Preparation And Temperature Sensing Properties Of Er³⁺,Yb³⁺ Co-doped Germanate Up-conversion Phosphors

In recent years,germanate has been widely investigated because of its excellent properties such as high solubility of rare earth ions and low phonon energy.However,rare earth ion doped germanate upconversion phosphors are rarely reported.Therefore,it is significant to prepare upconversion phosphors based on germanate and study their luminescence properties and potential application.In addition,microcrystalline glass has the advantages of both ordinary glass and crystal,and has been widely studied.Based on the above discussions,the major work of this paper is to explore the luminescence properties and temperature sensing properties of Er³⁺,Yb³⁺co-doped germanate upconversion phosphor,and the luminescence properties of rare earth ion doped glass ceramics.The research contents are listed as follows:（1）A series of Y₄GeO₈:Er³⁺,Yb³⁺phosphors with different doping concentrations were successfully prepared by high temperature solid-state method,and their up-conversion luminescence and temperature sensing properties were studied.X-ray diffraction,scanning electron microscopy,diffuse reflectance spectrum and up-conversion emission spectrum under 980 nm excitation were used to systematically study the structure morphology and luminescence properties of the prepared samples.Under the excitation of 980 nm laser,samples doped with Er³⁺and Er³⁺,Yb³⁺all emit 525,545 and 656 nm light,which is due to the transitions of ²H_11/2,⁴S_3/2 and ⁴F_9/2 to ⁴I_15/2 of Er³⁺ions.With the incorporation of Yb³⁺,upconversion emission is enhanced by more than 15 times due to the greatly enhanced effective absorption at 980 nm.The mechanism of conversion luminescence on upconversion was discussed by power dependence and fluorescence attenuation curves.In addition,based on the Fluorescence Intensity Ratio（FIR）value of ²H_11/2/⁴S_3/2 of Er³⁺,the temperature sensing performances of the phosphor sample were studied.Y₄GeO₈:Er³⁺,Yb³⁺phosphors show suitable thermal coupling energy level difference(725 cm^–1),good relative sensitivity(up to 1.152%K^–1 at 303 K)and low temperature resolution（minimum 0.03 K at 303 K）.At the same time,the phosphor sample has excellent thermal stability.The above results indicate that the Y₄GeO₈:Er³⁺,Yb³⁺samples might have potential application prospects in the field of temperature measurement.（2）A new type of up-conversion phosphor composed of La₄GeO₈:Er³⁺,Yb³⁺was elaborated by high temperature solid state method.The emission spectra of La₄GeO₈:Er³⁺,Yb³⁺samples are mainly located at green region,which is attributed to the pair of thermal coupling energy levels of ²H_11/2 and ⁴S_3/2 of Er³⁺ions.After Yb³⁺ion was introduced,the up-conversion luminescence intensity of Er³⁺ion increased by more than 23 times.The mechanism of up-conversion luminescence was studied by power dependent spectra and fluorescence attenuation curves.The temperature measurement performance of the sample based on FIR technology is very excellent.The maximum relative sensitivity was 1.136%K^–1（303 K）.The minimum temperature resolution is 0.03 K.All the results show that La₄GeO₈:Er³⁺,Yb³⁺phosphors might have promising application in the field of high sensitivity optical temperature sensing.（3）YPO₄ glass ceramics doped with Dy³⁺were successfully prepared by melt quenching method and heat treatment.At 348 nm excitation,YPO₄:Dy³⁺glass ceramics emit blue light at 483 nm and yellow light at 575 nm.After heat treatment,the absorption intensity and emission intensity of Dy³⁺ions are significantly enhanced,indicating that the precipitation of YPO₄ microcrystals is beneficial to the luminescence enhancement of glass.In addition,the fluorescence lifetime of ⁶H_13/2energy level of glass-ceramics is also prolonged after heat treatment.The intensity of yellow emission is much stronger than that of blue emission,and different heat treatment temperatures have little effect on the color coordinates and color temperature of YPO₄:Dy³⁺glass ceramics.The above results indicate that the glass ceramics might have potential application prospect in yellow light emitting diodes.