color. The relationship between ML and thermoluminescence (TL) is verified by co-doping with Dy³⁺ and Eu³⁺ ions for the manipulation of the constructed traps. Accordingly, the as-explored ML phosphor with multicolor output is employed to create encrypted anticounterfeiting patterns, which produces bright and spatially resolvable optical codes under the single-point dynamic pressure of a ballpoint pen. Hence, it provides a new approach to achieve ML with multicolor and gives us an insight into understanding the mechanism of the ML procedure.

Structural Diversity and Incompatibility Induced Complex Phase Formation Behavior in the Stuffed Tridymites Ca1-xSrxGa2O4

Stuffed tridymites AM₂O₄ composed of a condensed MO₄-tetrahedra-based framework have been widely investigated due to their structural diversity and rich physical properties. Herein, the strategy of stuffing mixed Ca²⁺ and Sr²⁺ cations into the [Ga₂O₄]^2- framework in (Ca_1-xSr_x)Ga₂O₄ (CSGO, 0 ≤ x ≤ 1) is utilized to manipulate the phase formation behavior with different structure types at particular annealing temperatures. Five derivatives, including α- and β-CaGa₂O₄, β- and γ-SrGa₂O₄, and new CSGO-type structures, were observed. The distinctive feature of the CSGO-structure is the coexistence of UUDDUD- and UDUDUD-type six-membered rings, where U (up) and D (down) denote the orientations of GaO₄-tetrahedra with respect to the plane grids, in a ratio of 2:1. Single-phase α-Ca_1-xSr_xGa₂O₄ (x < 0.2) and γ-Ca_1-xSr_xGa₂O₄ (x > 0.67) could be obtained at low temperatures. Biphasic regions, including α-Ca_1-xSr_xGa₂O₄/CSGO (0.2 ≤ x ≤ 0.67), γ-Ca_1-xSr_xGa₂O₄/CSGO (0.67 < x ≤ 0.8), and β-Ca_1-xSr_xGa₂O₄/CSGO (0.8 < x < 1), were observed at the intermediate temperature region and evolve irreversibly into the CSGO single-phase region upon elevating the temperature. Moreover, the structure-property relationship of the new CSGO-phase was further studied by doping coordination-sensitive Bi³⁺ activators to advance the development and applications of stuffed tridymites.