(Y1-x-yPrxLay)InGe2O7 (x=0~0.2, y=0~0.2)系之光致發光特性研究

Abstract

In this study, YInGe2O7 germanate phosphor was selected as the host material. Pr3+ and La3+ ions co-doped YInGe2O7 phosphor were synthesized using a vibrating milled solid state reaction with metal oxides and calcined at 1200 °C for 10 h in air. The crystal structure, surface morphologies, and photoluminescence properties of the Y1-x-yPrxLayInGe2O7 phosphors were then investigated. For Pr3+ ion-doped YInGe2O7 phosphors, the XRD patterns show that all of the peaks are attributed to the monoclinic YInGe2O7 phase as the Pr3+ ions doped. The FE-SEM results show that there are no obvious differences for surface morphology of Pr3+-doped YInGe2O7 phosphors. There are two photoluminescence mechanisms for Y1-xPrxInGe2O7 phosphors: (a) host-activator transition, and (b) direct excitation of Pr3+ ion. By UV light 263 nm excitation, the emission spectra of (Y1-xPrx)InGe2O7 phosphors show a broad band between 350 to 480 nm, which is attributed to the emission of the YInGe2O7 host. A series of sharp emission peaks at 503, 530, 604 and 646 nm are assigning to the 3P0→3H4, 3P0→3H5, 1D2→3H4, 3P0→3H6 transition of Pr3+ ions, respectively. The optimal PL intensities is obtained for YInGe2O7 doped with 0.2 mol% Pr3+ ions, which has a CIE chomaticity coordinates of (x=0.321，y=0.286) located in the white region. Furthermore, under an excitation of 452 nm, the emission spectra of (Y1-xPrx)InGe2O7 phosphors show a dominant green emission peak at 503 nm, which is due to the 3P0→3H4 transition. The optimal PL intensity is obtained when the Pr3+ ion concentration is 5 mol%, and which is located in the green region with a CIE chomaticity coordinates of (x=0.168，y=0.499). In addition, in order to enhance the photoluminescence properties of YInGe2O7:Pr3+ phosphors, the La3+ ion is introduced to substitute Y3+ ion, and change thee lattice symmetry of Pr3+ ion as the Pr3+ ion concentration is fixed for 0.2 mol%. The emission spectra of (Y0.998-yLayPr0.002)InGe2O7 phosphors show a maximum intensity of emission peaks at 604 nm which was due to the 1D2→3H4 transition as the La3+ concentration increased. The results indicate that when the La3+ ion co-doped (Y0.998-yPr0.002)InGe2O7, the unit cell of lattice expands, but the partial Pr-O distance is decrease. The energy level splitting for 4f5d state increases which was due to the Pr3+ ion affected by a stronger crystal field. The larger crystal field caused the 4f5d state shifts to a lower energy state, and is closer to the 1D2 state of Pr3+ ion. High efficiency nonradiative transitions may populate the 1D2 state of Pr3+, leading the emission intensities of the 1D2→3H4 transition to increase. The optimal PL intensities is obtained when y=0.1 for (Y0.998-yLayPr0.002)InGe2O7 phosphor. When the La3+ ion is increased, which give rise the number of oxygen vacancies, but did not affect the luminescence properties of (Y0.998-yLayPr0.002)InGe2O7 phosphor. Proper amount of oxygen vacancy is commonly regarded, and dramatically promotes the energy transfer as a sensitizer resulting in an increase of PL intensities. However, when the La3+ concentration increases further, a more asymmetrical structure leads the oxygen vacancies to increase and a second phase form, excessive oxygen vacancies will be generated, then results the luminescence to quench. The CIE chomaticity coordinates of (x=0.408，y=0.330) shift to the warm white light region as the La3+ concentration increases.