Introduction In recent years, all-inorganic halide perovskite (CsPbX3, X=Cl, Br, I) quantum dots (QDs) have attracted widespread attention due to their excellent optical and electrical properties. They exhibit high photoluminescence (PL) efficiency, narrow emission bandwidth and tunable emission energy at a wide spectral range. However, the poor stability of CsPbX3 QDs under ambient conditions strongly limit their applications. In this work, CsPbI3 QD-doped borosilicate glasses were prepared by high-temperature melting-quenching followed by heat treatment. ZrO2 is employed as the network modifier, which effectively modifies the local network structure of glass. By optimizing the concentration of ZrO2 and the heat treatment temperature or time, the PL efficiency of the glass can be effectively improved. PL intensity of the QDs glass sample demonstrates high stability, which is almost unchanged after multiple heating and cooling cycles between 293 K and 373 K.
Methods The CsPbI3 QD-doped glasses were prepared by high-temperature melting-quenching followed by heat treatment. All raw materials with the designed ratios were accurately weighed and mixed in an agate mortar for 20 min. After the raw materials were thoroughly mixed, they were placed in a covered alumina crucible and transferred to a muffle furnace for melting at 1200 ℃ for 20 min. Afterwards, the glass melt was quenched onto a steel plate and pressed into a glass plate. Finally, the precursor glass were heat-treated at different temperatures (520–550 ℃) for 4 h and at 530 ℃ for different times (2–12 h) to precipitate the CsPbI3 QDs.
PL spectra, PL decay curves and thermal stability of glass samples were examined with a FLS 980 fluorescence spectrometer.Optical absorption spectra were recorded by using a UV-3600UV-Vis-NIR spectrometer. X-ray diffraction patterns were recorded by using an X’Pert PRO powder diffractometer. The network structure of glass was analyzed by using a Nicolet 6700 spectrometer and an InVia Reflex Raman spectrometer. The photoluminescence quantum yield (PLQY) was measured with an absolute PLQY measurement system.
Results and discussion From the XRD results, as the heat treatment time increases, two diffraction peaks at angles (2θ) of 28.5° and 35.5° become stronger in intensity, corresponding to the (200) and (211) planes of CsPbI3 QDs, respectively. With increasing the ZrO2 concentration, the diffraction peak of (200) crystal plane shifts to a larger angle, which is attributed to the replacement of larger Pb2+ ions by smaller Zr4+. Based on FTIR and Raman spectra characterizations, the network structure of glass is mainly composed of [BO4], [SiO4] and [BO3] units. As the ZrO2 concentration increases, the fraction of tetrahedral network structure formed by [BO4] and [SiO4] units in the glass increases, leading to an increase in the fraction of the three-dimensional network structure of the glass, therefore inhibiting the crystallization of CsPbI3 QDs and reducing the size of QDs. This results in the blue shift of the absorption edge and emission peak wavelength. From the emission spectra, with increasing the ZrO2 concentration, the PL intensity of the glass samples first increases and then decreases. Both the absorption edge and emission peak wavelength show a clear redshift with increasing the heat treatment temperature or time, which is mainly attributed to the increased size of QDs. According to the PL decay curves, as the ZrO2 concentration increases, the PL lifetime of glass gradually decreases; as the heat treatment temperature increases,the PL lifetime of glass gradually increases. Finally, after multiple heating and cooling cycles at 293–373 K, there was no significant decrease in the PL intensity of the glass.
Conclusions The CsPbI3 QD-doped borosilicate glass was prepared successfully by high-temperature melting-quenching followed by heat treatment. X-ray diffraction shows that CsPbI3 QDs are precipitated in the glass. With increasing the ZrO2 concentration, the PL intensity of the glass samples first increases and then decreases, and the highest PLQY reaches 32.6%. In addition, the emission peak wavelength and absorption edge show a blue shift, which is attributed to the increased fraction of tetrahedral network structures formed by [BO4] and [SiO4] units in the glass at higher ZrO2 concentrations. Consequently, the increase in the fraction of the three-dimensional network structures of the glass impedes the movement of Cs+, Pb2+ and I–, inhibiting the crystallization of CsPbI3 QDs. After multiple heating and cooling cycles at 293–373 K, there was no significant decrease in the PL intensity of the glass,indicating that Zr4+ doped CsPbI3 perovskite QDs glass has good thermal stability, which may find applications in display, lighting and other fields.