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Micro light-emitting diodes (μ-LEDs) coupled to color conversion phosphors are among the most promising technologies for future display and artificial light sources. However, current emitters suffer from excessively large particle sizes, preventing micron-scale processability, and/or low stability that hampers the device lifetime. Here, we demonstrate down-conversion μ-LED phosphors based on CsPbBr3 perovskite nanocrystals directly grown inside perfectly sealed mesoporous silica nanospheres (NSs). Key for this advancement is a high-throughput calcination procedure in the presence of K2CO3 as selective pore sealing agent, which simultaneously produces the CsPbBr3 nanocrystals, boosts their emission efficiency to >87%, and perfectly isolates them from the outer environment without causing inter-particle cross-linking or aggregation. This results in size-homogeneous, finely solution-dispersible, ultra-stable, and highly emissive CsPbBr3-SiO2 NSs that fit the technological requirements of photolithographic inks for highly uniform μ-LED color conversion patterns with pixels smaller than 20 μm.

Multicomponent systems consisting of lead halide perovskite nanocrystals (CsPbX 3 -NCs, X = Br, I) grown inside mesoporous silica nanospheres (NSs) with selectively sealed pores combine intense scintillation and strong interaction with ionizing radiation of CsPbX 3 NCs with the chemical robustness in aqueous environment of silica particles, offering potentially promising candidates for enhanced radiotherapy and radio-imaging strategies. We demonstrate that CsPbX 3 NCs boost the generation of singlet oxygen species ( 1 O 2 ) in water under X-ray irradiation and that the encapsulation into sealed SiO 2 NSs guarantees perfect preservation of the inner NCs after prolonged storage in harsh conditions. We find that the 1 O 2 production is triggered by the electromagnetic shower released by the CsPbX 3 NCs with a striking correlation with the halide composition (I 3 > I 3−x Br x > Br 3 ). This opens the possibility of designing multifunctional radio-sensitizers able to reduce the local delivered dose and the undesired collateral effects in the surrounding healthy tissues by improving a localized cytotoxic effect of therapeutic treatments and concomitantly enabling optical diagnostics by radio imaging.

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