Preparation And Properties Modulation Of YAG-based Fluorescent Ceramics For High-quality Laser Illumination

Visible laser lighting technology is developing rapidly,the lifetime,luminous intensity and efficacy of the related lighting devices depend on the inorganic fluorescent conversion materials,which are the key components.In comparison with single crystal and glass,fluorescent ceramics have excellent structural tunability as well as optical and thermal properties,making them a new generation of inorganic fluorescent conversion materials with great potential for application.Yttrium aluminum garnet（YAG）based fluorescent ceramics have been the mainstream materials for combining with blue LED chips due to their simple preparation and low cost,and the"open and inclusive"structural characteristics of YAG provide the possibility of multi-lattice doping.In this study,yellow YAG:Ce was used as the main subject,given the inherent defects of lacking long-band red components in its emission spectrum and the not broad enough,high-quality YAG-based transparent fluorescent ceramics were prepared by a combination of solid-phase reactions and vacuum hot-pressure sintering through matrix modulation and red-emitting ion supplementation,and their microstructure characteristics and optical properties were explored.The main study and findings are listed below:（1）From the perspective of YAG matrix modulation,Mg²⁺and Si⁴⁺ions were introduced on the basis of YAG:Ce to optimize the luminescence range of YAG:Ce transparent ceramics,and we first explored the sintering temperature of YMASG:Ce under the hot-pressure system.During the sintering process,using the hot-pressure sintered carbon contamination treatment method,combined with the thermogravimetric-differential thermal analysis of the mixed powder before calcination and the thermal expansion curve of the ceramic green body,the optimal hot-pressure sintering temperature of the YMASG:Ce system was considered to be 1500°C,at which the YAG phase reaction was fully completed and the pure phase YAG lattice structure was obtained with excellent microscopic morphological characteristics.The sample achieved an in-line transmittance of 50.9%at 800 nm and showed good fluorescence emission performance.This experiment has improved the basic conditions for the subsequent study.（2）The effect of Mg²⁺-Si⁴⁺doping in YMASG:Ce on the structure and properties of the ceramics was investigated based on determining the hot-pressure sintering temperature of YMASG:Ce,and the doping amount of Ce³⁺was further optimized.It was shown that the highest in-line transmittance of 67%at 800 nm was achieved for the x=0.3 sample in the Y₃(Mg_xAl_5-2xSi_x)O₁₂:Ce（x=0.3-1.5）system.The introduction of the Mg²⁺-Si⁴⁺ion pair intensified the crystal field splitting of Ce³⁺in YAG:Ce,as manifested by the fact that the red region of the emission spectrum of YMASG:Ce fluorescent ceramics was effectively broadened with the increase of the Mg²⁺-Si⁴⁺doping amount,and the color coordinates gradually shifted to the orange-red region,and warm light output with CRI up to 70 and CCT of 2823 K was obtained for the x=1.5 sample.Therefore,Mg²⁺-Si⁴⁺double doping was beneficial for improving the emission spectra of Ce³⁺,enhancing the color rendering and effectively reducing the CCT.The results of(Ce_xY_1-x)₃（Mg Al₃Si）O₁₂（x=0-0.005）showed that an appropriate amount of Ce³⁺doping was effective in improving the densities and optical transmittance of YMASG:Ce fluorescent ceramics,and with the increase of Ce³⁺doping,the emission peak of the sample was shifted by 21 nm toward the long wavelength with the excitation at 460 nm and the full width at half maxima was expanded.In contrast,the x=0.001 sample exhibited the optimal full-spectra emission with a warm orange output light and its CRI was as high as 70.1 and CCT was 2746 K.（3）In terms of red light emission ion doping,YAG:（Ce,Cr）,YAG（Ce,Pr）and YAG:（Ce,Pr,Cr）transparent fluorescent ceramics with varying ion doping were obtained by vacuum hot-pressure sintering method.The analysis combined with the YAG:Ce samples prepared under the same conditions suggested that all samples had a pure YAG phase structure,along with neat grain boundaries and grain sizes of about1-4μm.For optical properties,the Pr³⁺-doped sample had the maximum transmittance at 800 nm,which was improved by 13.7%compared to the YAG:Ce sample.According to the fluorescence spectra,Ce³⁺,Pr³⁺and Cr³⁺could be excited by blue light at 460 nm at the same time,and there was a feasible energy transfer between Ce³⁺and Cr³⁺or Pr³⁺,respectively.The electroluminescence tests revealed that samples doped with red light-emitting ions had a wider spectral range than YAG:Ce,especially the spectrum of Ce Cr and Ce Pr Cr samples covered almost the full visible light range.The doping of Pr³⁺and Cr³⁺had a positive effect on supplementing YAG:Ce red light emission.