Materials that exhibit X-ray excited luminescence have great potential in radiation detection, security inspection, biomedical applications, and X-ray astronomy [1][2][3][4] . However, such materials are almost exclusively limited to inorganic crystals, which are typically prepared under high temperatures 5 . Herein, we report a design principle of purely organic phosphors to boost X-ray excited luminescence with sufficient utilization of triplet excitons. Our experimental data reveal that proportion of emission from bright triplet excitons is significantly improved upon X-ray irradiation, compared with UV excitation. These organic phosphors have a detection limit of 33 nGy/s, which is 167 times lower than the standard dosage for X-ray medical examinations. We further demonstrated their potential application in X-ray radiography, which can be conveniently recorded using a digital camera. These findings illustrate a fundamental principle to design efficient X-ray excited purely organic phosphors, propelling the development of radioluminescence related applications.X-ray-responsive materials generally display large X-ray attenuation coefficients because of high atomic number elements, which have aroused intense research interest owing to their wide applications in bioimaging, radiotherapy, and non-destructive defect detection of industrial products [6][7][8][9][10] . Such X-ray-responsive materials include non-emissive radiocontrast agents (e.g., iohexol and iopromide) and scintillators that can convert high energy X-ray beam into low-energy visible photons 2,11,12 . To date, almost all reported X-ray-sensitive materials are limited to inorganic phosphors or organometallic materials containing heavy metals 13 . Purely organic materials, also termed as metal-free organic phosphors, have congenital advantages as scintillator candidates, including abundant resources, flexibility, mild preparation conditions, and environmental friendliness. However, weak X-ray absorption and low exciton utilization hinder the development of purely organic scintillators 12 , leaving it a formidable challenge. Purely organic phosphors are mainly made up of light atoms, such as C, H, N, etc., resulting in weak absorbance of X-ray (attenuation coefficient μ ∝Z , Equation S1). Besides, there only exists fluorescence from singlet excitons upon irradiation owing to weak spin-orbit coupling (SOC). In principle, almost all triplet excitons,

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Amorphous purely organic phosphorescence materials with long‐lived and color‐tunable emission are rare. Herein, we report a concise chemical ionization strategy to endow conventional poly(4‐vinylpyridine) (PVP) derivatives with ultralong organic phosphorescence (UOP) under ambient conditions. After the ionization of 1,4‐butanesultone, the resulting PVP‐S phosphor showed a UOP lifetime of 578.36 ms, which is 525 times longer than that of PVP polymer itself. Remarkably, multicolor UOP emission ranging from blue to red was observed with variation of the excitation wavelength, which has rarely been reported for organic luminescent materials. This finding not only provides a guideline for developing amorphous polymers with UOP properties, but also extends the scope of room‐temperature phosphorescence (RTP) materials for practical applications in photoelectric fields.

Provided here is evidence showing that the stacking between triplet chromophores plays a critical role in ultralong organic phosphorescence (UOP) generation within a crystal. By varying the structure of a functional unit, and different on‐off UOP behavior was observed for each structure. Remarkably, 24CPhCz, having the strongest intermolecular interaction between carbazole units exhibited the most impressive UOP with a long lifetime of 1.06 s and a phosphorescence quantum yield of 2.5 %. 34CPhCz showed dual‐emission UOP and thermally activated delayed fluorescence (TADF) with a moderately decreased phosphorescence lifetime of 770 ms, while 35CPhCz only displayed TADF owing to the absence of strong electronic coupling between triplet chromophores. This study provides an explanation for UOP generation in crystal and new guidelines for obtaining UOP materials.

There are few reports about purely organic phosphorescence scintillators, and the relationship between molecular structures and radioluminescence in organic scintillators is still unclear. Here, we presented isomerism strategy to study the effect of molecular structures on radioluminescence. The isomers can achieve phosphorescence efficiency of up to 22.8 % by ultraviolet irradiation. Under X-ray irradiation, both m-BA and p-BA show excellent radioluminescence, while o-BA has almost no radioluminescence. Through experimental and theoretical investigation, we found that radioluminescence was not only affected by non-radiation in emissive process, but also highly depended on the material conductivity caused by the different molecular packing. This study not only allows us to clearly understand the relationship between the molecular structures and radioluminescence, but also provides a guidance to rationally design new organic scintillators.Scintillators are a type of luminescence materials that can convert high energy photons or particles to visible photons, [1] which receive extensive attention in various fields, such as medical imaging [2] and irradiation detecting. [3] To date, scintillators are mainly divided into two categories, inorganic and organic scintillators. Compared with inorganic scintilla-