A novel Ca x Y 3−x Al 5−x Ti x O 12 (0 ≤ x ≤ 2.0) solid solution with garnet structure was synthesized by solid-state reaction technique. Ca 2+ and Ti 4+ substituted for Y 3+ and Al 3+ , respectively. Ca 2+ /Ti 4+ doping reduced the sintering temperature of Ca x Y 3−x Al 5−x Ti x O 12 ceramics to 1450 °C, and it also improved corresponding densification process. Meanwhile, the doping strongly influenced microwave dielectric properties. For the samples sintered at 1550 °C for 3 h, the dielectric constant (ε r ) increased from 7.2 to 34.7 by increasing Ca 2+ /Ti 4+ content, and at the same time the quality factor (Q × f) values increased from 12,000 to 45,200 GHz and then slightly declined to 41,000 GHz. The temperature coefficient of resonant frequency (τ f ) values of these samples increased monotonically from − 40 to + 31 ppm/°C by increasing Ca 2+ /Ti 4+ content. Therefore, Ca x Y 3−x Al 5−x Ti x O 12 solid solution ceramics with x = 1.5 sintered at 1550 °C for 3 h showed optimum microwave dielectric properties: ε r = 32.6, Q × f = 45,200 GHz and τ f = + 7 ppm/°C. Ca x Y 3−x Al 5−x Ti x O 12 (0 ≤ x ≤ 2.0) solid solution ceramics with garnet structure were new promising aluminate ceramics for microwave dielectric application.
Fe 3+ ions as near-infrared (NIR) activators are emerging as an alternative to Cr 3+ . 1–5 However, it is a challenge to develop Fe 3+ -activated NIR phosphors featuring tunable optical properties, high efficiency, and thermal stability. Herein, we present a series of near-unity internal quantum efficiency (IQE), wavelength-tunable and thermal stability NIR-emitting phosphors Sr 2− y Ca y Sc 1− x SbO 6 : x Fe 3+ (S 2− y C y S 1− x S: x Fe 3+ ). Sr 2 ScSbO 6 :1%Fe 3+ (SSS:1%Fe 3+ ) phosphor shows broadband NIR emission at 904 nm and near-unity IQE under excitation at 300 nm. Experimental and theoretical calculation results demonstrate that introduced Ca ions could increase the bandgap value and Debye temperature (Θ D ) of host from E g = 3.702 eV, Θ D = 609 K of y = 0 to E g = 3.801 eV, Θ D = 692 K of y = 2. Significantly, the resultant S 2− y C y S 1− x S:1%Fe 3+ NIR phosphors show wavelength-tunable emission from 904 to 952 nm and high IQE of 84.6%–97.5% as well as enhanced thermal stability ( I 423K / I 298K = 76.9%) of Ca 2 ScSbO 6 :1%Fe 3+ (CSS:1%Fe 3+ ) in comparison with that ( I 423K / I 298K = 70.6%) of pristine sample. We fabricated an NIR light-emitting diodes (LED) device by using CSS:1%Fe 3+ NIR phosphors with ultraviolet LED chip and demonstrated its potential applications in anticounterfeiting, information encryption, and night vision.
危险品化学品经营许可证（带存储）