Inorganic perovskite lasers are of particular interest, with much recent work focusing on Fabry-Pérot cavity-forming nanowires. We demonstrate the direct observation of lasing from transverse electromagnetic (TEM) modes with a long coherence time ~ 9.5 ps in coupled CsPbBr₃ quantum dots, which dispense with an external cavity resonator and show how the wavelength of the modes can be controlled via two independent tuning-mechanisms. Controlling the pump power allowed us to fine-tune the TEM mode structure to the emission wavelength, thus providing a degree of control over the properties of the lasing signal. The temperature-tuning provided an additional degree of control over the wavelength of the lasing peak, importantly, maintained a constant full width at half maximum (FWHM) over the entire tuning range without mode-hopping.

Diminishing surface defect states in perovskite nanocrystals is a highly challenging subject for enhancing optoelectronic device performance. We synthesized organic/inorganic lead-halide perovskite MAPbBr₃ (MA = methylammonium) clusters comprising nanocrystals with diameters ranging between 20 and 30 nm and characterized an enhanced photoluminescence (PL) quantum yield (as much as ~ 7 times) by encapsulating the MAPbBr₃ with graphene (Gr). The optical properties of MAPbBr₃ and Gr/MAPbBr₃ were investigated by temperature-dependent micro-PL and time-resolved PL measurements. Density functional theory calculations show that the surface defect states in MAPbBr₃ are removed and the optical band gap is reduced by a 0.15 eV by encapsulation with graphene due to partial restoration of lattice distortions.