Preparation And Luminescent Properties Research On Nanocrystallites Of Baddeleyite And Phosphatic Mineral

Mineral luminescence was first researched by human over the history ofluminescence. Considering most of the researches on mineral mainly belong to thescope of geology, mineral luminescence were sometimes used to solve theproblems in geology, such as the formation mechanism of mineral, determinationon geologic age of mineral or rock, and so on. However, mineral usually contains alarge amount of impurities significantly quenching the luminescence, which wastherefore far away from the practical applications. Based on the luminescentfeatures of mineral, people have synthesized many kinds of luminescent materialsat laboratory. In addition, the rare earth ions with rich energy levels often act asactivators to enhance the luminescence, so rare earth doped mineral were alsoprepared and applied in a wide range.In contrast with bulk materials, nanomaterials possess many particularproperties, for example, small size effects, surface and interface effects, quantumconfined effects, macroscopical quantum tunnel effects and dielectric confinedeffects, etc. With the development of namoscience and nanotechnology, thenano-sized luminescent mineral has received much attention over last few years,which were expected to exhibit many novel optical, catalytic and photochemicalproperties, especially the case of rare earth doped nanocrystals which have beenbeing a research issue.Baddeleyite (ZrO₂) as excellent host matrix have been extensively used inlight and display fields due to its superior mechanical, thermal, optical and electricproperties including high refractive index, optical transparency and chemicalstability as well as low phonon energy, etc. However, up to now, the studies of rareearth doped baddeleyite nanocrystals were rare. Rosa-Cruz group recently studiedthe spectroscopic features of ZrO2 : Sm3+ nanocrystals and observed energy transferprocess. Note that Dy3+ is a promising activator of bicolor phosphors. But ZrO2:Dy3+ nanometer phosphors have not been reported in our homeland. In this paper,we prepared ZrO2: Dy3+ nanocrystals by coprecipitation method and studied thephotoluminescent properties in detail.Rare earth orthophosphate (LnPO4) is an important class of host matrix forgreen emitting phosphors due to its better chemical stability, which has beenextensively used in thermally induced luminescence materials, glitter object andlaser. For higher vacuum ultraviolet (VUV) absorption efficiency of PO43-andeffective energy transfer between Eu3+ and Gd3+, GdPO4: Eu3+ was expected to becandidate phosphors in plasma display panels (PDPs). In this paper, we preparedone dimensional GdPO4: Eu3+and GdPO4: Eu3+, Tb3+ nanowires by hydrothermalmethod and studied the photoluminescence properties in detail.It is well known that Tb3+ is the most important activator in green emittingphosphors, Tb3+ activated phosphors have been widely used in fluorescent lamp,cathode ray tube (CRT) and X-ray enhancing induction screen. More importantly,Ce3+ ion has broad band absorption and is an effective sensitizer of Tb3+luminescence. Higher luminescence efficiency of Tb3+ can therefore be obtained byenergy transfer from Ce3+ to Tb3+, Ce3+ and Tb3+ co-activated phosphors have beenextensively applied in fluorescent lamp, cathode ray tube (CRT) and X-rayenhancing induction screen for many years. The energy transfer process betweenCe3+ and Tb3+ in bulk crystals was studied in detail, but was rare in nanocrystals. Inthis paper we prepare one dimensional GdPO4: Eu3+, LaPO4: Tb3+ and LaPO4: Ce3+,Tb3+ nanowires and microrods and study their luminescent properties in system,and discuss the differences of luminescent characteristics between one-dimensi-onal nanowires and zero-dimensional nanoparticles and corresponding macrosco-pical crystal material.Primary productions of this paper were given as below:Monoclinic phase ZrO2:Dy3+ nanocrystals are prepared by co precipitationmethod, which are spherical particles in narrow size distribution. The size was inthe 20-30 nm range after annealing at 800℃ and increased to approximately 100nm after thermal treat at 1200 ℃. Broader excitation and emission bands wereobserved, corresponding to the electron transition between valence band andconduction band. The luminescence intensity of Dy3+ doped sample increases withthe size. Li+ and Dy3+ codoped sample has stronger emissions. With the variation ofDy3+ concentration, the intensity ratio of orange emissions to blue emissionschanged. The concentration quenching was induced by exchange interaction amongadjacent activators.Eu3+and Tb3+ codoped GdPO4 nanowires, micrometer rods and nanoparticleswere prepared by a hydrothermal method. we studied the dependence of tempe-rature and pH values on size and morphology of nanocrystal. The results indicatethat when pH equals to 1, temperature is at 130℃ it mainly yields micrometer rods;when pH equals to 9, it generates zero dimension amorphous nanoparticles;whenpH equals to 5 and 13, nanowires were formed;the sample prepared at tempreature160℃ is micrometer rod when PH equals to 1 and nanowire when PH value is 13.And PH value affects the shape and dimension greatly for the same tempreature,while the temperature has little obvious effect on the shape. The nanocrystals canbe indexed in monoclinic phase. The optical characterization show that, the chargetransfer band of Eu in sample obtained at pH =13 shift to the bule clearly due to theshortening of Eu-O distance. The intensity ration of 5D0-7F2/5D0-7F1 increased innanoparticles, but did not change obviously in other samples. Stronger greenemissions were observed in GdPO4: Tb, and energy transfer from Gd to Eu and Tbwas observed in GdPO4: Tb, Eu.LaPO4: Ce3+, Tb3+ nanowires and micrometer rods were prepared by ahydrothermal method. nanowires synthesized at 120℃ was with the diameter of10-20nm and with length of 500nm. The high aspect ratio increased with thehydrothermal temperature. Microrods was synthesized at 150℃ with the diameterof 100-200 nm and length of 1-2μm. We studied the photoluminescence propertiesin detail. The results indicate that the energy transfer rate of Ce3+ to Tb3+ innanowires was lower than the case of microrods, but energy transfer producedintense 5D4-7F5 transitions, as a result, the green emissions increase by a factor of3-5, which was attributed to the smaller energy loss at higher excited levels above5D4 arising from the boundary hindrance.The above researches on rare-earth doped namometer mineral havesignificantly theoretical and practical sense for us to develop new type of mineralfunction material.