Preparation And Temperature-sensitive Properties Of Rare Earth Doped Germanate Phosphor

Upconversion luminescent materials have attracted increasing interest as new luminescent materials due to their unique properties,such as adjustable emission bands,large anti-Stokes shifts and high penetration depth.The oxide-type upconversion luminescent materials have great potential applications in biomedicine,temperature sensing,anti-counterfeiting technology,based on the simple preparation process,stable physicochemical properties and excellent thermal stability.The hydrothermal method is an excellent material synthesis method with low preparation cost,better nucleation control and relatively mild operating conditions.In this paper,the germanate with relatively low phonon energy was selected as the host materials,and Yb³⁺/Er³⁺ion co-doped Sr Ge₄O₉,Ba Ge₄O₉,Ca₂Ge₇O₁₆ oxide upconversion luminescent materials were synthesized by hydrothermal method.The effects of ion doping concentration and pump power on luminescence intensity were studied.The upconversion energy transfer process and optical temperature sensitivity characteristics are analyzed in detail.Specific research contents and results include the following:（1）Preparation of materials,characterization of phase and morphology.Germanate upconversion phosphors with different doping concentrations were prepared by a one-step hydrothermal method.The impacts of rare earth ions doping concentrations on the phase and morphology of the host materials were analyzed.In particular,the growth mechanism of Sr Ge₄O₉ crystal was discussed.（2）Optimizing upconversion luminescence intensity by changing rare earth ion concentrations.The strongest upconversion luminescence was obtained by comparing the upconversion emission spectra of samples with different doping concentrations under 980 nm LD excitation:（Ⅰ）Sr Ge₄O₉:Yb³⁺/Er³⁺（8/1）sample has the strongest luminescence intensity under 980 nm LD excitation.（Ⅱ）Ba Ge₄O₉:Yb³⁺/Er³⁺（5/1）sample has the strongest luminescence intensity under 980 nm LD excitation.（Ⅲ）Ca₂Ge₇O₁₆:Yb³⁺/Er³⁺（8/1）sample has the strongest emission intensity under 980 nm LD excitation.（3）Studying the possible upconversion energy transfer mechanism.The possible upconversion luminescence mechanism and the photon absorption and emission processes were discussed in detail based on the study of the relationship between upconversion emission intensity and pump power.The green and red emissions of Sr Ge₄O₉:Yb³⁺/Er³⁺,Ba Ge₄O₉:Yb³⁺/Er³⁺,Ca₂Ge₇O₁₆:Yb³⁺/Er³⁺were mainly contributed by the two-photon process.（4）Discussing the temperature sensing behaviors of upconversion luminescence materials and the influencing factors.The upconversion spectra of Sr Ge₄O₉:Yb³⁺/Er³⁺,Ba Ge₄O₉:Yb³⁺/Er³⁺,Ca₂Ge₇O₁₆:Yb³⁺/Er³⁺phosphors based on fluorescence intensity ratio（FIR）were measured in the temperature range of 323 K～523 K.The optical thermometric ability of germanate upconversion phosphors was evaluated based on the measuring green emission intensity of Er³⁺thermally coupled levels as a function of temperature.The temperature resolution and repeatability of thermal-sensing readout were calculated.（Ⅰ）The maximum absolute sensitivity of Sr Ge₄O₉:Yb³⁺/Er³⁺（8/1）was0.0076 K^-1@523 K,the relative sensitivity was 0.0102 K^-1@323 K,and the temperature resolution was±1.28 K@323 K,±2.58 K@523 K.Repeatability was 98.1%@323 K and 97.1%@523 K.（Ⅱ）The maximum absolute sensitivity of Ba Ge₄O₉:Yb³⁺/Er³⁺（5/1）was 0.0073 K^-1@529 K,the relative sensitivity was 0.0100 K^-1@323 K,and the temperature resolution was±0.05 K@323 K,±2.75 K@523 K.Repeatability was98.6%@323 K and 96.7%@523 K.（Ⅲ）The maximum absolute sensitivity of Ca₂Ge₇O₁₆:Yb³⁺/Er³⁺（8/1）was 0.0061 K^-1@525 K,the relative sensitivity is 0.0102K^-1@323 K,and the temperature resolution was±1.27 K@323 K,±2.89 K@523 K.Repeatability was 98.4%@323 K and 97.0%@523 K.In addition,the possible reasons for the influence of Er³⁺ion doping concentration on the temperature sensitivity were discussed,according to variation regularities of temperature sensitivity aroused by Er³⁺ion concentration.The ytterbium and erbium co-doped germanate upconversion luminescence phosphors obtained in this study have good potential application in fluorescence temperature measurement.The research results also provide a reference for preparing rare earth ion doped oxide luminescence materials and designing optical temperature measurement materials.