Site Engineering,spectral Regulation And Device Application Of The Phosphors Based On β-Ca₃PO₄ Structure

The advancement of display and lighting technology has significantly enriched and improved people’s daily lives.However,there are limitations in the current research on fluorescent powders,which typically focuses on case studies rather than a universal method model.To address this issue,we have developed a set of universal spectral tuning methods based on the Ca₉Nd（PO₄）₇matrix and tested their feasibility.We explored single-and dual-doping models in the matrix material,co-doping of metal luminescent ions,and regulation of the environment of rare earth doped lattice sites to achieve better color rendering.These methods were then successfully extended to theβ-Ca₃（PO₄）₂material system,resulting in the development of a single-component white fluorescent powder through the coupling of multiple tuning methods.Our findings verify the universality and feasibility of the matrix structure-spectral tuning research program,which holds great promise for future research in this field.Detailed contents are listed below:（i）To gain insight into the site preference of rare-earth dopants in CNP hosts,Ce³⁺and Tm³⁺&Tb³⁺pair with similar ionic radii to the Ca ions were selected first as probe ion（s）.XRD refinements and theoretical simulation both confirmed that the rare-earth dopants mainly took the Ca1,Ca2,and Ca3 sites,while the Ca4 site with low coordination number and high local symmetry was absent in the doping process.The variation in charge density after doping rare-earth ions was revealed by theoretical simulations.The variations can be viewed as only localized difference in bond angle and charge distribution,yet such minor distortion can be integrated into a bigger one,leading to unstable structures,which is why impurities emerge at high doping concentrations.The electronic structure of CNP was simulated as an in-direct semiconductor with a large band gap of～4 e V,which is enough for taking into new impurity levels from dopants.Based on the research,we have gained insight into the dopant distribution of CNP in different situation,and the fact that CNP has a large space for doping concentration of different luminescent ions,as well as a weak interaction between the dopants to realize multi-peak emission.（ii）Based on the thorough study on the doping behavior in CNP,we then proceeded to design and synthesize a red phosphor CNP:Eu³⁺with high thermal stability.In order to solve the weak excitation in the blue region,a Sm³⁺co-doping strategy was further used with the premier multi-center doping model for CNP.The CNP:Eu³⁺has initially possessed high thermal stability that it can remain 84.3%of the pristine luminescence intensity at 373 K,and 70.4%at 423 K.Compared to CNP:Eu³⁺,the Sm³⁺signal emerged in the CNP:Eu³⁺,Sm³⁺sample together with the Sm→Eu energy transfer to enhance the blue light excitation.In addition,the CNP:Eu³⁺,Sm³⁺has shown more intense luminescence and larger R_ccompared to the single doped ones,which copes well with the previously model probed by Tm&Tb.（iii）We then continued on the site engineering and modification based on CNP using Sr/Ca substitution and Eu²⁺activator.Both XRD refinement and DFT simulation indicate the Sr-Ca3 preferable substitution,which enlarge the difference in environments of the Ca sites in CAP.The single Eu-doped CNP shows a wide PL peak ranging from green region to the infrared region,which is undesirable as red phosphor in WLED.The Sr-guided Sr-Ca3 and then Eu-Sr site engineering greatly modified the Eu site occupation,leading to restricted Eu luminescence.The focused luminescence intensity on the red region instead of the unwanted yellow,green and infrared make CNP:Sr²⁺,Eu²⁺a promising phosphor for WLED.（iv）By integrating the above experiences,we integrated the spectral regulation methods onto CSPO with similar structure of CNP to realize single-component white light emittingβ-Ca₃（PO₄）₂:Sr²⁺,Mn²⁺,Eu²⁺.The experimental facts suggest that many properties of CNP can also be found in the CSPO,such as the dual-peak emission of both sensitizer and activator,the high doping capability,the large interaction distance,the thermal stability,and the Sr/Ca site engineering.We use XRD refinements and DFT simulation to investigate the site occupation thoroughly,where a similar Sr-Ca3,Eu-Ca3 and Mn-Ca5 substitution was found.By further adjusting the intensity ratio of the Mn/Eu dual-peak emission,we finally achieve a single-component warm white light emission.The WLED device fabricated withβ-Ca₃（PO₄）₂:Sr²⁺,Mn²⁺,Eu²⁺shows good stability to avoid performance degradation upon working for 20 h continuously,which indicates a superb application prospective.