ZnGa 2 O 4 (ZGO) persistent luminescence (PersL) ceramics doped with different concentrations of Cr 3+ were prepared by the co-precipitation method and hot isostatic pressing (HIP) post-treatment. After HIP post-treatment, the ZGO PersL ceramics was significantly improved from opaque to transparent visual appearance due to the elimination of micro-pores during HIP process. The effects of Cr 3+ concentration on the morphology, transmittance and PersL properties of ZGO PersL ceramics were systematically investigated. The ZGO PersL ceramics with higher Cr 3+ dopant concentrations show less micro-pores and higher transmittance, which indicates that the Cr 3+ can also work as a sintering additive to increase the density and to improve the optical quality of ZGO PersL ceramics. The photoluminescence excitation (PLE) and emission (PL) intensities increase with the increase of Cr 3+ concentration up to 0.25 at.%. At yet higher Cr 3+ concentrations, the ZGO PersL ceramics exhibits weaker PL and PLE intensities which is probably caused by the concentration quenching effect. However, the PersL decay curves show that the PersL performance of ZGO ceramics increases with increasing Cr 3+ concentrations, indicating that the doping by Cr 3+ ions may cause another traps formation leading to stronger and longer PersL. The PersL decay curves of all ZGO PersL ceramics were fitted by the second-order exponential function, indicating that at least two kinds of traps with different electron release rates exist in the ZGO ceramics. The influence of Cr 3+ concentration on the thermoluminescence (TL) of ZGO PersL ceramics was also studied, and the results showed that the TL curves of the pre-sintered ceramics shifted to lower temperatures, indicating that the depth of trap related to Cr 3+ ions is shallower than the depth of trap caused by the intrinsic defects.
Xiaoqian Dong,Zhibin Chen,Lehui Liu,Feifei Yuan,Yisheng Huang,Lizhen Zhang,Zhoubin Lin
Broadband near-infrared (NIR) phosphors play a crucial role in the development of next-generation smart NIR light sources based on blue light-emitting diodes (LEDs). The emission bandwidth is an important parameter for evaluating the performance of these phosphors. Herein, an ultra-broadband NIR phosphor CaMgSi 2 O 6 :Cr 3+ (CMSO:Cr), with a tunable emission band and a full width at half maximum (FWHM) ranging from 138 nm to 393 nm, is obtained by adjusting the doping concentration of Cr 3+ . In the low-concentration doped sample, a single emission peak at 785 nm is observed. When the concentration of Cr 3+ exceeds 1.0 at%, emissions at both 785 nm and 980 nm are detected. The emission peak at 785 nm originates from the [MgO 6 ](Ⅰ) octahedron within the CMSO structure. On the other hand, the emission peak at 980 nm is attributed to the presence of a twisted octahedron [MgO 6 ](Ⅱ), which is caused by defects and vacancies resulting from the charge imbalance when Mg 2+ ions are replaced by Cr 3+ ions. The Cr 3+ ion primarily occupies the [MgO6](Ⅰ) site in the lower-concentration doped sample, which explains the photoluminescence peak at 785 nm. With the increase in the concentration of Cr 3+ ions, more and more Cr 3+ ions preferentially occupy the [MgO 6 ](Ⅱ) octahedral sites, leading to the broad emission at 980 nm. A novel NIR phosphor light source was fabricated by combining a blue chip with CMSO:Cr phosphor. Driven by a current of 60 mA, the NIR light output power of 5.89 mW and 0.76 mW is achieved by using CMSO:0.015Cr and CMSO:0.04Cr, respectively. This work demonstrates that new luminescent centers can be generated by substituting heterovalent ions, resulting in broadened emission spectra.
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