The Effect of Tb[sup 3+] Co-Doping on the Photoluminescence of (Sr,Ba)[sub 2]SiO[sub 4]:Eu[sup 2+]

Abstract

We introduced Tb 3+ co-dopants into well-known orthosilicate phosphors such as Sr 2 SiO 4 :Eu 2+ and ͑Sr,Ba͒ 2 SiO 4 :Eu 2+ . Tb 3+ co-doping had a positive influence on the overall photoluminescence ͑PL͒ intensity of ␤-Sr 2 SiO 4 :Eu 2+ , Tb 3+ and ␣Ј-͑Sr 0.7 Ba 0.3 ͒ 2 SiO 4 :Eu 2+ , Tb 3+ . In the absence of barium incorporation, Tb 3+ co-doping induced phase transformation of the Sr 2 SiO 4 host from the ␤ to the ␣Ј phase, such that the peak location redshifted and the peak intensity decreased significantly. For ␤-Sr 2 SiO 4 :Eu 0.02 2+ and ␣Ј-͑Sr 0.7 Ba 0.3 ͒ 2 SiO 4 :Eu 0.02 2+ , we detected inactive energy transfer from Eu 2+ to Tb 3+ , despite the fact that the PL intensity was improved by the Tb 3+ co-doping, meaning that the Eu 2+ emission never decreased as the Tb 3+ concentration increased. There was clear evidence supporting an energy transfer between Eu 2+ and Tb 3+ for ␣Ј-Sr 2 SiO 4 :Eu 2+ , Tb 3+ despite no conspicuous practical improvement in the PL properties. The positive influence of Tb 3+ co-doping comes not from the energy transfer, but, rather, simply from the local structure change around the Eu 2+ activator in the host. Divalent europium-doped orthosilicates have attracted considerable attention as promising phosphors since their application to light emitting diodes ͑LEDs͒ 1-5 . Even after the advent of various, more promising, nitride phosphors, 6-10 the orthosilicate phosphor still serves as a key phosphor in some commercially available white LEDs. To achieve successful use in LED applications, barium and strontium were incorporated together into an ␣Ј-Sr 2 SiO 4 structure, and there has been no further alteration of the basic ␣Ј-͑Sr,Ba͒ 2 SiO 4 composition. However, recent Tb 3+ co-doping reportedly had a positive influence on the photoluminescence ͑PL͒ of ␣Ј-͑Sr,Ba͒ 2 SiO 4 :Eu 2+ , Tb 3+ . 11,12 Hiramatsu et al. 11,12 argued that a brisk energy transfer takes place between Eu 2+ and Tb 3+ in the ␣Ј-͑Sr,Ba͒ 2 SiO 4 host and the energy transfer leads to a positive impact on the LED function. It is true that a certain degree of energy transfer obviously occurs in the ␣Ј-͑Sr,Ba͒ 2 SiO 4 :Eu 2+ , Tb 3+ system. However, the composition of the ␣Ј-͑Sr,Ba͒ 2 SiO 4 :Eu 2+ , Tb 3+ system that Hiramatsu et al. 11,12 adopted deviated from the conventional composition, especially in terms of Eu 2+ activator concentration. These researchers adopted a relatively low Eu 2+ activator concentration, such that the effect of the energy transfer between Eu 2+ and Tb 3+ could be slightly exaggerated. To make the Tb 3+ co-doping induced energy transfer contribute to the improvement in the PL intensity and color chromaticity and, hence, to secure a higher practicality, we introduced Tb 3+ co-doping along with a higher, more realistic Eu 2+ activator concentration level. Also, we examined the Tb 3+ co-doping effect separately for both the ␣Ј-and ␤-Sr 2 SiO 4 structures. Namely, we introduced Tb 3+ co-doping into ␣Ј-Sr 2 SiO 4 :Eu 0.02 2+ , ␤-Sr 2 SiO 4 :Eu 0.02 2+ , and ␣Ј-͑Sr 0.7 Ba 0.3 ͒ 2 SiO 4 :Eu 0.02 2+...

Photoluminescent properties of ZrO2: Tm3+, Tb3+, Eu3+ powders—A combined experimental and theoretical study

“…The Energy transfer (ET2) between Tb 3+ and Eu 3+ has been extensively studied, in order to understand the photoluminescent behavior [78]. In fact, the luminescence intensities of various rare-earth ions can be enhanced or quenched by the energy transfer from other co-doped rare-earth ions [79][80][81]. ET2 between Tb 3+ and Eu 3+ may occur in hosts, such as tungstates, zeolite-Y, yttria, porous silicon, borate, hydrate, and molybdates [82][83][84][85].…”

CaGdAlO4:Tb3+/Eu3+as promising phosphors for full-color field emission displays

“…37 When doping with different concentrations of Tb 3+ in the host matrix, the transitions of 5 D 3 or 5 D 4 to 7 F J may produce blue or green emissions. 38,39 Fig. 3 shows a representative excitation and emission spectra for CaGdAlO 4 :0.05Tb 3+ at room temperature.…”

Nanocrystalline CaYAlO4:Tb3+/Eu3+ as promising phosphors for full-color field emission displays

“…It has been recognized that the luminescence intensities of various rare-earth ions can be enhanced or quenched by the energy transfer from other codoping rare-earth ions. 32,[45][46][47][48] For example, an energy transfer can take place from Tb 3+ to Eu 3+ when they are codoped in one host, such as tungstates, zeolite-Y, yttria, porous silicon, borate, hydrate, and molybdates. [49][50][51][52] So far, little information is available on Tb 3+ , Eu 3+ -codoped CaYAlO 4 .…”