Preparation And Upconversion Luminescence Property Of Ho³⁺/Yb³⁺/Tm³⁺-doped C12A7 Single Crystal

12Ca O·7Al2O3（C12A7）crystal is a kind of functional material with great integrated performance,which has wide application prospect on multicolor solid state laser and 3D display.In this dissertation,Ho³⁺/Yb³⁺/Tm³⁺ codoped C12A7 single crystal exhibiting upconversion white light have been successfully prepared,and the white emission mechanism is analyzed in detail.Mg²⁺ and Mn²⁺ are used to regulate the intensity and chromaticity of the upconversion white light,respectively.A series of Ho³⁺/Yb³⁺/Tm³⁺ codoped C12A7 polycrystals were synthesized by high temperature solid state method.Under 980 nm excitation,it appeared a blue upconversion emission at 477 nm,which corresponds to the transition: 1G4→3H6 of Tm³⁺,a g green emission centered at 550 nm corresponds to the transition: 5F4/5S2→5I8 of Ho³⁺,and red emission at 652 nm and 665 nm are from the Tm³⁺:1G4→3F4 and Ho³⁺:5F5→5I8 transition,respectively.Orthogonal test was used for discussing the relationship between the rare earth ion concentrations and the upconversion emission intensities in C12A7.Finally the white upconversion emission has been successful realized in Ho³⁺/Yb³⁺/Tm³⁺/C12A7 polycrystal.C12A7 single crystal doped with Ho³⁺/Yb³⁺/Tm³⁺ have been successful prepared by Czochralski method.The effects of the parameters during the crystal growth process on the crystalline quality have been discussed.Crysmas software was used for the temperature field simulations of different insulation thicknesses.The real temperature gradient was also measured to be compared with the simulation result,in order to build the most appropriate temperature field for the C12A7 crystal growth.CGsim software was used for the liquid surface shape simulation of the melt under different rotational speeds,in order to find the proper rotational speeds during the crystal growth process.ICP-MS test was used to find the relationship between the Ir4+ concentration in C12A7 and the O2 content of the growth gas phase.The orange color of C12A7 is from Ir4+ which is proved by the absorption spectra.Finally a set of process parameters for rare earth doped C12A7 growth have been summarized.XRD,UV-Vis absorption and upconversion luminescence spectroscopies are used to investigate the effects of RE ions concentrations on the structural and upconversion luminescence properties of C12A7 single crystal.The energy transfer between the rare earth ions is the main factor affecting the upconversion luminescence performance.The concentrations of Ho³⁺ and Yb³⁺ ions have great influences on the chromaticity of the output light color,and the light intensity is mainly changed by Yb³⁺ concentrations.Upconversion power curve,energy level lifetime test and steady state rate equation are used to investigate the white emission mechanism of C12A7 single crystal.Under 980 nm excitation,the 477 nm blue light is a three-photon continuous energy transfer process,the 550 nm green light and 652 nm/665 nm red light are both two-photon continuous energy transfer processes,and the photon required of the green light is a little bigger than the red one.The effects of excitation power on the upconversion white light of Ho³⁺/Yb³⁺/Tm³⁺/C12A7 single crystal were studied.With the increase of excitation power,the intensities of blue,green and red light are all enhanced,but the enhancement range is different.The CIE coordinates are shifted from the white light center to the blue-violet light boundary region,which is due to the high photon process of the blue light.The thermally coupled behavior of 3F2,3 and 3H4 energy levels for Tm³⁺ ion was discussed in C12A7 crystal.The results indicate that this kind of temperature sensor is suitable for temperature detection.The energy band structures of Yb³⁺ doped C12A7 and pure C12A7 single crystal have been calculated by first principle.It can be seen that the Yb³⁺ ions doping changes the energy band structure of C12A7,but does not change the Feimi level position.It proved that the rare earth ions do not enter in the cage structure,but exist by replacing Ca²⁺ ions.J-O parameters of Ho³⁺ and Tm³⁺ in C12A7 have been calculated,and the results indicate that C12A7 is suitable for realizing upconversion emissions.The effects of Mg²⁺ and Mn²⁺ on the upconversion white light of Ho³⁺/Yb³⁺/Tm³⁺/C12A7 single crystal were studied.The doping of Mg²⁺ ions has a good effect on the upconversion luminescence intensity of the Ho³⁺/Yb³⁺/Tm³⁺/ C12A7 single crystal.The doping of Mg²⁺ ions increases the lifetime of intermediate energy level and decreases the lifetime of luminous energy level,which reduces the photon number required during the upconversion process,and caused that the intensity of the white light is enhanced.The doping of Mn²⁺ions affects the number of Ho³⁺ ions on 5F5 level,which increases the emitting probability of red light.So the doping of Mn²⁺ ions has a good effect on the upconversion luminescence chromaticity of the Ho³⁺/Yb³⁺/Tm³⁺/C12A7 single crystal.