We report for the first time dual-wavelength lasing
at 78 K in a vertical cavity containing ultrasmooth MAPbCl3 single
crystals. To understand this unusual lasing behavior, the MAPbCl3
single crystals were thoroughly investigated in terms of temperature-
dependent optical experiments. Microreflectivity measurements
reveal, besides the standard exciton feature at the ∼385 nm
orthorhombic bandgap, an additional previously unreported
excitonic peak at ∼412 nm. This second exciton feature aligns
with the second lasing line, strongly suggesting the coexistence of a
“second phase” within the primary orthorhombic lattice. We show
that this second phase persists up to 300 K and is likely associated
with the quantum dot-like nanostructures detected on the surface
of the MAPbCl3 crystals. The second phase depends on the growth method and crystal size but is likely traceable in all MAPbCl3
systems. These insights offer enhanced understanding of the MAPbCl3 system and open new pathways for blue-UV photonic