Solution-processed　metal-halide　perovskites　hold　great　promise　in　developing　next-generation　low-cost,　high-performance　photodetectors.　However,　the　weak　absorption　of　perovskites　beyond　the　near-infrared　spectral　region　posts　a　stringent　limitation　on　their　use　for　broadband　photodetectors.　Here,　the　rational　design　and　synthesis　of　an　upconversion　nanoparticles　(UCNPs)-perovskite　nanotransducer　are　presented,　namely　UCNPs@mSiO(2)@MAPbX(3)　(X　=　Cl,　Br,　or　I),　for　broadband　photon　detection　spanning　from　X-rays,　UV,　to　NIR.　It　is　demonstrated　that,　by　in　situ　crystallization　and　deliberately　tuning　the　material　composition　in　the　lanthanide　core　and　perovskites,　the　nanotransducers　allow　for　a　high　stability　and　show　a　wide　linear　response　to　X-rays　of　various　dose　rates,　as　well　as　UV/NIR　photons　of　various　power　densities.　The　findings　provide　an　opportunity　to　explore　the　next-generation　broadband　photodetectors　in　the　field　of　high-quality　imaging　and　optoelectronic　devices.