The Optical Properties Of Ce³⁺:YVO₄Crystals And Its Application In White LED

YVO4crystal is an excellent birefringence and ferroelectric crystal. The structureis tetragonal and the space group isD194h(I41/amd). The cell parameters are a=b=0.71192nm, and c=0.62898nm. It has a wide transparency range, easy to growth andexcellent performance. Currently, it has become an excellent non-linear optical crystaland laser host crystal.Ce3+is an important rare earth ion. Because its energy level is relatively simple,and it has a wide absorption band, emission band, and high quantum efficiency of thelight emitting process. Thus, it can be used as a light emitting activator, and it can alsobe us ed as a s ensitizer. It ha s ve ry i mportant a pplications i n t he r are-earth-dopedphosphors. Another, the content of Ce3+on earth is rich, inexpensive, and easy to getfrom the mineral.Eu3+is another important rare earth. Its intrinsic emission in the red area is typicalof the line spectra. Eu3+ions are used extensively for early color television sets andother display devices. Currently, Eu3+has become the mainstream development of thered phosphor. It can be the activator of red phosphor directly, and it can also improvethe display index of the luminescent materials.The white LED has many advantages, such as high energy efficiency, low energyconsumption, pol lution-free, l ong life t ime, s afety and so on. At the moment, itbecomes more and more important in the scientific and technological research. It hasbecome the subject of modern solid-state lighting and it will become the future trendof the times, unstoppable. Therefore, the development of highly efficient white LEDhas become a research focus of the solid-state lighting.First of all, a series of high-quality Ce3+:YVO4, Ce3+/Eu3+:YVO4crystals and othercrystals were grown. The growth process has been studied, and the growth processand the crystal quality is improved. The efficiency of the crystal growth is furtherimproved. In addition, the high quality of Ce3+/Eu3+:YVO4crystal has been grown forthe first time.Second, in the spectral characteristics of a s eries of Ce3+:YVO4crystals has beenresearched. The light-emitting characteristics and the luminescence mechanism arestudied when the Ce3+:YVO4crystals are excitated under different wavelengths. Therelationships between the ene rgy l evels with the a bsorption s pectrum, e xcitationspectrum and emission spectrum have been studied. The valence of the cerium ion and the oxygen ion in YVO4crystal h as beenstudied. It has been found that the Ce3+ion and the Ce4+ion always coexist together.The “Ce-O” charge transfer state (CTS) has been formed, due to the coexistence ofCe3+and Ce4+, which reveals the mechanism of unusual luminescence properties ofCe3+:YVO4crystal. The "molecular orbital theory" is used to explan this phenomena.An unusual upconversion luminescence in the Ce3+:YVO4crystal has been found.We have found that this special luminescence is also due to the charge transfer state of“Ce-O”.Eu3+ions have been doped into the Ce3+:YVO4crystal, in order to improve thelight-emitting characteristics of the materials. The spectral characteristics of Ce3+/Eu3+: YVO4crystal have been studied, and the energy levels of Ce3+and Eu3+andenergy t ransfer ha s be en discussed. Compared t o t he C e3+:YVO4crystal, theluminescence of Ce3+/Eu3+:YVO4crystal is unique.It i s found t hat C e3+:YVO4crystals m ay b ecome a n ew ki nd of efficientultraviolet blue phosphors from the spectrum of the Ce3+:YVO4crystals. The bluelight has been seen by naked eyes when the Ce3+:YVO4crystals is excited by the laserirradiation.The Spectrum of the Ce3+/Eu3+:YVO4crystals show that it radiate red light underultraviolet l ight, w hich can b e s een b y n aked eyes. It w ill be a ne w type of redphosphors. In addition, under the excitation of near ultraviolet light (397nm), CIEcoordinates are cal culated from t he em ission spectrum. We ha ve f ound t hat t hecoordinates are exactly in white light light-emitting area. That is to say that, it willhopefully become a phosphor which can emit white light by a single phosphor.The l uminescent cha racteristics of t he C e3+:YVO4crystal and Ce3+/Eu3+:YVO4crystals in the application of white LED are discussed.