绿色荧光粉LaGaO3∶Tb3+,Sn4+的制备及发光性能研究

doi:10.3964/j.issn.1000-0593(2020)01-0065-06

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Abstract Rare earth doped LaGaO₃ phosphors could be suitable for use in field emission display and LED applications, owing to the excellent luminescent properties, high color rendition and stability, et al. The luminescent intensity and color purity of LaGaO₃∶Tb³⁺ are higher than those of commercial Y₂SiO₅∶Ce³⁺ phosphor. In order to expand application in white LED, the luminescent intensity of LaGaO₃∶Tb³⁺ is enhanced by co-doping Sn⁴⁺ ions in this paper. A series of green phosphor LaGaO₃∶Tb³⁺ and LaGaO₃∶Tb³⁺,Sn⁴⁺ were synthesized by high-temperature solid-state method. The crystal structures and luminescent properties were characterized by XRD and photoluminescence spectrum, respectively. The results show that all Tb³⁺ and Sn⁴⁺ ions preferably substitute for La³⁺ and Ga³⁺ ions, respectively, in the crystal lattice of LaGaO₃ without impurity phases, indicating obtained samples are single phase phosphors. All excitation spectra consist of some broad peaks (231, 257, and 274 nm) and sharp peaks (from 300 to 500 nm). The bands at 231 and 274 nm are assigned to the spin allowed transition (LS, ⁷F₆→⁷D_J, ΔS=0) and the spin forbidden transition (⁷F₆→⁹D_J, ΔS=1) for 4f-5d of Tb³⁺, respectively. The band at 257 nm is assigned to the transition of a self-activated optical center related to octahedral coordinated GaO₆ groups. Some excitation peaks in the range of 300～500 nm are attributed to f-f characteristic transitions of Tb³⁺, such as ⁷F₆→⁵H₆, ⁵H₇, ⁵L₆, ⁵L₉, ⁵L₁₀, ⁵G₉ and ⁵D₄. Compared with LaGaO₃∶Tb³⁺, co-doped Sn⁴⁺ion can enhance the 4f-4f characteristic excitation intensity of Tb³⁺. The main excitation peak changes from f-d transition of Tb³⁺ to its f-f transition. Under excitation at 308 nm, the emission spectra of LaGaO₃∶Tb³⁺ and LaGaO₃∶Tb³⁺,Sn⁴ all consist of Tb³⁺ ions characteristic transitions, such as ⁵D₄→⁷F₆ (487, 493 nm), ⁵D₄→⁷F₅ (545 nm), ⁵D₄→⁷F₄ (584, 589 nm), and ⁵D₄→⁷F₃ (622 nm). The strongest emission peak is at 545 nm. The CIE color coordinates of LaGaO₃∶Tb³⁺ and LaGaO₃∶Tb³⁺,Sn⁴⁺ are (0.287 4, 0.545 9) and (0.279 7, 0.576 1) in green region, respectively. The fluorescence lifetime of LaGaO₃∶Tb³⁺ and LaGaO₃∶Tb³⁺,Sn⁴⁺are 1.63 and 1.38 ms, respectively；the color purity values of LaGaO₃∶Tb³⁺ and LaGaO₃∶Tb³⁺,Sn⁴⁺ are 54.81% and 62.67%, respectively. Co-doped Sn⁴⁺ ion has no impact on the position of emission peaks, but the emission intensity of Tb³⁺ increases to nearly double. Mechanism of concentration quenching can be changed from dipole-quadrupole (d-q) to quadrupole-quadrupole (q-q) interactions. The optimum doping concentration of Tb³⁺ is 0.05 and 0.07 in the LaGaO₃∶Tb³⁺and LaGaO₃∶Tb³⁺,Sn⁴⁺, respectively. The optimum Sn⁴⁺ doping concentration is 0.03. The optimum doping concentration of Tb³⁺ increases by co-doped Sn⁴⁺, which is beneficial to improving luminous intensity. The luminous efficacy values of the radiation (LER) of LaGaO₃∶0.05Tb³⁺ and LaGaO₃∶0.07Tb³⁺, 0.03Sn⁴⁺ are 464 and 485 lm·W^-1, respectively. The internal quantum efficiency values of LaGaO₃∶0.05Tb³⁺ and LaGaO₃∶0.07Tb³⁺, 0∶03Sn⁴⁺ are 21.8% and 39.2%, respectively. The emission intensity decreases gradually with the increasing temperature due to the thermal quenching. The emission intensity of the LaGaO₃∶Tb³⁺,Sn⁴⁺ sample remains to be above 70% at 150 ℃. According to the Arrhenius equation, the thermal activation energy ΔE for quenching is calculated to be 0.169 0 eV, which indicates that this phosphor has excellent thermal stability. All the results show that the LaGaO₃∶Tb³⁺,Sn⁴⁺ phosphor is a promising green phosphor for the n-UV excited w-LEDs.

Key words：Green phosphors; Luminescence; LaGaO₃∶Tb³⁺,Sn⁴⁺

Received: 2018-11-16 Accepted: 2019-03-20

ZTFLH:

O482.31

Corresponding Authors: ZHAO Wen-yu E-mail: zhaowenyu2011@hotmail.com

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2020)01-0065-06 OR https://www.gpxygpfx.com/EN/Y2020/V40/I01/65