The dielectric properties of a Ga-based melilite type ceramic Sr 2 Ga 2 SiO 7 via theoretical prediction based on far-infrared spectroscopy and experimental measurement by the Hakki–Coleman method were studied in this work. Dense and single-phase ceramics were fabricated via solid-state reaction at 1330°C and exhibited comprehensive microwave dielectric properties ( ε r ∼ 7.6, Q × f ∼ 23 600 GHz, and τ f ∼ −35.2 ppm/°C) at 14.3 GHz. Chemical modifications were proposed to adjust the thermal stability and reduce the densification temperature. By adding 10 mol% CaTiO 3 , the negative τ f can be compensated to a near-zero value of −3.8 ppm/°C. The densification temperature was reduced to 940°C by adding 3 wt.% LiF. A patch antenna was designed using Sr 2 Ga 2 SiO 7 ceramic with a high radiation efficiency of 99.1% and a gain of 2.788 dBi at the center frequency of 4.371 GHz. All results indicate that the Sr 2 Ga 2 SiO 7 ceramic has promising application potential for 5G wireless communication technology.
Various optical signals are popularly harnessed to realize anticounterfeiting, encryption, and photoluminescence (PL)-based sensing. However, most phosphors can only achieve single PL output under a fixed excitation, thus simultaneous attainment of multimodal PL behaviors remains an imperative pursuit. Herein, a highly integrated multimodal photon-, temperature-, and mechanically responsive Sr2Ga2SiO7:Zn2+/Er3+/Pr3+(SGS:Zn/Er/Pr) is designed/synthesized via a facile solid-state reaction, endowing tunable down/up-converted (DC/UC) PL, mechanoluminescence (ML), and long-persistent PL (LPL) owing to the synergistic effects of self-activated and dopant-induced electronic transitions. serves as both an emitter and a trap center for the self-(L)PL located at ∼468 nm under λex = 267 nm. These behaviors are further optimized by adjusting the content of and by forming a bridge () between trap levels upon Zn2+ incorporation. The excitation and Zn2+ content-dependent PL can be modified from blue to cyan via conflating dual self-PL from the 4T1 → 4A1 transition of Ga3+ at ∼402 nm and . The green DC/red UC PL from Er3+is observed under λex = 357 and 980 nm, respectively. Nonequivalent substitution of Pr3+ at the Sr2+site and the incorporation of Zn2+ can adjust the charge transfer band energy level position and optimize the trap distribution, achieving long-term storage and highly repeatable/efficient LPL/ML generation. Based on abundant PL multimodes, the single-phased SGS:Zn/Er/Pr shows promising applications in sophisticated anticounterfeiting and latent fingerprint detection. Concurrently, owing to the coupled energy levels 2H11/2/4S3/2 of Er3+and the pressure-dependent ML of Pr3+, the SGS:Zn/Er/Pr is also suitably applied as a temperature/stress sensing agent.
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