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X-ray detectors need to be operated at as low as possible doses to reduce radiation health risks during x-ray security examination or medical inspection, which drives the efforts to explore novel detectors with high sensitivity and low detection limits. Organolead trihalide perovskite is the champion, with the highest sensitivity and lowest detection limit. Unfortunately, these materials threaten the safety of the human body and environment by the toxic issue of lead. Here we present a new environmentally friendly material with van der Waals heterostructure of BixIy for ultra-sensitive x-ray detection. The BixIy detector provides anisotropic x-ray detecting performance with a sensitivity up to 1.3×105 µC Gy− 1 cm− 2 and a detection limit as low as 34 nGy s− 1. Meanwhile, our BixIy detector demonstrates wonderful environmental and hard radiation stabilities. Our discovery inspires the search for new van der Waals heterostructure classes to realize high-performance x-ray detectors and other optoelectronic devices without employing toxic elements.

The effective detection of X-ray radiation with low threshold is essential to many medical and industrial applications. Three-dimensional (3D) organolead trihalide and double perovskites have been shown to be suitable for direct X-ray detection. However, the sensitivity and stability of 3D perovskite X-ray detectors are limited by ion motion, and there remains a demand to develop green and stable X-ray detectors with high sensitivity and low detection limit. The emerging low-dimensional perovskites have shown promising optoelectronic properties, featuring good intrinsic stability and reduced ion migration. Inspired by this, we show that our 2D layered perovskite-like (NH4)3Bi2I9 device provides unique anisotropic X-ray detecting performance with different crystal directions, effective suppression of ion migration and a low detection limit of 55 nGyair s−1. These results will motivate new strategies to achieve a high-performance X-ray detector by utilizing 2D layered perovskite or perovskite-like materials, without requiring toxic elements. Perovskite-like materials enable different X-ray detection performance along different crystal directions. A low detection limit of 55 nGyair s−1 is demonstrated.

This paper reports the up-conversion emission properties of alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions under 650 nm pumping using a low power xenon lamp source. Two UV emission bands which centered at 349 nm for the 1I6 → 3F4 transition of Tm3+ ion and at 367 nm for the 1D2 → 3H6 transition of Tm3+ ion and two blue emission bands which centered at 457 nm for the 1D2 → 3H4 transition of Tm3+ ion and at 485 nm for the 1G4 → 3H6 transition of Tm3+ ion have been observed. The up-conversion emission follows a two-photon absorption process for both blue bands, and the UV band centered at 367 nm but follows a cross-relaxation process for the UV band centered at 349 nm. The concentration quenching effect is relatively low in this material under 650 nm pumping. Due to the back energy transfer from Yb3+ to Tm3+ ions, the intensity of UV emission corresponding to the 1I6 → 3F4 transition of Tm3+ ion is stronger in alumina sol samples containing both Tm3+ and Yb3+ ions than in which containing only Tm3+ ions.

This paper reports the dynamic characteristics of sequential energy transfer up-conversion processes in Ybsup3+/sup/Ersup3+/sup:SrMoOsub4/subcrystal. A general method based on the emission intensity has been developed to calculate the nonradiative decay rate. A new macroscopic theory has been developed to calculate the energy transfer parameters based on the crystal structure. According to both new calculating methods, the spectral parameters of Ybsup3+/sup/Ersup3+/sup:SrMoOsub4/subcrystal were calculated, such as up-conversion luminescent quantum efficiencies and threshold pump powers. Both calculating methods may be applied to calculate the spectral parameters of the laser crystal materials.

This paper reports the dynamic characteristics of sequential energy transfer up-conversion processes in Yb3+/Er3+:SrMoO4 crystal. A general method based on the emission intensity has been developed to calculate the nonradiative decay rate. A new macroscopic theory has been developed to calculate the energy transfer parameters based on the crystal structure. According to both new calculating methods, the spectral parameters of Yb3+/Er3+:SrMoO4 crystal were calculated, such as up-conversion luminescent quantum efficiencies and threshold pump powers. Both calculating methods may be applied to calculate the spectral parameters of the laser crystal materials.