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Quantum dots keep their glow under heat after dual modification
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Add as preferred source Quantum dots are semiconductor crystals only a few nanometers in size. Their ability to produce bright, precisely tunable colors has made them promising materials for light-emitting diodes, displays, solar cells and other optoelectronic technologies. Yet heat remains a major obstacle to their practical use.
A study from Koç University demonstrates that modifying both the internal crystal lattice and the surface of perovskite quantum dots can substantially improve their thermal stability. While untreated quantum dots began to lose their structural integrity and light emission at around 60°C (140°F), the modified materials remained brightly emissive and retained their cubic structure at temperatures of up to 80°C (176°F).
The open-access study, published in Nanoscale , was conducted by Pouriya Naziri, Saba Sepahban Shahgoli, Hadi Jahangiri and Professor Umut Aydemir of Koç University.
The researchers focused on cesium lead iodide, or CsPbI₃, quantum dots. These nanocrystals possess attractive optical and electronic properties, particularly for red and near-infrared applications. However, their crystal structure is inherently unstable and can deteriorate when exposed to heat, light or environmental conditions.
As their structure changes, defects can form within the material and on its surface. These defects create pathways through which absorbed energy is lost as heat instead of being released as light—a process known as nonradiative recombination. Surface molecules that help stabilize the nanocrystals can also detach at elevated temperatures, accelerating degradation.
To address these interconnected problems, the Koç University team combined two strategies: replacing a small proportion of the lead atoms in the crystal lattice with cobalt or silver and passivating the quantum dots' surfaces with a mixture of chloride and iodide ions.
The researchers synthesized pristine CsPbI₃ quantum dots alongside cobalt- and silver-doped versions. They then examined how the materials responded to temperatures ranging from 20°C to 80°C (68°F to 176°F).
A range of structural and optical techniques—including X-ray diffraction, transmission electron microscopy, photoluminescence spectroscopy, time-resolved photoluminescence, ultraviolet-visible absorption spectroscopy and Fourier-transform infrared spectroscopy—was used to track changes in the samples.
The untreated CsPbI₃ quantum dots showed signs of lattice distortion and pronounced emission quenching above approximately 60°C (140°F). Heating softened the crystal lattice, promoted surface-ligand loss and created defects that diverted energy away from light emission.
The cobalt- and silver-modified quantum dots responded differently. Both preserved their cubic morphology, showed less particle aggregation and maintained stronger, better-defined light emission up to 80°C (176°F). The modifications therefore expanded the material's thermal stability window by approximately 20 °C.
Measurements of the excited-state lifetime showed that thermally activated nonradiative recombination increased much less in the modified materials. Compared with the untreated quantum dots, the rise in the nonradiative recombination rate was reduced by more than 60%.
Silver-doped quantum dots demonstrated the greatest structural stability. Their lattice spacing expanded by only about 0.6% during heating, compared with approximately 1.5% for the untreated and cobalt-doped samples. They also exhibited the smallest heat-induced narrowing of the electronic bandgap.
The findings indicate that the two modifications perform complementary functions. Replacing some lead atoms with cobalt or silver strengthens the crystal lattice and limits thermal expansion. Halide passivation, meanwhile, reinforces the surface and helps prevent the formation of iodine vacancies and other defects.
This increased resilience could support the development of more durable perovskite-based optoelectronic materials. Heat is generated during the operation of LEDs, displays and other light-emitting devices, meaning that materials must retain their optical performance under repeated warming and cooling cycles.
The study investigated quantum dots at the material level rather than incorporating them into a complete device. Further research will therefore be needed to determine whether the improved stability translates into longer operational lifetimes in LEDs, solar cells and other applications under continuous use and real-world conditions.
Nevertheless, the results provide a practical design principle for improving thermally sensitive perovskite nanocrystals: reinforce the lattice from within while protecting the surface against defect formation.
Pouriya Naziri et al, Probing thermal stability in CsPbI 3 quantum dots with coupled Pb-site doping and halide passivation, Nanoscale (2026). DOI: 10.1039/d5nr04997k
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