Cesium Lead Bromide-Doped Potassium Bromide Crystal and Its Growth Method

Abstract

The potassium bromide crystal doped with cesium lead bromide and its growth method belong to the technical field of luminescent materials. The existing CsPbBr3 perovskite material has poor environmental stability. The potassium bromide crystal doped with cesium lead bromide in the present invention uses CsPbBr3 as the luminescence center. The potassium bromide crystal doped with cesium lead bromide belongs to the cubic crystal system, and its molecular formula is KBr:CsPbBr3. CsPbBr3 is the dopant and the crystal matrix is KBr. The growth method of the potassium bromide crystal doped with cesium lead bromide in the present invention comprises the steps of growth material preparation, crystal growth and annealing. In the growth material preparation step, CsBr and PbBr2 are added according to a molar ratio of CsBr:PbBr2 = 1.2 - 1.8:1, and the addition amount of KBr is determined according to the molar concentration of CsPbBr3 in KBr:CsPbBr3 being greater than 0.5 at.% and less than 45 at.%. In the crystal growth step, the KBr:CsPbBr3 crystal is grown by the Czochralski method, and the process parameters are determined as follows: the pulling speed is 0.8 - 1.5 mm / h, the rotation speed is 2 - 15 rpm, and the growth temperature is 721 - 728 °C. In the annealing step, the pulling is stopped, and it is kept warm at the growth temperature for 25 - 35 min, then naturally cooled to 650 °C and kept warm for 5 - 6 h, and then naturally cooled to room temperature.

Description

Technical Field

[0001] The present invention relates to a technical solution titled "Potassium Bromide Crystal Doped with Cesium Lead Bromide and Its Growth Method". In the present invention, potassium bromide is combined with cesium lead bromide perovskite crystal to form an optical crystal with the molecular formula KBr:CsPbBr3, belonging to the technical field of luminescent materials. Background Art

[0002] Due to its "113 structure", CsPbBr3 belongs to perovskite materials, having a high photoluminescence quantum yield (PLQY), a narrow emission spectrum, and being tunable, covering the entire visible range. This makes CsPbBr3 perovskite materials have unique applications in the field of luminescent materials. Compared with polycrystalline thin films, single-crystal perovskite without grain boundaries has a faster light response speed and higher monochromaticity. Therefore, the fabrication of CsPbBr3 single-crystal perovskite is a prerequisite for further exploring the potential of single-crystal perovskite in various applications. Due to the poor environmental stability of CsPbBr3, it is extremely easy to undergo a phase change in an environment of light, high temperature, and humidity, and thus needs to be encapsulated for use. Summary of the Invention

[0003] In order to grow CsPbBr3 crystals with high environmental stability and thus not easily undergo a phase change due to environmental factors, we propose an invention called "Potassium Bromide Crystal Doped with Cesium Lead Bromide and Its Growth Method".

[0004] The potassium bromide crystal doped with cesium lead bromide of the present invention has CsPbBr3 as the luminescence center. It is characterized in that the potassium bromide crystal doped with cesium lead bromide belongs to the cubic crystal system, with the molecular formula KBr:CsPbBr3, CsPbBr3 being the dopant, and the crystal matrix being KBr.

[0005] The growth method of the potassium bromide crystal doped with cesium lead bromide of the present invention includes steps of growth material preparation, crystal growth, and annealing. It is characterized in that, in the growth material preparation step, CsBr and PbBr2 are added according to a molar ratio of CsBr:PbBr2 = 1.2 - 1.8:1, and the addition amount of KBr is determined according to the molar concentration of CsPbBr3 in KBr:CsPbBr3 being greater than 0.5 at.% and less than 45 at.%; in the crystal growth step, the Czochralski method is used to grow the KBr:CsPbBr3 crystal, and the process parameters are determined as: the pulling speed is 0.8 - 1.5 mm / h, the rotation speed is 2 - 15 rpm, and the growth temperature is 721 - 728 °C; in the annealing step, the pulling is stopped, and the in-situ annealing method in the furnace is adopted, keeping warm at the growth temperature for 25 - 35 min, then naturally cooling to 650 °C and keeping warm for 5 - 6 h, and then naturally cooling to room temperature.

[0006] The technical effect of the present invention is that potassium bromide is combined with cesium lead bromide perovskite crystal to form potassium bromide crystal doped with cesium lead bromide, which is an optical crystal. The combination does not change the crystal system structure of the product crystal, and it still has the cubic crystal system structure of potassium bromide, as Figure 1 described. The diffraction peak positions of the KBr:CsPbBr3 crystal and the KBr lattice in the figure match. The potassium bromide crystal has good environmental stability, which brings the same environmental stability to the KBr:CsPbBr3 crystal. During the test of the product crystal sample, after two temperature rises and falls above the phase transition point temperature of CsPbBr3, which is 243 °C, and then the spectral test is carried out on the product crystal sample, it can still maintain more than 99% of the initial light intensity; the light intensity does not change significantly under humid and light conditions, and the environmental stability is better than that of pure phase CsPbBr3.

[0007] The technical effect of the present invention is not limited to this.

