Abs solid, 808nm = Abs solid, 400nm × Abs solution, 808nm Abs solution, 400nm = (0.26±0.03) × (0.072±0.001) (1.4±0.001) = (0.013 ±0.002) Note 2: Calculating percent absorption of 5, 10, 25 mg/mL PbS The 5, 10, and 25 mg/mL films had relatively lower absorption signals than the 50 mg/mL films. To calculate the percent absorption of these films, the percent absorption of the 50 mg/mL film was scaled with the PbS thin film PL emission intensity upon 808 nm excitation of 0.56 W/cm 2 (see equation below). We observed fairly linear change in PbS PL with the change in concentration. The percent absorption of the QD films are reported below. ) fiber coupled 808 nm/447 nm continuous wave lasers with a filter wheel (2) and iris (3). The light is focused onto the UC device (6) at 45-degree angle using an achromatic doublet lens (4) and aspheric lens (5). The UCPL/PL is collected using a plano-convex lens (7) and focused onto a fiber-coupled spectrometer (8, 10). The light is passed through a filter (9) -750nm SP for rubrene/DBP emission, or 850nm LP for PbS emission. The UC device is mounted on an x-stage to ensure the incident light is focused tightly. The spectrometer fiber is mounted on an XYZ stage to maximize the collection efficiency.