Study On The Photoluminescence Characteristics Of LiYO₂:Eu³⁺ And KYO₂:Tb³⁺ Nanophosphors Applied To WLED

A white light diode（WLED）is a type of light source that has become popular in the sectors of lighting and display because of its excellent brightness,low power consumption,and less pollution.Therefore,the key challenge of current WLED research is how to improve luminous efficiency and characteristics,which has attracted the attention of academics and enterprises.In this thesis,the luminescence characteristics of self-made WLEDs have been discussed,as well as nanophosphors emitting red and green light,respectively.The concrete works are as follows:Firstly,LiY_1-xO₂:xEu³⁺and KY_1-yO₂:yTb³⁺nanophosphors have been synthesized by high-temperature solid-phase method.XRD results that the incorporation of Eu³⁺or Tb³⁺has little effect on the crystal structure of the matrix.The particles of two series of samples are spherical and distributed equally in SEM.The results indicate that the average particle size increases slightly when the rare earth ions Eu³⁺or Tb³⁺are doped.Secondly,the excitation and emission spectra of LiY_1-xO₂:xEu³⁺series phosphors have been measured and analyzed.When the monitoring wavelength is 617 nm,samples have emission peaks at 396 nm,468 nm,and 537 nm.And samples emit intense red light（617 nm）excited at 396 nm.The optimized concentration of Eu³⁺is 0.35 mol,which color purity can reach 93.6%.It means that the sample can be used in WLED production,compensating for the lack of red light in the current commercial WLED devices,so as to improve its correlated color temperature and tone.The optimized mixing ratio of LiY_0.65O₂:0.35Eu³⁺and Y₃Al₅O₁₂:Ce³⁺yellow phosphor has been explored,and then the mixed powder is coupled with LED（460-470nm）.The WLED with the correlated color temperature of 5308 K and the color rendering index of 90 has been made.Thirdly,the photoluminescence characteristics of KY_1-yO₂:yTb³⁺nanophosphors have been systematically discussed,and the results show that the addition of alkali（earth）metal ions improve the photoluminescence intensity up to 4-11 times.When excitation wavelength is 307nm,the central wavelengths of emission peaks are 489 and 547 nm corresponding to the transition of Tb³⁺ions ~5D₄→~7F₆,~7F₅,where optimal doping concentration is 0.015 mol.At the same time,coupling the optimized sample with 300-310 nm LED using an optical glue,which means that a self-made green LED has been obtained with a strong green light emission.Finally,the applications of the prepared red and green phosphors in WLED are introduced.The optimized excitation wavelength and mixing ratio of two series of phosphors have been discussed,i.e.,356 nm and 1:1.The warm white light-emitting phosphors with color coordinates（0.344,0.366）and the color rendering index of 87 have been achieved,which is used for WLEDs.The effects of driving voltage,frequency,duty cycle,and output waveform on the luminous performance of WLED devices are analyzed in detail.The results show that with the increase of voltage,the luminous intensity and the color rendering index are improved,but the color coordinates basically do not move and remain in the white light region.At the same time,the intensity of WLED basically does not fluctuate as the power frequency changes,indicating that the device is suitable for indoor（table lamp）lighting and will not cause visual fatigue.In addition,a power-saving brightness regulation mode based on the duty cycle is proposed,which further proves that the two series of phosphors can be used in the production of high-quality WLED and will play an important role in the fields of lighting and display.