Synthesis And Characterization Of Rare Earth Doped Orthophosphate Nanophosphors By Polyacrylamide Gel Technique

Rare earth doped orthophosphate nanophosphors were synthesized by apolyacrylamide gel technique. The phase structures, crystal sizes, morphologies,thermal properties and luminescence properties of the as-synthesized sampleswere characterized by X-ray diffraction (XRD), X-ray photoelectronspectroscopy (XPS), transmission electron microscopy (TEM), Scanningelectron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR),Thermal gravimetric analysis (TG-DSC) and Fluorescence spectroscopy (FL).The influence of the pH of the reaction system, the raw materialconcentration, the monomer and cross-linker concentrations, the adding order ofraw materials, the mass ratio of monomer (AM) and cross-linker (MBAM), thecalcination temperature and the mole ratio between RE (RE=Y and Tb) and P(n(Y+Tb)/n(P)) on the phase structures and luminescence properties of theas-prepared YPO4:Tb3+samples were investigated. The results reveal that theoptimum synthesis conditions of the synthetic of Tb3+doped yttriumorthophosphate fluorescent nano-materials by polyacrylamide geltechnique could be summarized as follows: the reaction system’s pH is6, theraw material concentration is0.1mol·L-1, the monomer and cross-linkerconcentrations are6.0g and1.0g, the mass ratio of monomer and cross-linker is6:1and the calcination temperature is750°C. Single-phase tetragonal xenotimestructure YPO4:Tb3+nanocrystals with crystallite sizes about6-10nm can beobtained in this way.The influence of the doping contents and different rare earth cations (RE=Tb3+, Eu3+, Ce3+) on the phase structures and fluorescence properties ofdoped/co-doped YPO4nanophosphors samples synthesis by a polyacrylamidegel technique were discussed. The results shown that the phase structures of theas-prepared samples doped with a certain contents of rare earth cations wereremain unchanged. The photoluminescence spectra show a characteristic greenemission of Tb3+for YPO4:Tb3+samples under ultraviolet light excitation. Aconcentration quenching phenomenon can be observed if the Tb3+dopingcontent was above6.0%in YPO4:Tb3+crystals. The excitation spectra ofYPO4:Eu3+samples show a dominating excitation band attributing to O2–-Eu3+ charge transfer (CT) transitions and some weak characteristic absorption bandsof Eu3+. The as-synthesized YPO4:Eu3+samples exhibit a characteristicorange-red light of Eu3+ions, and the critical quenching concentration is no lessthan6.0%. The emission of the YPO4:Ce3+samples would be quenched whenthe doping content of Ce3+is over0.4%. The excitation spectra of Ce3+/Tb3+co-doped YPO4samples show an strong characteristic excitation peak of Ce3+when monitor the characteristic emission band of Tb3+at547nm with thestrongest emission intensities. Such a phenomenon verified that the energytransfer process from Ce3+to Tb3+in Ce3+/Tb3+co-doped YPO4samples shouldexist. What’s more, the concentration quenching phenomenon could also beobserved when the doping contents of Tb3+is larger than6.0%for theco-doped system with a Ce3+-doping content of0.2%. And the decrease in thephotoluminescence intensity of Tb3+ions for Eu3+/Tb3+co-doped YPO4nanocrystals was observed when the doping contents of Eu3+was increased,attributing to the energy transfer process from Tb3+to Eu3+.The effects of the doping contents and different rare earth cations (Re=Tb3+,Eu3+, Ce3+) on the phase structures and fluorescence properties ofdoped/co-doped LaPO4nanophosphors were also investigated. The resultsreveal that the pure phase LaPO4crystals with monoclinic monazite structurecould be obtained and the matrix of the as-prepared samples would not changewith a small content of doped rare earth ions. Under UV excitation, theLaPO4:Tb3+samples emit a characteristic green light of Tb3+. And a quenchingphenomenon can be observed when increase the doping contents of Tb3+. It isinteresting to note that the critical quenching concentration for5D3→7F6transition is2.0%, and8.0%for5D4→7F5transition, respectively, arising fromthe cross relaxation from5D3level to5D4level of Tb3+. A characteristicorange-red emissions of Eu3+can be observed for the LaPO4:Eu3+samples anda concentration quenching phenomenon can’t be found when the dopingcontents of Eu3+is less than6.0%. The emissions of the LaPO4:Ce3+sampleswould be quenched when doping contents of Ce3+is larger than0.8%. Theconcentration quenching phenomenon can be appeared if the doping contents ofTb3+was increased to6.0%in the0.2%Ce3+co-doped matrix. The energytransfer process from Ce3+to Tb3+can also be revealed in Ce3+/Tb3+co-doped LaPO4nanocrystals. The characteristic green emissions of Tb3+ would be quenched when the doping content of Tb3+was up to4.0%in the0.5%Eu3+co-doped system.The Ce3+/Tb3+co-doped LaPO4nanophosphors were successfullysynthesized by a polyacrylamide gel process combined with a hydrothermalroute. The effects of conditions of hydrothermal treatment and calcinationtreatment on the phase structures and fluorescence properties were investigated.The results indicated that the monoclinic monazite structure of Ce3+/Tb3+co-doped LaPO4crystals could be easily obtained in the experimental conditions.The results revealed that the optimum prepared conditions are a pH of6, ahydrothermal temperature of140°C, a hydrothermal time of12hours, acalcination temperature of650°C for5hours.