ABSTRACT
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.
ABSTRACT
The collagen I was made with the dialysis method of enzymolysising the pig skin, and the static deposition in vitro of calcium phosphate was comparative studied by X-ray diffraction (XRD) and infrared spectroscopy (FTIR) under the condition of pH7. 4, Ca/P 1.67 and whether adding the collagen I into the system. Then the chemical composition of the sedimentary product and the diversification of the collagen I 's IR and Raman spectra (RS) before and after the mineralization were analyzed. The results showed that,under the physiological pH condition that there was not any collagen I, though Ca/P reached up to 1.67, the sedimentary product was CaHPO4 x 2H2O yet, however, after adding collagen I into the system, the bone-like apatite was deposited, which proved that collagen I indeed had the effects on the inducing of the bone-like apatite's mineralization in vitro; there was obviously mutual coordination action between collagen I and its mineralization product--bone-like apatite, which caused that amide peak I red-shifted, amide peak II and amide peak III decreased significantly or disappeared on the IR of collagen I, which maybe was the mechanism that how collagen I induced the depositing of the bone-like apatite.
