Investigation On Design,Fabrication And Properties Of New Polyoxide-based Luminescent Materials For Pc-LEDs

With the significant improvement of the photoelectric efficiency of blue and near-ultraviolet LEDs,pc-LEDs have been broadly applied in lighting,display and special light sources due to its advantages of energy saving,efficiency,compactness and durability.As an important component of pc-LEDs,the performance of phosphor determines the quality and application prospects of pc-LEDs.Therefore,exploring new phosphors with excellent performance and adjustable emitting color has become a research focus.In this paper,we conducted research from three directions:crystal structure,local environment and activator ion.Through the strategies of co-substitution of structural units,heterovalent substitution of alkali metal sites,energy bridges and mixed valence state,etc,a variety of phosphors with adjustable properties have been designed and prepared.The crystal structure,luminescence mechanism and practical applications in various fields have been systematically studied.The main research contents are as follows:（1）Efficient ultra-narrow-band green/yellow phosphors Na₃Tb（PO₄）₂:Ce³⁺/Eu²⁺were designed and synthesized.Benefiting from the sensitization of Ce³⁺and Eu²⁺,the quantum efficiency of Na₃Tb（PO₄）₂:Ce³⁺is up to 94.5%,and Na₃Tb（PO₄）₂:Eu²⁺presents bright yellow-emitting with a colour purity of 73%.The thermal stability of Na₃Tb（PO₄）₂:Eu²⁺was effectively improved by the construction of Na⁺vacancies.The application potential of Na₃Tb（PO₄）₂:0.15Ce³⁺and Na_2.95Tb（PO₄）₂:0.03Eu²⁺in pc-WLED has been evaluated.The results show that the device made of Na_2.95Tb（PO₄）₂:0.03Eu²⁺has higher color rendering index（Ra=83.5）and lower color temperature（CCT=5206 K）.（2）A new deep-red phosphor Li₆CaLa₂Nb₂O₁₂:Mn⁴⁺with garnet structure was designed and synthesized.The ultra-wide PLE spectrum enhances its LED adaptability.Based on the high efficiency of energy transfer between Bi³⁺and Mn⁴⁺,Bi³⁺was used as sensitizer to further optimize the luminescent property.A full-spectrum pc-WLED with low CCT（4553 K）,high Ra（96.4）and ideal CIE coordinates（0.336,0.356）was prepared using Li₆CaLa₂Nb₂O₁₂:0.004Mn⁴⁺,0.01Bi³⁺.（3）A new ultra-broadband green phosphor K₃La（PO₄）₂:Eu²⁺without cyan gap was designed and synthesized.Three objectives,namely,quantum efficiency improvement（25.97%→55.25%）,thermal stability enhancement（55.1%@150℃→80.2%@150℃）and tunable luminous color（green→cyan→blue）,have been achieved in K₃La（Ca/Sr/Ba）（PO₄）₂:Eu²⁺by using the double-heterovalent substitution strategy.Based on K₃La_0.9Ca_0.1（PO₄）₂:Eu²⁺,a high-quality full-spectrum pc-WLED（Ra=96,CCT=4853 K）pumped by a UV chip was prepared by dichromatic approach.This study provides an effective regulatory strategy for the development of ultra-broadband phosphor.（4）A series of new multi-color phosphors Sr₃Sc₄O₉:xEu were designed and synthesized.With increasing doping concentration,Eu²⁺selectively occupies multiple cationic sites（Sr1-3 and Sc1-4）in Sr₃Sc₄O₉ matrix,thus achieving the tuning of the luminous color from deep-red to white to green.Under blue light excitation,Sr₃Sc₄O₉:0.006Eu shows an asymmetric deep-red emission band,peaking at 688nm.The emission band is well matched with the absorption curves of phytochrome(P_r and P_fr).Using the double-reduction processing,the emission intensity of the deep-red light can be improved by about 20 times.Under UV excitation,Sr₃Sc₄O₉:0.01Eu exhibits full-spectrum white light emission.The pc-WLED prepared by Sr₃Sc₄O₉:0.01Eu and 365 nm UV chip showed excellent electroluminescence（CCT=5040 K,Ra=86）.The above results indicate the application potential of Sr₃Sc₄O₉:xEu in indoor planting and full spectrum lighting.This study provides a new method for the development of single-component white phosphor.（5）Eu^2+/3+doped Sr_1.95+xLi_1-xSi_1-xAl_xO₄F（0≤x≤0.25）phosphors were prepared by crystal field regulation strategy in a reducing atmosphere.The correlation between the local crystal structure and the luminescent properties is expounded in detail.Based on the different temperature sensitivity of Eu²⁺and Eu³⁺,a temperature sensor with color discrimination is designed,its maximum absolute and relative sensitivity are 0.0294 K^-1 and 0.83%K^-1,respectively.Based on the excitation wavelength dependence of luminous color,fluorescent anti-counterfeit paper and anti-counterfeit pattern are designed and manufactured.The hidden color or image is displayed in the form of green/orange-red light under the excitation of365/300 nm light.In addition,Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu shows excellent stability in both humid and acid-base environments.All the above conclusions indicate that Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu has application potential in the field of multi-color anti-counterfeiting and optical temperature measurement.