Fabrication And Properties Of Bimodal LuAG Fluorescent Ceramics For High Chromogenic Laser Lighting

Laser lighting is an emerging lighting technology that composed of laser and fluorescent materials.Because of its advantages of high light efficiency,strong directionality,good monochromatic property and suitable for optical fiber transmission,it can also solve the problem of sudden drop in high power LED efficiency.It has attracted wide attention from many scientific researchers,and it is expected to be widely used in aircraft headlights,backlights,projectors,and seabed exploration.Fluorescent ceramics have the advantages of high thermal conductivity,high transmittance,high luminous efficiency,corrosion resistance,high temperature resistance,long life and easy doping.The fluorescent material plays the role of light conversion in laser illumination,which is a very key factor to realize white light illumination.Since the output energy of laser lighting is much higher than that of LED lighting,the fluorescent material used for laser lighting needs to withstand a certain thermal load while converting light.Fluorescent ceramics have the advantages of high thermal conductivity,high light transmittance,high luminous efficiency,corrosion resistance,high temperature resistance,long life,and easy doping.It is a very suitable fluorescent material for laser lighting.However,the current transmittance of Lu AG fluorescent ceramics is low,and the lack of red light components in Lu AG:Ce³⁺fluorescent ceramics causes the assembled laser lighting system to have problems of low color rendering index and high color temperature,which cannot meet modern lighting quality requirements.In order to solve the above problems,this paper conduct ceramic sintering in vacuum tungsten furnace by high temperature solid phase method.The main research contents are as follows:（1）Preparation and performance study of Lu AG transparent ceramics and Lu AG:Ce³⁺fluorescent transparent ceramics.The transparent ceramics were sintered in a vacuum tungsten furnace at 1700℃by high temperature solid phase method.Through the method of controlling a single variable,the influence of the doping amount of the cosolvent silica,the milling time of the raw material,and the ceramic sintering process on the transmittance of the ceramic sheet were explored.Then,the Lu AG matrix was doped with different contents of Ce³⁺to prepare fluorescent ceramics.By X-ray diffraction（XRD）,scanning electron microscope（SEM）,fluorescence spectrophotometer,ultraviolet visible spectrophotometer UV-Vis)characterization methods,the phase structure of the ceramic was tested,and the transparent ceramics under different experimental conditions were analyzed.Grain boundary structure and grain size,the excitation spectrum and emission spectrum of fluorescent ceramics,as well as the ceramic transmittance under different experimental conditions were tested.The results show that when the Si O₂doping amount is 0.2 wt%,Ce³⁺concentration is x=0.02,the Lu AG:Ce³⁺ceramics have a high transmittance of 76%at 800 nm.Meanwhile,the emission spectral redshift of22nm.（2）Research on occupancy of Mn²⁺ions in Lu AG:Ce³⁺ceramics and luminescence performance:In order to improve the color rendering of laser illumination,the emission spectrum of fluorescent materials needs to have a red spectrum part.However,Lu AG:Ce³⁺fluorescent ceramics lack red light.We doped Lu AG:Ce³⁺ceramics with different concentrations of Mn²⁺ions to increase the red light component to improve the color rendering of laser illumination.The ceramics were characterized by XRD,SEM,EDS spectrometer,fluorescence spectrophotometer,and ultraviolet-visible spectrometer,and the energy transfer efficiency of Ce³⁺ions to Mn²⁺ions with different contents was calculated.The results show that when Mn²⁺ions enter the Lu AG matrix,they first occupy the octahedral position of Al³⁺ions.After the concentration is too high,excessive Mn²⁺ions occupy the dodecahedral position of Lu³⁺ions.The doping of Mn²⁺ions increased the red light component in the emission spectrum.With the increase of the concentration of Mn²⁺ions,a series of fluorescent transparent ceramics from green to yellow to orange-red were successfully prepared,and the energy transfer efficiency gradually increased.（3）The effect of Gd³⁺ions on the luminescence performance and transmittance of Lu AG:Ce³⁺,Mn²⁺ceramics:Due to the luminescence characteristics of Mn²⁺in the Lu AG matrix,it emits orange-red light at 588 nm,resulting in a smaller proportion of red light in the emission spectrum of Lu AG:Ce³⁺and Mn²⁺ceramics,and when the doping Mn²⁺concentration is high,the transmittance decreases more.We successfully prepared Lu_3-xGd_xAl₅O₁₂:Ce³⁺,Mn²⁺fluorescent transparent ceramics by replacing part of Lu³⁺with Gd³⁺.The ceramics were characterized by XRD,SEM,EDS spectrometer,fluorescence spectrophotometer,and ultraviolet-visible spectrometer.The results show that the doping of Gd³⁺ions makes the emission peak of Ce³⁺ions red-shifted by 30 nm,and the emission peak of Mn²⁺ions is red-shifted by 20 nm.Increasing the proportion of red light,and the color rendering property is increased from 80.1 to 81.5,and the transmittance of the ceramic is improved under the same Mn²⁺concentration.（4）The construction and application performance of the laser lighting system:The clamping device with adjustable distance between the laser diode and the ceramic sheet was designed,and the laser lighting system was built.Through the HSP6000spectrum analysis system,a series of data tests were carried out on the laser illumination system of different Mn²⁺concentrations of Lu AG:Ce³⁺,Mn²⁺ceramics and different Gd³⁺concentrations of Lu_3-xGd_xAl₅O₁₂:Ce³⁺,Mn²⁺ceramics and blue laser combination,including color coordinates,Color temperature,display index,lumen rate.The results show that the highest color rendering index of Lu AG:Ce³⁺,Mn²⁺ceramics can reach 80.1,and the color temperature is 3298 K.The highest color rendering index of Lu_3-xGd_xAl₅O₁₂:Ce³⁺,Mn²⁺ceramics can reach 81.5,and the color temperature is 3465 K.Meet modern lighting quality requirements.