Preparation And Performance Study Of SrLu₂O₄:Ce³⁺ Blue Phosphor Excited By Near Ultraviolet

With the advancement of white light-emitting diodes(w-LEDs)technology and human pursuit of higher lighting quality,the full-spectrum w-LEDs has attracted widespread attention in the industry due to their excellent performance,such as safety and health,high color reduction and saturation,and good spectral continuity.In recent years,SrLu2O4:Ce3+blue phosphor has been reported,its main excitation peak matches well with near ultraviolet LED chip,and full width at half maximum(FWHM)is wide,high thermal stability,which shows that SrLu2O4:Ce3+has a very good application prospect in full-spectrum w-LEDs.However,the current research on this phosphor is inadequate,the luminescence mechanism is still unclear.Especially,the preferential occupation position of the activator Ce3+ is unclear,and the spectrum is not adjusted,and the luminous efficiency is not improved.Therefore,this thesis carried out detailed research on these issues.SrLu2O4:Ce3+phosphor was synthesized at the different temperature by the high temperature solid-sate reaction method.The study found that SrLu2O4:Ce3+phosphors synthesized atl560℃ or 1600℃ have one more excitation band with peak at around 360 nm than that at 1480℃ or 1520℃.Meanwhile,with the increase of synthesis temperature,the photoluminescence emission(PL)intensity increases,the PL bands shows a slight red shift,and the emission of the shoulder peak region is enhanced.Combining the refinement of crystal structure,characterization of luminous properties,and theoretical analysis of crystal field,it is concluded that Ce3+of SrLu2O4:Ce3+synthesized at 1480℃ or 1520℃occupies only Sr2+sites,while Ce3+of SrLu2O4:Ce3+synthesized at 1560℃ or 1600℃occupies Sr2+and Lu3+sites.The photoluminescence of SrLu2O4:Ce3+phosphor was studied.Analysis found that the phosphor was efficiently excited in the 250-430 nm region,and could achieve emission in the region of 420-600 nm with a peak wavelength of 459 nm,and FWHM is about 90 nm.The emission intensity increases as the Ce3+ion concentration increases,up to 0.15%,then tends to decrease gradually due to the concentration quenching effect,the major quenching mechanism on the doping levels is dipole-dipole interaction.The external quantum efficiency of SrLu2O4:Ce3+at 150℃(423 K)remian 84.3%of that of the room temperature(298 K),which showed that its temperature characteristic is obviously superior to the current commercial blue phosphor.By replacing Sr2+ by Ca2+,the crystal structure and photoluminescence properties of Sr1-xCaxLu2O4:Ce3+(x=0-1.0)phosphors were studied.With increasing x,the crystal field splitting and Stokes shift of Sr1-xCaxLu2O4:Ce3+were increase,which results that the excitation peak of Sr1-xCaXLu2O4:Ce3+phosphors were red-shifted from 405 to 420 um,and the dominant emission peak could be red-shifted from 459 to 503 nm.The performance of Sr1-xCaxLu2O4:Ce3+(x=0-0.2)phosphors was investigated in detail.The emission peaks of the Sr1-xCaxLu2O4:Ce3+(x＝0-0.2)phosphors can be red-shifted from 459 to 465 nm.When x=0.2,the emission intensity is increased by 23%,the external quantum efficiency is increased by 34.9%.And since the thermal quenching activation energy and band gap width were increase,the thermal stability of Sr1-xCaxLu2O4:Ce3+was further improved by the substitution of Ca2+ions(86.2%).The application performance of Sr1-xCaxLu2O4:Ce3+(x=0-0.2)was evaluated.W-LEDs was fabricated by using Sr1-xCaxLu2O4:Ce3+(blue),,β-sialon:Eu2+(green)and(Sr,Ca)AlSiN3:Eu2+(red)phosphors combined a 405 nm near-UV LED chip.When applying Sr0.8Ca0.2Lu2O4:Ce3+or SrLu2O4:Ce3+as the blue phosphor,the former package device had the higher luminous efficiency than the latter one,and CRI of both devices greater than 95.0.These results show that Sr1-xCaxLu2O4:Ce3+was a potential blue phosphor for n-UV pumped full-spectrum w-LEDs application.