Introduction CsPbBr3 perovskite quantum dots have attracted wide attention to be a novel luminescent materials due to their excellent luminescence characteristics. It shows high quantum efficiency (more than 90%) and narrow full width at half-maximum of about 15–20 nm. However, it’s sensitive to water, oxygen, and light, due to its inherent ionic properties and low formation energy.The preparation of CsPbBr3 quantum dot by in-situ crystallization in glass is thus considered to be one of the effective strategies to improve its stability. This work adopts borosilicate as the glass matrix to explore its effect on the glass network structure by changing the molar ratio of CaO/MgO. A further study reveals that there exists regulatory effect on the crystallization behavior and luminescence performance of CsPbBr3. The potential application of the investigated material in the field of optical filters is also explored.
Methods A series of CsPbBr3 quantum dot glasses were prepared by the traditional melt quenching-heat treatment method with varying the ratio of CaO/MgO. The obtained glasses were named CAx, where x represents content of CaO. According to the exact ratio, the raw materials are weighed, fully ground in the mortar for 30 min to uniformity. The mixed powder was transferred to a corundum crucible, following with thermal treatment at 1 200 ℃ for 10 min. Subsequently, the melt material was poured into a preheated graphite mold and annealed for 3 h to release the thermal stress until to room temperature. The transparent precursor glass, named PG, was obtained. CsPbBr3 quantum dot glass was obtained by heat treatment of the precursor glass at different temperatures (450?510 ℃) for 10 h. Finally, the prepared CsPbBr3 quantum dot glass was cut, polished, or ground into a powder for further characterization and use.
Results and discussion With the increase of the CaO/MgO molar ratio, the average particle size of CsPbBr3 quantum dots gradually decreases from 19.54 nm to 12.59 nm, indicating that the increase of CaO/MgO molar ratio may change the glass network structure to affect the crystallization behaviours of quantum dots. Due to the different radius scale of Ca2+ and Mg2+, they have different energies when occupying the sites in glass matrix. When Mg2+ is replaced by Ca2+, there will be an energy difference, resulting in a decrease in the ability of providing free oxygen, so the BO in the glass increases, which strengthens the glass network. With the increase of the molar ratio of CaO/MgO, the layered structure gradually weakens, and the transition from the layered structure of [BO3] to the framework structure of [BO4] leads to the weakening of the layered characteristics and the dense structure of the glass network, resulting in an increase in the crystallization temperature and a decrease in the average size of the quantum dots. The obtained samples exhibit excellent optical properties. PL spectra of CsPbBr3 quantum dot glass samples with different CaO/MgO molar ratios were heat-treated at 480 ℃ for 10 h shows strongly varied luminescence intensity. The intensity becomes higher until the peak point with the increase of the molar ratio of CaO/MgO. When CaO replaces MgO in small amounts, the glass network expands because the ionic radius of Ca2+ is larger than that of Mg2+, and the influence of molecular weight and atomic radius on the glass matrix plays a dominant role, thereby promoting the migration of Cs+, Pb2+ and Br–, so that CsPbBr3 quantum dots are precipitated in the glass matrix and the luminescence is enhanced. When the molar ratio of CaO/MgO is 2:3 (CA2), the luminescence intensity reaches the maximum value. At this point, the internal quantum efficiency of the CsPbBr3 quantum dot glass sample is 45.2%, the external quantum efficiency is 36.0% under excitation of 455 nm, and the calculated absorption efficiency is 79.6%. After three times of heating-cooling (298?473 K) cycles, the luminous intensity of the optimal sample gradually returns to the initial value, and the peak emission wavelength and FWHM also show obvious temperature dependence and excellent recovery ability, indicating that the CsPbBr3 quantum dot glass has good luminescence thermal stability.
Conclusions CsPbBr3 perovskite quantum dots were successfully precipitated in borosilicate glass matrix by traditional melt quenching-heat treatment method. Under the same heat treatment conditions, when the molar ratio of CaO/MgO increases, the average size of quantum dots decreases, and the luminescence quantum efficiency increases first and then decreases. The bond breaking effect of Ca2+ and the mixed alkaline earth effect make the luminescence performance of the CsPbBr3 quantum dot glass sample the best when the molar ratio of CaO/MgO is 2:3, corresponding to an internal quantum efficiency of 45.2%, an external quantum efficiency of 36.0%, and an absorption efficiency of 79.6% under excitation at 455 nm. It also shows good luminescence thermal stability. At the same time, the CsPbBr3 quantum dot glass crystallization is uniform and exhibits high transmittance, which is promising to be applied in the field of optical filters.