| Rare earth ions doped luminescence materials excited by120-420nm have important application in many fields, and have been studied widely. One hand, the luminescence materials excited by vacuum ultraviolet (VUV) can be applied in the field of plasma display panels (PDPs) and Hg-free lamps. In recent years, with the development of three-dimensional (3D) display, the application range of VUV luminescence materials have been extended because of their higher response speed. Therefore, better qualities of VUV excited phosphors have been required during application, such as thermal stability, color purity, decay time, luminescence efficiency, and so on. Besides, the luminescence mechanisms of VUV excited phosphors have not been clear until now, which would result in the waste of materials while exploring new materials. Thus, the investigation on luminescence mechanism is also significant and important. On the other hand, the luminescence materials excited by near-UV photons can be used on white light-emitting diodes (LED), and some special requirements are also needed at the same time, containing high brightness, strong absorption in the region of near-UV and so on. According to above discussion, some kinds of luminescence materials excited by120-420nm have been designed and synthesized, and the luminescence properties have also been investigated in detail.The main results have been listed as below.(1) The Ca2Gd8(SiO4)6O2:Ln3+(Ln=Eu, Tb, Dy) were investigated under VUV excitation. The Ca2Gdg(SiO4)6O2:Eu3+shows a red emission when excited by147nm, and the concentration quenching happened when8%Eu3+was introduced into the Ca2Gdg(SiO4)6O2host. Meanwhile, electric dipole transition5D0â†'7F2in emission spectra of Ca2Gds(SiO4)6O2:Eu3+implies that Eu3+ions occupy non-centro symmetric sites of Gd3+. For Ca2Gd8(SiO4)6O2:Tb3+. When monitored at the5D4â†'7F5emission(λcm=544nm) of Tb3+, the transition of8S7/2â†'6G1,8S7/2â†'6DJ from Gd3+appear, implying that the Gd could efficiently transfer the absorbed energy to Tb3+For the Ca2Gds(1-x)(SiO4)6O2:Dy3+, the peaks at166nm and191nm of the vacuum ultraviolet region in the excitation spectrum can be assigned to the O2-â†'Gd3+charge transfer band (CTB), and O2-â†'Dy3+CTB respectively. All the samples exhibited excellent white emission under172nm excitation and the best calculated chromaticity coordinate was (0.335,0.338), which indicates that the phosphor of Ca2Gdg(SiO4)6O2:Dy3+could be considered as a potential candidate for Hg-free lamps application.(2) The VUV excited luminescent properties of Eu3+, Tb3+, Dy3+, Sm3+and Tm3+in the matrices of Ca4Y6(SiO4)6O were investigated. The bands at about173nm in the VUV excited spectra were attributed to host lattice absorption of the matrix Ca4Y6(SiO4)6O. For Eu3+-doped samples, the O2-â†'Eu3+CTB was identified at258nm. Typical4f-5d absorption bands in the region of195-300nm were observed in Tb3+-doped samples. For Dy3+-doped and Sm3+-doped samples, the broad excitation bands consisted of host absorptions, CTB and f-d transition. For Tm3+-doped samples, the O2-â†'Tm3+CTB was located at191nm. About the color purity and emission intensity, Ca4Y6(SiO4)6O:Tb3+is an attractive candidate of green light PDP phosphor, and Ca4Y6(SiO4)6O:Dy3+has potential application in the field of mercury-free lamps.(3) The Gd9.33(SiO4)6O2:Re3+(Re=Eu, Tb) samples were synthetized and investigated for the first time. In the excitation spectrum of Gd9.33(SiO4)6O2:Eu3+, two O2-â†'Eu3+CTBs were observed, and the one (λ1=229nm) is from the Eu3+at4f sites of Gd3+, the other one (λ1=267nm) is from the Eu+at6h sites of Gd3+. Under172nm excitation, the splitting number of the5D0-7FJ (J=0,1,2) is over1,3,5, respectively, further demonstrating that the Eu3+occupying two sites in Gd9.33(SiO4)6O2. At the same time the excitation peaks of Gd3+(273nm,313nm) could be observed when Eu3+emission is monitored, implying the energy transfer exists from Gd3+to Eu3+. In the Gd9.33(SiO4)6O2:Tb3+, the quantum cutting was observed and proved, thus the Gd9.33(SiO4)6O2:Tb3+has the potential application in the field of the PDP phosphor.(4) The potentiality of Ce3+and Tb3+co-doped Ca4Y6(SiO4)6O phosphors was studied. By incorporation of Ce3+into, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The Ca4Y6(SiO4)6O:Tb3+energy transfer from Ce3+to Tb3+in Ca4Y6(SiO4)6O host was investigated and demonstrated to be a resonant type via a dipole-dipole mechanism with the critical distance of10.2A. When excited by352nm, Ca4Y6(SiO4)6O:Ce3+, Tb3+exhibited a brighter and broader violet-blue emission (421nm) from the Ce3+and an intense green emission (542nm) from the Tb3+. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278,0.353) is generated in Ca4Y6(SiO4)6O:2%Ce3+,8%Tb3+, and this phosphor could be potentially used in near-UV LEDs.(5) Novel red phosphors Na(Y1-xEux)(Si1-yMoy)O4were developed for white LEDs applications and their luminescent properties were investigated in detail. The results indicated that NaY1-xEuxSi04samples can be effectively excited by near-UV light (393nm) and the introduction of Mo6+strongly enhanced the emission intensity of Eu3+when samples were excited under393nm, which was ascribed to the improvement of absorption intensities of7F0â†'5L6transitions. Besides, the quantum efficiencies of a series of Na(Y1-xEux)(Si1-yMoy)O4samples were calculated according to the average decay lifetimes. The composition-optimized Na(Yo.7Euo.3)(Sio.7Moo.3)04sample exhibited the red light emission brightly with the chromaticity coordinates of (0.66,0.34), whose integral intensity was calculated to be about2.16times of that of the commercial red phosphor Y2O3:Eu3+. Thus, Na(Y1-xEux)(Si1-yMoy)O4can be as red-phosphor candidates for white LEDs devices.(6) A blue-emitting borophosphate KSrBP2O8:Eu2+is synthesized and evaluated as a candidate for near ultraviolet white LEDs. This phosphor shows strong excitation band in250-420nm, and a broad and asymmetry emission band with a tail on the long-wavelength side. According to investigating on the crystal structure, the asymmetry emission band results from the certain degree of substitutional disorder of Eu2+in KSrBP2O8:Eu2+. The emission intensity of the optimal sample with5%Eu2+is reached to89%of that of the commercial BaMgAl10O17:Eu2+under excitation at365nm, and the quantum efficiency of the optimal sample is48.9%. The results reveal that the potential application of KSrBP2O8:5%Eu2+as a blue-emitting UV convertible phosphor for white LEDs is feasible.(7) The series of the KSrBP2O8:x Dy3+(0.01≤x<0.05) were firstly studied. Along with the increase of the Dy3+, the chromaticity coordinates of the KSrBP2O8:x Dy3+(0.01<x<0.05) changed obviously. Through co-doping the Tm3+, a good white light could be obtained in KSrBP2O8:3%Dy3+,0.5%Tm3+when excited by356nm, and the chromaticity coordinate was calculated to be (0.331,0.324). Thus the KSrBP2O8:3%Dy3+,0.5%Tm3+has a good potential application in NUV pumped W-LEDs. |
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