Enhancing oxygen/moisture resistance of quantum dots by short-chain, densely cross-linked silica glass network

Abstract

Quantum dots (QDs) are facing significant photoluminescence degradation in moisture environment. In QDs-silicone composites, the poor water resistance of silicone matrix makes it easy for water and oxygen molecules to erode QDs. To tackle this issue, we proposed a new QDs protection strategy by introducing short-chain silica precursors onto the QDs’ surface, so that a dense silica passivation layer could be formed onto the QDs nanoparticles. Sol-gel method based on 3-aminopropyl triethoxysilane (APTES), 3-mercaptopropyl trimethoxysilane (MPTMS), and 3-mercaptopropyl triethoxysilane (MPTES) were adopted to prepare the uniform and crack-free QDs-silica glass (QD-glass). Because of the crosslinking of short-chain precursors, the formed silica glass possesses 38.6% smaller pore width and 68.6% lower pore volume than silicone, indicating its denser cross-linked network surrounding QDs. After 360-hour water immersion, the QDs-glass demonstrated a 6% enhancement in red-light peak intensity, and maintained a stable full width at half maximum (FWHM) and peak wavelength, proving its excellent water-resistant ability. However, the conventional QDs-silicone composites not only showed a decrease of 75.3% in red-light peak intensity, but also a broadened FWHM and a redshifted peak wavelength after water immersion. QDs-glass also showed superior photostability after 132-hour exposure to blue light. Red-light peak intensity of QDs-glass remained 87.3% of the initial while that of QDs-silicone decreased to 19.8%. And the intensity of QDs-glass dropped to 62.3% of that under 20 ℃ after thermal treatment of 160 ℃. Besides, under increasing driving currents, the light conversion efficiency (LCE) drop of QDs-glass is only one fifth that of QDs-silicone. Based on the QDs-glass, the white light-emitting diodes was achieved with a high luminous efficiency (LE) of 126.5 lm/W and a high color rendering index (CRI) of 95.4. Thus, the newly proposed QD-glass has great significance in guaranteeing the working reliability of QDs-converted devices against moisture and high-power environment.

Direct Optical Patterning of Quantum Dots: One Strategy Different Chemical Processes

“…At the photophysical level, the effect of the oxygen and water in the scQDs can be resumed as reported by Yang et al in Figure 6 [40]. In this view, the core/shell scQD when prepared can have just a few defect states (DS) (depending upon the optimization of the chemical synthesis) meaning that the scQDs have a determined PL emission, FWHM, and PLQY, function of size and composition (valence and conductive band) (Figure 6a).…”

“…For ambient conditions we mean the effect of the oxygen, moisture and working temperature on the functional characteristics of the scQDs, i.e. emission wavelength, luminescence broadening, photoluminescent quantum yield (PLQY) [40], and PL intermittency (blinking) [41] [42]. What is clear is that the role of oxygen, moisture, and temperature and their combination with light is crucial as highlighted in different reports testing the stability of the QDs used for display [43], solar cells [44], and fluorescent probes for biology [45].…”

Direct Optical Patterning of Quantum Dots: One Strategy, Different Chemical Processes

“…At the photophysical level, the effect of the oxygen and water in the scQDs can be resumed as reported by Yang et al in Figure 6 [ 46 ]. In this view, the core/shell scQDs, when prepared, can have just a few defect states (DS) (depending upon the optimization of the chemical synthesis), meaning that the scQDs have a determined PL emission, FWHM, and PLQY, function of size and composition (valence and conductive band) ( Figure 6 a).…”

“…For ambient conditions, this means the effect of the oxygen, moisture, and working temperature on the functional characteristics of the scQDs, namely: the emission wavelength, the luminescence broadening, the photoluminescent quantum yield (PLQY) [ 46 ], and the PL intermittency (blinking) [ 47 , 48 ]. What is clear is that the roles of oxygen, moisture, and temperature, and their combination with light, are crucial, as highlighted in different reports testing the stability of the QDs used for display [ 49 ], solar cells [ 50 ], and fluorescent probes for biology [ 51 ].…”

“… Scheme of the photophysical processes involving the scQDs ( a ) when they are excited with light; ( b ) under the presence of a limited amount of oxygen and water; or ( c ) in the continuous presence of them. (Reprinted with permission from [ 46 ]). …”