[0008] For example, since the lattice matching degree between the (-211) plane of KBr and the (220) plane of CsPbBr3 is as high as 98.94%, the doping concentration range is relatively wide. The molar concentration of CsPbBr3 in KBr:CsPbBr3 is between 0.5 at.% and 45 at.%. Within this range, it can not only ensure the normal luminescence of the product crystal, but also ensure that KBr:CsPbBr3 has the same crystal system structure as KBr, so as to meet various actual needs. For example, when the molar concentration of CsPbBr3 in the KBr:CsPbBr3 crystal is 5.3 at.%, the peak value of the luminescence light intensity of the product crystal is even higher than that of CsPbBr3, as Figure 2 shown.

[0009] Again, CsBr is added in excess according to CsBr:PbBr2 = 1.2 - 1.8:1. The extra Cs can fill other defects in the product crystal; at the same time, by using the phenomenon of melting point reduction of the mixture, the growth temperature is determined in the range of 721 - 728 °C, which is lower than and close to the melting point of KBr, 730 °C. While ensuring the normal growth of the crystal, it reduces the volatilization of the melt components, especially reducing the volatilization of PbBr2 and CsBr, which originally had a heavier volatilization, while the volatilization of KBr, which originally had a lighter volatilization, is further reduced in the range of 721 - 728 °C. The combined effect of the two technical measures is that it is easy to grow relatively perfect crystals, including obtaining large-size product crystals with dimensions such as Φ10mm×35mm in terms of size, and achieving uniform doping in terms of doping.

[0010] Furthermore, the grown potassium bromide crystal doped with cesium lead bromide not only has a spectrum similar to that of CsPbBr3, as Figure 2 shown, but also is easy to process and can be used to manufacture light-emitting devices such as light-emitting diodes. Description of the Drawings

[0011] Figure 1 The XRD diagram of the potassium bromide crystal doped with cesium lead bromide of the present invention compared with potassium bromide crystal, which also serves as an abstract figure.

[0012] Figure 2 The luminescence spectrum diagram of the potassium bromide crystal doped with cesium lead bromide of the present invention is compared with that of the lead cesium bromide crystal. DETAILED DESCRIPTION

[0013] The method for growing potassium bromide crystals doped with cesium lead bromide of the present invention comprises the steps of preparing a growing material, growing a crystal and annealing. In the growing material preparation step, CsBr and PbBr2 are added at a molar ratio of CsBr:PbBr2=1.2-1.8:1, such as CsBr:PbBr2=1.72:1, and the amount of KBr added is determined according to the molar concentration of CsPbBr3 in KBr:CsPbBr3 being greater than 0.5at.% and less than 45at.%, such as the molar concentration of CsPbBr3 in KBr:CsPbBr3 being 5.3at.%, KBr and CsBr are mixed first, and then PbBr2 is added and fully mixed, and a block is obtained by pressing with a hydraulic press to obtain a block growing material. In the crystal growth step, the prepared growth material is loaded into a single crystal furnace, and a KBr:CsPbBr3 crystal is grown by a pulling method, and the process parameters are determined as follows: a pulling speed of 0.8-1.5 mm / h, a rotation speed of 2-15 rpm, and a growth temperature of 721-728° C., such as a pulling speed of 1.2 mm / h, a rotation speed of 10 rpm, and a growth temperature of 723° C. In the annealing step, the pulling is stopped, and an in-situ furnace annealing method is adopted, and the temperature is kept at the growth temperature for 25-35 minutes, such as 30 minutes, and then the temperature is naturally reduced to 650° C. and kept for 5-6 hours, such as 6 hours, and then the temperature is naturally reduced to room temperature.

[0014] Theoretically, CsBr:PbBr2=1:1. In order to add more Cs to fill other defects in the product crystal, the ratio of CsBr:PbBr2=1.72:1 is determined. However, according to experience, the total amount of CsBr and PbBr2 also needs to be increased to make up for the loss of growth materials caused by the volatilization of these two components. For example, the total amount of growth material is determined to be 1.5 mol, of which KBr is 1.42 mol, and then CsBr is determined to be 0.138 mol and PbBr2 is 0.08 mol. The amount of both added is consistent with the ratio of CsBr:PbBr2=1.72:1, but the remaining amount of the growth material component after the KBr is determined to be 1.42 mol is to make up for the loss of growth materials caused by the volatilization of these two components.

Claims

1. A method for growing a potassium bromide crystal doped with cesium lead bromide, the steps of which include growth material preparation, crystal growth, and annealing, characterized in that, In the growth material preparation step, CsBr and PbBr2 are added at a molar ratio of CsBr:PbBr2 = 1.2 - 1.8:1, and the addition amount of KBr is determined according to the molar concentration of CsPbBr3 in KBr:CsPbBr3 being greater than 0.5 at.% and less than 45 at.%; in the crystal growth step, the KBr:CsPbBr3 crystal is grown by the Czochralski method, and the process parameters are determined as follows: the pulling speed is 0.8 - 1.5 mm / h, the rotation speed is 2 - 15 rpm, and the growth temperature is 721 - 728 °C; in the annealing step, the pulling is stopped, and the in-situ furnace annealing method is adopted. It is kept at the growth temperature for 25 - 35 min, then naturally cooled to 650 °C and kept for 5 - 6 h, and then naturally cooled to room temperature.

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