Luminescence from Pulsed-Laser-Deposited (Sr[sub 0.7]Ba[sub 0.3])[sub 2]SiO[sub 4]:Eu[sup 2+] Thin-Film Phosphors

Abstract

Thin-film ͑Sr,Ba͒ 2 SiO 4 :Eu 2+ phosphors were pulsed-laser deposited on quartz glass, sapphire, and Si wafers. The processing conditions were optimized to reduce substrate temperature during deposition and also to avoid high-temperature postdeposition annealing and reduction. In this study, the maximum processing temperature was reduced to 700°C, which must be lowered even further to produce on-chip phosphor films. The exact composition of the film obtained under the optimum processing conditions was identified by Rietveld refinement analysis, and two-peak emission behavior was investigated based on the exact structure.Thin-film phosphors have drawn considerable attention in an attempt to apply them to various display applications. 1-12 In fact, many sulfide and oxide thin-film phosphors have been developed for use in inorganic electroluminescent devices. Thin-film phosphors have advantages over powders in terms of their superior adhesion properties, high image resolution, good heat resistance, reduced outgassing, and long-term stability. In this regard, various deposition techniques have been employed in the production of thin-film phosphors, including radio frequency ͑rf͒ sputtering, pulsed laser deposition ͑PLD͒, pulsed electron-beam evaporation, and even sol-gel spin coating or spray pyrolysis. 1-12 In particular, thin-film phosphors developed by PLD are of great interest. 1-4 In addition to display applications, thin-film phosphors have been investigated for use in light-emitting diodes ͑LEDs͒. The preferred LED phosphor, Y 3 Al 5 O 12 :Ce 3+ ͑YAG͒ and its variants, already has been successfully developed in a thin-film form using rf magnetron sputtering and PLD techniques. 13,14 The YAG:Ce thin-film phosphors deposited by these techniques require high-temperature processing, either during or after the deposition. For example, at least 1200°C annealing after film deposition is required to achieve a complete crystallization of the YAG:Ce thin films. When the combination of thin-film YAG:Ce phosphors with InGaN chips is the object, breakdown of the InGaN chip at such high temperatures must be avoided.͑Sr,Ba͒ 2 SiO 4 :Eu 2+ phosphors, the luminance and color chromaticity of which are comparable to those of the YAG:Ce phosphor at blue LED excitations, 14-19 have attracted considerable attention for use in white-light-emitting diodes ͑WLEDs͒. Another merit of these phosphors is the ability to tune the emission peak by varying the Sr/Ba ratio. Despite their practical development in the powder form, there has been no attempt to achieve thin-film type ͑Sr,Ba͒ 2 SiO 4 :Eu 2+ phosphors. Our ultimate goal is to develop thinfilm ͑Sr,Ba͒ 2 SiO 4 :Eu 2+ phosphors with a processing temperature that can be lowered in the production of on-chip phosphor films, thereby avoiding breakdown of the InGaN chip. In this study we were not able to secure a processing temperature low enough to avoid InGaN chip breakdown. However, by lowering the maximum processing temperature ͑substrate temperature͒ as low as 700°C and by skipping th...

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

“…2b, because in any coordination system a barium ion is larger than a strontium ion by about 20%, which inflated the lattice and led to the peak shift. In particular, our previous structural study based on Rietvelt analysis 16 revealed that the addition of a large amount of barium elongated an axis ͑b-axis for Pmnb symme-try͒, while the others were not altered. When considering four major peaks located in the range 30.5-32°, such as ͑121͒, ͑022͒, ͑200͒, and ͑103͒ peaks, the effect of a large amount of barium, namely, the peak shift toward the small angle side, was only detected for the ͑121͒ and ͑022͒ peaks, while the ͑200͒ and ͑103͒ peaks coincided exactly with the standard data of non-barium-doped and small amounts of barium-doped samples, as shown in Fig.…”