Photoluminescence Behavior of Tb[sup 3+]-Activated YBO[sub 3] Phosphors

Abstract

The photoluminescence behavior of Tb-activated green phosphors has been studied for the last few decades. 1-3 But most of the efforts have been focused only on yttrium aluminum garnet (YAG):Tb phosphors, 4-11 which have been investigated for their application for projection TV. 7,8 The present investigation aims at elucidating photoluminescence properties of YBO 3 :Tb phosphor based on the possibility that this phosphor could be applied for plasma TV. The YBO 3 :Tb phosphor has a strong absorption band in the vacuum ultraviolet (VUV) range, and its luminance under VUV excitation is as high as conventional commercial green phosphors. In this regard, the YBO 3 :Tb phosphor is favorable for plasma TV. Even though the color chromaticity and decay time of (Y 1Ϫx Tb x )BO 3 phosphor still needs some improvement, this phosphor could be a potential candidate for the green component of plasma TV. Tb 3ϩ has a relatively simple energy level structure: low-energy state, 7 F j ( j ϭ 6,...,0) and excited states 5 D 4 and 5 D 3 leading to luminescence. Concentration quenching and also cross relaxation are very well known phenomena in Tb-activated phosphors, which arise in common, independent of the adopted host material. There are a lot of investigations dealing with these behaviors in YAG:Tb phosphors. 9-11 We confirmed that YBO 3 :Tb phosphor exhibits similar behavior but there is a slight difference in detail. In order to investigate in detail such behavior, YBO 3 :Tb phosphors with a wide range of Tb 3ϩ concentration from 5 ϫ 10 Ϫ4 to 5 ϫ 10 Ϫ1 were examined using several experimental skills. The excitation spectra together with diffuse reflectance spectra were first measured in the range between 100 and 350 nm, and then the emission spectra were measured both under VUV and UV excitations for various Tb 3ϩ concentrations. Time-resolved emission spectra were also obtained to examine the cross relaxation in a systematic manner. The decay curves of 5 D 4 -7 Fj and 5 D 3 -7 F j transitions are examined, respectively, and then analyzed to get to a better understanding of the decay mechanism for each transition.Experimental The materials used in the present investigation with the general formula (Y 1Ϫx Tb x )BO 3 have been prepared through the solid-state reaction for x values between 5 ϫ 10 Ϫ4 and 5 ϫ 10 Ϫ1 . The raw materials used, Y 2 O 3 , B 2 O 3 , and Tb 4 O 7 , are completely blended with a certain amount of acetone, dried, and fired at the temperature of 1200ЊC in a neutral atmosphere (in N 2 ). The firing process was then followed by a reduction process at 900ЊC by introducing the gas mixture of nitrogen and a small amount of hydrogen (2%) into the furnace so that a higher emission intensity can be obtained. Such a reduction process enhances the emission intensity by about 20%. The reduced powders were pulverized and then examined using Xray diffraction in order to check whether or not a single phase was obtained. The results confirm that the vaterite-like structure (hexagonal structure) is detected. 12-14 All the powder...

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