Study On Preparation And Application Of Rare Earth Doped Gadolinium Sulfide Up-conversion Luminescence Materials

Rare earth doped up-conversion luminescent materials have high stability,sensitivity,flexibility,and safety.As an inexpensive,environmentally friendly and recyclable up-conversion luminescent material,it has broad application prospects in the fields of infrared detecting,laser anti-counterfeiting,fingerprint identification and collection,etc.As is known to all,if the up-conversion material is to be practically applied and expects to have high up-conversion luminous efficiency,the selection of the matrix is very important.Gadolinium oxide sulfide(Gd₂O₂S)is an important rare earth sulfur oxide.As a luminescent material matrix,it has many advantages,such as high doping concentration of rare earth ions,excellent chemical stability,low toxicity and low phonon energy.Er³⁺ions have the characteristics of rich energy levels,long use time of metastable energy levels,good absorption of infrared bands,and narrower spectral bands.They are widely used in the field of solid-state lasers and anti-counterfeiting probes.While as for Yb³⁺ions,they have only one excited state ²F5/2,so they have quite high quantum efficiency,almost reaching 100%level.At the same time,Yb³⁺ions can absorb excellently the pumped energy and transfer it to the activator ions through the non-radiative process,because the infrared spectrum of Yb³⁺ions overlaps with that of Er³⁺ions.In summary,the activator selected in this paper is Er³⁺ion,and the sensitizer is Yb³⁺ion.At present,most studies on Gd₂O₂S:Er³⁺,Yb³⁺systems are mainly focused on 980 nm,and a few are focused on 1064 nm or 1550 nm.Therefore,this article mainly studies the best process parameters and best formulations of Gd₂O₂S:Er³⁺,Yb³⁺up-conversion luminescent materials that respond to three wavelengths.At the same time,the crystal structure and morphology,luminescence performance and luminescence mechanism of the best sample were explored.Then the screen was made by screen printing with Gd₂O₂S:Er³⁺,Yb³⁺phosphors.In order to obtain a portable high-efficiency multi-wavelength applicable infrared display detection board.In this paper,Gd₂O₂S:Er³⁺,Yb³⁺phosphors were synthesized by the high-temperature solid-state reaction method,and the following contents were mainly studied:(1)The influence of many factors on the preparation of phosphors by the high-temperature solid-state reaction method is analyzed by the controlled variable method.The optimum formula and technological parameters were determined preliminarily.The results show that the calcing temperature is 1025?,holding time is 4.5h,Er³⁺doping concentration is 14%,Er³⁺and Yb³⁺concentration ratio is 1:3,Na2CO3 is selected as flux.The sample washing method is to wash with deionized water,dilute hydrochloric acid(volume ratio:1:50),respectively,4 times,then wash with deionized water to neutral,wash once with absolute ethanol,filter with suction,and dry.(2)The optimum technological parameters and formula were optimized by orthogonal test.According to the comparison of the mean value and range of each factor and level,the best experimental conditions in four cases were selected by the intuitive analysis method.These four cases are the case where the luminescence effect is good under excitation at 980nm,1064 nm and 1550 nm respectively,and the case where the luminescence effect under excitation of three wavelengths is taken into account at the same time.Using XRD and refinement,the phase composition and parameter changes of the best samples that satisfy the three-wavelength luminescence effect are studied.The sample is hexagonal Gd₂O₂S phase.As Er³⁺-Yb³⁺enters Gd₂O₂S crystal and forms solid solution with it,no new phase is formed,which makes the cell smaller.Scanning electron microscope(SEM)showed that the grain size was about 300 nm and the morphology was regular.It has two yellow-green emission peaks at 530 nm and 550 nm,and the red emission peak at 670 nm,which belongs transitions of Er³⁺ions ²H_11/2?⁴I_15/2,⁴S_3/2?⁴I_15/2 and ⁴F_9/2?⁴I_15/2,respectively.The decay curves of the best samples at different temperatures(10K?300K)reflect the fluorescence lifetime of the best samples.It can be found that the fluorescence lifetime of the sample changes little at about 10K?100 K,and increases obviously at 100K-200 K,then decreases sharply with the temperature increasing from 200 K to 300 K.All these indicate that the Er³⁺ions ⁴S3/2 state luminescence lifetime of Gd₂O₂S:Er³⁺,Yb³⁺phosphors is sensitive to temperature.The main reason for the decrease of ⁴S3/2 state luminescence lifetime at 200K-300K is the non-radiative relaxation of ⁴S_3/2 state to ⁴F_9/2 state.(3)The Gd₂O₂S:Er³⁺,Yb³⁺phosphor screen was prepared by the screen printing method,and the effects of process parameters such as the number of printing times,the mass ratio of ink to powder and the amount of diluent added on the surface of the phosphor screen and the luminous performance were studied.With the increase of printing times,the thickness of the film increases and the incident light is absorbed more,which makes the luminous intensity increase accordingly;however,when the printing times are too many,the thicker the ink layer is,the coarser the screen surface is,resulting in the decrease of luminous intensity.When the amount of ink is too much,there will be wire drawing when scraping the screen;when the amount of ink is too little,it will make the experimental operation difficult,both of which will reduce the luminous intensity of the fluorescent screen.Therefore,when the substrate is cardboard and ceramic sheet,the number of screen printing is 8 is the most reasonable.When the substrate is PVC,the number of screen printing is 14 times,and the mass ratio of ink to powder is 1:1.5.Since the diluent has no effect on the luminous intensity,the addition amount of the diluent is chosen to be 1.5ml according to the conditions of this experiment.