Sub-3 nm Lanthanide-Doped Double Perovskite Quantum Dots: A Multifunctional Platform for Thermal-Enhanced Upconversion Nanothermometry and Magnetic Resonance Imaging

. The successful demonstration of in vivo tumor imaging confirms their potential as effective MRI contrast agents. This study establishes ultrasmall lead-free double perovskite QDs as a versatile multifunctional platform integrating nanothermometry and bioimaging functionalities.