Lead halide perovskite nanocrystals (LHP NCs) are attractive for optically-pumped, solution-processed lasers in the visible, owing to their wide spectral tunability, their outstanding optical gain properties and the suppressed non-radiative recombination losses stemming from their defect-tolerant nature. In this work, we demonstrate flexible waveguides combining the transparent, bioplastic, polymer cellulose acetate (CA) with green-emitting CsPbBr₃ or red-emitting CsPb(Br,I)₃ NCs in solution-processed architectures based on polymer-NC multilayers deposited on CA micro-slabs.

Experiments and simulations indicate that the employment of the thin, free-standing CA membranes results in confined electrical fields, enhanced by two orders of magnitude compared to identical multilayer stacks deposited on conventional, thick and rigid quartz substrates. As a result, the polymer structures exhibit improved amplified spontaneous emission (ASE) characteristics under nanosecond excitation, with ASE thresholds down to 95 μJ cm^-2 in the green and 70 μJ cm^-2 in the red and high net modal gain up to 450 cm^-1 and 630 cm^-1, respectively. The optimized gain properties are accompanied by a notable improvement of the ASE operational stability due to the low thermal resistance of the substrate-less membranes and the intimate thermal contact between the polymer and the NCs. Their application potential is further highlighted by the membrane ability to sustain dual-color ASE in the green and red through excitation by a single UV source and the activation of underwater stimulated emission

Lead halide perovskite nanocrystals (LHP NCs) are attractive for optically-pumped, solution-processed lasers in the visible, owing to their wide spectral tunability, their outstanding optical gain properties and the suppressed non-radiative recombination losses stemming from their defect-tolerant nature. In this work, we demonstrate flexible waveguides combining the transparent, bioplastic, polymer cellulose acetate (CA) with green-emitting CsPbBr₃ or red-emitting CsPb(Br,I)₃ NCs in solution-processed architectures based on polymer-NC multilayers deposited on CA micro-slabs.

Experiments and simulations indicate that the employment of the thin, free-standing CA membranes results in confined electrical fields, enhanced by two orders of magnitude compared to identical multilayer stacks deposited on conventional, thick and rigid quartz substrates. As a result, the polymer structures exhibit improved amplified spontaneous emission (ASE) characteristics under nanosecond excitation, with ASE thresholds down to 95 μJ cm^-2 in the green and 70 μJ cm^-2 in the red and high net modal gain up to 450 cm^-1 and 630 cm^-1, respectively. The optimized gain properties are accompanied by a notable improvement of the ASE operational stability due to the low thermal resistance of the substrate-less membranes and the intimate thermal contact between the polymer and the NCs. Their application potential is further highlighted by the membrane ability to sustain dual-color ASE in the green and red through excitation by a single UV source and the activation of underwater stimulated emission