Abstract
Although inorganic crystalline phosphors can exhibit high quantum efficiency, their use in phosphor films has been limited by a reliance on organic binders that have poor durability when exposed to high-power and/or high excitation energy light sources. To address this problem, Sn2+ -doped transparent phosphate films measuring several micrometers in thickness have been successfully prepared through heat treatment and a subsequent single dip-coating process. The resulting monolithic inorganic amorphous film exhibited an internal quantum efficiency of over 60% and can potentially utilize transmitted light. Analysis of the film’s emissivity revealed that its color can be tuned by changing the amount of Mn and Sn added to influence the energy transfer from Sn2+ to Mn2+. It is therefore concluded that amorphous films containing such emission centers can provide a novel and viable alternative to conventional amorphous films containing crystalline phosphors in light-emitting devices.
Highlights
Recent advances in light-emitting diodes (LEDs) have been accompanied by the development of new phosphors[1,2,3,4,5] for light-emitting devices[6,7,8,9,10,11] the luminescence of which depends on the emission center used and its surrounding matrix
The transparent film formation region of the SnO-ZnO-P2O5 ternary film system was first investigated according to the preparation scheme shown in Fig. 1, while the film system itself shown in Fig. 2 along with the bulk glass formation region reported by Morena[35]
This solvent-free preparation technique resulted in a composition that is at least 40 mol% P2O5, but the region in which this amorphous film is formed differs notably from that of bulk glass prepared using conventional melt-quenching methods[35]
Summary
Recent advances in light-emitting diodes (LEDs) have been accompanied by the development of new phosphors[1,2,3,4,5] for light-emitting devices[6,7,8,9,10,11] the luminescence of which depends on the emission center used and its surrounding matrix. Monolithic inorganic (and ideally amorphous) materials possessing good emissivity will be required for industrial applications of large-area devices. A solution to this lies in the preparation of monolithic, inorganic bulk-glass phosphors containing an emission center. In order to improve the film condition, we have since focused on a solvent-free acid–base reaction that was previously used for the preparation of organic-inorganic hybrids[34] In this technique, a spontaneous reaction between Si-Cl and P-OH forms a Si-O-P network through the elimination of HCl, which suppresses foaming and produces a remarkable volume shrinkage during heat treatment. It is expected that transparent inorganic amorphous films possessing photoluminescent (PL) properties can be obtained using this solvent-free technique, and in this study is used to prepare Sn2+ -containing oxide phosphor films. By studying the luminescence properties of these films, this report provides a valuable benchmark for transparent and highly photoluminescent inorganic films produced using an industrially viable fabrication technique
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