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.

Organic room temperature phosphorescence (RTP) materials have drawn increasing attention due to their unique features, especially the long emission lifetime for applications in biomedicine. In this review, we provide an overview of the recent developments of organic RTP materials applied in the biomedicine field. First, we introduce the basic mechanism of phosphorescence and subsequently we present various strategies of modulating the lifetime and efficiency of room temperature organic phosphorescence. Next, we summarize the progress of organic RTP materials in biological applications, including bioimaging, anti‐cancer and antibacterial therapies. Finally, we provide an outlook with regard to the challenges and future perspectives in the field.

It is an enormous challenge to achieve highly efficient organic room‐temperature phosphorescence (RTP) with a long lifetime. We demonstrate that, by bridging the carbazole and halogenated phenyl ring with a methylene linker, RTP phosphors CzBX (X=Cl, Br) present high phosphorescence efficiency (ΦPh). A ΦPh up to 38 % was obtained for CzBBr with a lifetime of 220 ms, which is much higher than that of compounds CzPX (X=Cl, Br) with a C−N bond as a linker (ΦPh<1 %). Single‐crystal analysis and theoretical calculations revealed that, in the crystal phase, intermolecular π‐Br interactions accelerate the intersystem crossing process, while tetrahedron‐like structures induced by sp3 methylene linkers restrain the nonradiative decay channel, leading to the high phosphorescence efficiency in CzBBr. This research paves a new road toward highly efficient and long‐lived RTP materials with potential applications in anti‐counterfeiting or data encryption.