Design of Eu3+-Doped Fluoride Phosphor with Zero Thermal Quenching Property Based on Density Functional Theory.

Although being applied in various fields, white light emitting diodes (WLEDs) still have drawbacks that urgently need to be conquered: the luminescent intensity of commercial phosphors sharply decreases at working temperature. In this study, we calculated the forming energy of defects and confirmed that the VNa defect state can stably exist in ß-NaGdF4, by density functional theory (DFT) calculation. Furthermore, we predicted that the VNa vacancies would provide a zero thermal quenching (ZTQ) property for the ß-NaGdF4-based red-light phosphor. Then, a series of ß-NaGdF4:xEu3+ and ß-NaGdF4:0.25Eu3+,yYb3+ red-light phosphors were synthesized by the hydrothermal method. We found that ß-NaGdF4:0.25Eu3+ and ß-NaGdF4:0.25Eu3+,0.005Yb3+ phosphors possess ZTQ properties at a temperature range between 303-483 K and 303-523 K, respectively. The thermoluminescence (TL) spectra were employed to calculate the depth and density of the VNa vacancies in ß-NaGdF4:0.25Eu3+ and ß-NaGdF4:0.25Eu3+,0.005Yb3+. Combining the DFT calculation with characterization results of TL spectra, it is concluded that electrons stored in VNa vacancies are excited to the exited state of Eu3+ to compensate for the loss of Eu3+ luminescent intensity. This will lead to an increase of luminescent intensity at high temperatures and facilitate the samples to improve ZTQ properties. WLEDs were obtained with CRI = 83.0, 81.6 and CCT = 5393, 5149 K, respectively, when phosphors of ß-NaGdF4:0.25Eu3+ and ß-NaGdF4:0.25Eu3+,0.005Yb3+ were utilized as the red-light source. These results indicate that these two phosphors may become reliable red-light sources with high antithermal quenching properties for WLEDs.

Preparation of a Transient Thermal Expansion Rock Cracking Agent by Deposition Method and Its Nonisothermal Kinetics Study with Isoconversional Procedure and DAEM.

Cracking agents are indispensable and important products for national energy exploitation and large-scale infrastructure construction. Transient thermal expansion rock cracking agent is a new cracking agent product with excellent performance that has just appeared in recent years. However, it is still prepared by mechanical ball milling, which is considered not the best choice among traditional methods for preparing energetic materials. In this paper, a transient thermal expansion rock splitting agent was prepared by the chemical deposition method using carbon black and calcium peroxide as raw materials. The TG/DTG results show that the mass loss of the sample can be divided into four stages with the increase of temperature. It is worth noting that the mass loss of the TG curve of the sample during the entire thermal decomposition process is 93.385%, and the instantaneous weight loss is 78.07% (ß = 15 °C/min). Kinetic analysis of the thermal decomposition process of the samples was performed using an isotransformation program and a distributed activation energy model (DAEM). The activation energy E α of the thermal decomposition of the sample was iteratively calculated. The results show that the a-E a curve of the sample can be divided into two stages. The pyrolysis kinetics of the first stage was successfully analyzed by the DAEM method and its thermal conversion behavior was predicted. The thermal decomposition behavior of the second stage was analyzed by a traditional kinetic analysis method.

A crystal defect led zero thermal quenching ß-NaYF4 : Eu3+,Dy3+ red emitting phosphor.

Red-light phosphors with extraordinary and stable thermal luminous properties must urgently be explored under the circumstances that commercial phosphors are suffering from serious thermal quenching effects and a lack of red-light components. Synthesized by a one-step hydrothermal method, a new type of NaYF4 : 0.065Eu3+,0.003Dy3+ phosphor with notable thermal luminous stability is reported in this study. As well as energy transfer between Dy3+ and Eu3+, this novel red-light phosphor manifests zero thermal quenching (ZTQ) performance under an increasing temperature of measurement. The ZTQ property stems from the interior defects of the crystal produced by the non-equivalence replacement between distinct ions. Density Functional Theory (DFT) calculations were utilized to verify the formation energy of two kinds of defects that make a vital contribution to the ZTQ performance of the NaYF4 : 0.065Eu3+,0.003Dy3+ phosphor. This finding could make some contributions towards research into improving thermal luminous properties and stability.

Synthesis and optical properties of Gd4Al2O9:Eu3+, a red emitting phosphor with a strong negative thermal quenching effect.

For the purpose of obtaining red-light phosphors with excellent luminescence thermal stability, a series of Gd4Al2O9:Eu3+ (GAO:Eu3+) phosphors were synthesized by combining the sol-gel method with high-temperature calcination, and a detailed series of study and analysis of their room temperature and high temperature luminescence properties was carried out. In GAO, the emission peaks corresponding to the 5D0 → 7F j (j = 0, 1, 2, 3 and 4) transitions of Eu3+ were observed at 578, 590, 610, 654, and 707 nm, with the strongest emission peak at 610 nm, and the obtained samples were red-light phosphors. The sample GAO:Eu3+ synthesized by combining the sol-gel method with high-temperature calcination has a negative thermal quenching (NTQ) effect, and the best doped sample GAO:0.16Eu3+ has an optimal luminescence temperature of 120 °C, and the corresponding integrated PL intensity is 183.2% of the initial value at 30 °C. The presence of the NTQ effect makes GAO:0.16Eu3+ have good luminescence thermal stability, which manifests as thermal-optical energy conversion at the macroscopic level. A detailed study of the thermal quenching mechanism was carried out.

Crystal defect induced zero thermal quenching ß-NaYF4: Eu3+, Sm3+ red-emitting phosphor.

Red phosphors with brilliant performance are crucial for the application of white LEDs as their red-light component. However, the thermal quenching phenomenon is an inevitable obstacle in the practical application of various types of red-light phosphors. In this study, we report the preparation of a novel type of phosphor, NaYF4: 0.065Eu3+, 0.002Sm3+, possessing not only an energy transfer effect from Sm3+ to Eu3+ but also superior negative thermal quenching (NTQ) performance. The phosphor was synthesized via a one-step hydrothermal method, resulting in a prominent improvement in its luminous thermal stability supported by NTQ. The NTQ originated from the thermal stimulation excitement of the captured electrons in electronic traps, which is attributed to the non-equivalence between the different types of ions. The shape of the emission spectrum measured at high temperature was identical to that measured at room temperature, which not only showed the remarkable thermal stability of this novel type of phosphor but also the promising prospect of its practical application. This finding will contribute to improving the thermal stability of phosphor materials doped with lanthanide elements.