Rare earth (RE) ions doped Al2O3 transparent ceramics have been studied for decades for optical applications due to many excellent properties, including high strength, high thermal conductivity, high transparency in the visible and up to the IR range; and stable chemical composition and structure [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. For example, highly transparent Dy3+-doped polycrystalline alumina ceramics were prepared with the real in-line transmittance (RIT) up to 55% (at λ=632nm), and the photoluminescence (PL) emission spectra under 350 nm excitation revealed the presence of a very broad band emission ranging from 370 to 600 nm and centered at 420 nm [1]. Transparent Eu3+-doped (0.05–0.15 at.%) alumina ceramics with fine-grained microstructure were prepared and studied in terms of optical properties and photoluminescence [2]. Transparent bulk polycrystalline Nd3+: Al2O3 was prepared by a powder processing route in conjunction with single-step CAPAD reaction/densification, the emission bandwidth of Nd3+: Al2O3 is broad of ∼13 THz, which can be lead to the development of lasers [6]. Nd2O3 doped Al2O3 translucent ceramics with near infrared (NIR) emission were fabricated using the conventional solid-state reaction and vacuum sintering for high power laser operation [7]. Er3+, Eu3+ or Nd3+ doped transparent Al2O3 ceramics prepared by a combination of wet shaping technique (slipe casting), pressure less pre-sintering, and hot isostatic pressing (HIP) method was designed as a promising material for LED applications [9]. Tb3+ doped transparent Al2O3 ceramics prepared by spark plasma sintering (SPS) had exciting prospects for high energy laser technology [10]. Compared with other RE ions, Nd3+ ions have strong absorption at ∼808 nm wavelength matching well with the emission of commercial LD, which enables device miniaturization and high laser efficiency [14], [15].

In the work of Gui et al. [9], commercial 808 nm LD was used as an excitation source, and near-infrared emission peaked at 1054 nm was achieved in the as prepared Nd3+: Al2O3 translucent ceramics. However, many other impurity emissions peaked at ∼1058 nm, ∼1105 nm, ∼1168 nm, ∼1229 nm, ∼1240 nm, ∼1272 nm, ∼1334 nm, ∼1376 nm and 1470 nm had been observed. However, the emission intensities were too low to apply. And due to second phase and great grans caused by high dopant, it is well known that adding the required amount of dopant inevitably results in inclusions, which will strongly deteriorate the transparency and result in concentration quenching. Therefore, it is a challenging topic to prepare high transparent Al2O3 ceramics with strong luminous performance. And it is not a feasible method to improve the emission properties by just increasing the concentration of active ions in Al2O3.

Encouragingly, in our previous research, it is revealed that with 0.05 wt%Zn2+ co-doped, the near-infrared emission of Yb3+/Er3+ doped Al2O3 transparent ceramics are enhanced by ∼10 times [16]. It inspires us to prepare Nd3+: Al2O3 transparent ceramics co-doped with Zn2+ to improve the luminous performance.

Based on the above researches, in the present work, Nd3+: Al2O3 transparent ceramics co-doped with Zn2+ were prepared in the same method of Gui et al. [7]. And the effects of dopant concentrations of Zn2+ on the structure and optical properties were investigated.