# Fabrication and Luminescent Properties of Zn-Cu-In-S/ZnS Quantum Dot Films under UV Excitation
## 2 Materials and Methods  
PMMA (poly methyl methacrylate) powder (average Mw \(\sim\)120,000 by gel permeation chromatography) and liquid MMA monomer were purchased from Sigma-Aldrich (St. Louis, MO, USA) and Alfa Aesar (Ward Hill, MA, USA), respectively, both with purities reaching 99%. PMMA and MMA were mixed in a ratio of 1:2.5 [35] in order to produce a slurry, with optimum viscosity for further handling and processing. ZnCuInS/ZnS QDs (PL-QD-CF-530, particle size: 4-5 nm, emission wavelength: 530 \(\pm\) 15 nm, cadmium free, hydrophobic) were purchased from PlasmaChem GmbH (Berlin, Germany), in powder form. Different amounts of QDs (25, 100, 150, and 250 mg) were diluted in 1 mL toluene (Fluka Chemical, Milwaukee, WI, USA), with purity \(>\)99%. The dilution process was facilitated using an ultrasonic bath (TRITON--TR USR070) and a vortex (Velp Scientific ZX3). Furthermore, 1.5 mL of the slurry PMMA/MMA was introduced into the QD solution, followed by vortex stirring. The final product of QD concentration 25, 100, and 150 mg was poured into flexible silicone molds, while the final product of QD concentration 250 mg underwent sonication for five minutes before it was poured into a flexible silicone mold too. Molds filled with the final products were put under vacuum for 15 min to remove entrapped air bubbles from the mixture. Removal of any residual solvent was accomplished by putting the samples in a vacuum oven (Vaciotem T, model 4001489) for 24 h at 50 \({}^{\circ}\)C.  
The produced samples were labeled as QD25, QD100, QD150, and QD250, where the QD number indicates the amount of QD in milligrams within the sample (Table 1). Two experimental configurations were designed for the UV irradiation of the prepared films. Both involved the use of a UV source emitting at 365 nm (Prizmatix multichannel LED light source) and the forward and backward luminescent light was accurately measured by an integrating sphere (Ocean Optics Inc., Micropack Integrating Sphere 50 mm ISP-50-8-R-GT) followed by a grating optical spectrometer (Ocean Optics Inc., HR2000). Figure 1 shows the graphical representation of the forward and backward luminescence light, as well as the reflected and transmitted UV radiation. Measurements were fed into a laptop computer for presentation and further processing. Figure 2a,b shows the experimental configuration for the analysis of the forward luminescent light, as well as the incident UV radiation, that passes through the sample. As shown in Figure 2a, the UV irradiation originates from the UV source, is transmitted through a stabilized flexible optical fiber, and hits the compound film top surface perpendicularly. The distance between the sample and the optical fiber output orifice was carefully adjusted so that the visual pattern of the UV radiation accurately fit the input port orifice of the integrating sphere. Forward luminescent light produced by the sample, as well as the UV radiation that pass through the sample, was then collected by the integrating sphere. A slightly different experimental configuration was used in order to measure the reflected UV radiation, as well as the power of the backward luminescent light. In Figure 2b the output of the LED light source is driven through the optical fiber to the side input port of the integrating sphere. The light entering from the side input port of the integrating sphere is internally driven to hit the sample placed on the top sample port. The integrating sphere collects the backward luminescent light from the sample and the reflected UV radiation and feeds them to the optical spectrometer. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ref.** & **mg QD/mL Toluene** & **\%\%/\% in QD \({}^{*}\)** \\ \hline QD25 & 25 & 1.0 \\ QD100 & 100 & 4.0 \\ QD150 & 150 & 6.0 \\ QD250 & 250 & 10.0 \\ \hline \hline \end{tabular} \({}^{*}\) In the final product, before molding.  
\end{table} 
Table 1: Quantum dot (QD) concentrations along with their values in \(\%\)_av/v_.