A review on magneto-optical ceramics for Faraday isolators

As a promising magneto-optical(MO)material applied in Faraday isolators,magneto-optical ceramics possess excellent comprehensive properties and have attracted much attention these years.Herein,we review the fabrication and properties of magneto-optical ceramics including garnet,sesquioxide,and A_(2)B_(2)O_(7) ceramics.Some of the ceramics have been proved to possess applicable performance,while further studies are still needed for most of the magneto-optical ceramics.Aiming at the application for isolators,the research status,existing problems,and development trends of magneto-optical ceramics are shown and discussed in this review.

Composition and luminescence properties of highly robust green-emitting LuAG:Ce/Al_(2)O_(3)composite phosphor ceramics for high-power solid-state lighting

The major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance.However,phosphors usually suffer laser-induced luminescence saturation,which limits the peak luminance of laser lighting devices.The aim of the present study is to develop LuAG:Ce/Al_(2)O_(3)composite ceramics(LACCs)with a high saturation threshold for high-luminance laser lighting.Owning to the rigid crystal structure,proper synthetic process,and optimized thermal design,the LACCs possess small thermal quenching(16%loss in luminescence at 225℃),high quantum yield(>95%),and excellent luminescence properties.When the LACCs are irradiated by blue laser diodes in a reflection mode,a high luminous flux of 4634 lm and luminous efficacy of 283 lm·W^(−1)are realized.Furthermore,they show no sign of luminescence saturation even when the power density reaches 20.5 W·mm^(−2).With these favorable properties,the designed LACCs show great potential in high-luminance laser lighting.

Compositional regulation of multi-component GYGAG:Ce scintillation ceramics:Self-sintering-aid effect and afterglow suppression

(Gd,Y,Ce)_(3)(Y_(x)Ga_(1−x))_(2)GaAl_(2)O_(12)(GYGAG:Ce)scintillation ceramics with different Y excess,where x=0.005−0.08,were fabricated by the solid-state reaction method.The effects of stoichiometry on the phase composition,optical quality,and microstructure of GYGAG:Ce ceramics were analyzed.GYGAG:Ce ceramics have a pure garnet phase and obtain good in-line transmittance when x<0.04,while more Y excess leads to the creation of the secondary phase.The change of x value influences the sintering behavior of the GYGAG:Ce ceramics:The excess of Y works as the self-sintering aid and significantly reduces the sintering temperature of ceramics.When x=0.01–0.04,the X-ray excited luminescence(XEL)spectra and light yields of GYGAG:Ce ceramics are similar.The fast scintillation decay time and afterglow intensity of GYGAG:Ce ceramics show a slight decrease with increasing x value.Finally,additional 50–500 ppm MgO and 100–500 ppm CaO were introduced to the GYGAG:Ce ceramic with x=0.04,and both were found to significantly increase the fast scintillation component and reduce the afterglow intensity by two orders of magnitude to 0.01%after X-ray cut-off.

Fabrication and properties of non-stoichiometric Tb_(2)(Hf_(1-x)Tb_(x))_(2)O_(7-x)magneto-optical ceramics

Non-stoichiometric Tb_(2)(Hf_(1-x)Tb_(x))_(2)O_(7-x)(x=-0.07-0.45)magneto-optical ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing(HIP)posttreatment without any sintering aids.The phase composition,densification process,microstructure,optical transmittance,and Verdet constant of Tb_(2)(Hf_(1-x)Tb_(x))_(2)O_(7-x)ceramics were investigated.The in-line transmittance of(Tb_(0.93)Hf_(0.04))_(2)Hf_(2)O_(7.07)ceramics with a thickness of 2.0 mm reaches 74.6%at 1064 nm.The Verdet constant of Tb_(2)(Hf_(1-x)Tb_(x))_(2)O_(7-x)ceramics is-153.4,-155.8,and-181.2 rad/(T-m)at the wavelength of 633 nm when x=-0.07,0,and 0.1,respectively.The Verdet constant increases with the increase of Tb content,and these values are higher than that of the commercial Tb_(3)Ga_(5)O_(12) crystal,indicating that non-stoichiometric Tb_(2)(Hf_(1-x)Tb_(x))_(2)O_(7-x)ceramics have a great potential for the application in Faraday isolators.

Effect of Y substitution on the microstructure,magneto-optical,and thermal properties of(Tb_(1−x)Y_(x))_(3)Al_(5)O_(12)transparent ceramics

Faraday isolators can prevent the front-end system from disturbance and damage caused by a back-reflected beam,so they are important elements in laser systems.As magneto-optical materials are the most important component in Faraday isolators,the studies on magneto-optical materials have attracted much attention these years.Tb_(3)Al_(5)O_(12)(TAG)ceramics are considered to be one of the most promising magneto-optical materials for visible to near-infrared wavelength band application because of their outstanding comprehensive magneto-optical performance.However,the optical quality of TAG ceramics needs further optimization to meet the application requirements.In this work,high optical quality(Tb_(1−x)Y_(x))_(3)Al_(5)O_(12)(x=0,0.05,0.1,0.2,and 0.3)magneto-optical ceramics were fabricated successfully by solid-state reaction sintering combined with hot isostatic pressing(HIP)post-treatment.All the ceramics obtained showed a single garnet phase for different values of x in the range studied.The addition of Y2O3 was found to suppress the secondary phase and improve optical quality significantly.The ceramic samples obtained had clear grain boundaries and possessed the in-line transmittance values of 82.9%at 1064 nm and 82.2%at 633 nm,respectively.The Verdet constants of(Tb_(1−x)Y_(x))_(3)Al_(5)O_(12)ceramics with x=0,0.05,0.1,0.2,and 0.3 were−188.1,−175.4,−168.5,−143.0,and−119.9 rad/(T·m),respectively.The thermal conductivity of TAG ceramics was found to be 5.23 W/(m·K)at 25℃,and when 20%Y was substituted in place of Tb,the thermal conductivity decreased by only 9.4%.