There is a large need for a compound (phosphor) which emits light in a near infrared region, in various fields, for example, a light concentration material and a wavelength conversion material in a photovoltaic power generation device, a material for a fluorescent probe in a living body, and the like.
As an example, a photovoltaic power generation device using such a phosphor will be described. A photovoltaic power generation device (solar energy collecting window) disclosed in PTL 1 is one of known photovoltaic power generation devices that generate electrical power by causing light propagated through a light guide to be incident on a solar cell element provided at a portion of the light guide.
In this photovoltaic power generation device, a portion of sunlight incident from one principal surface of the light guide is caused to propagate through the light guide to be directed to the solar cell element. The light guide contains phosphors (fluorescent substances). The phosphor absorbs sunlight incident on the light guide and thus is excited and emits light (fluorescent light) emitted from the phosphor at this time propagates through the light guide, and is incident on the solar cell element, and thereby electrical power is generated.
In such a photovoltaic power generation device, light emitting ability of the phosphor is included as a factor of determining power production. Thus, in order to increase the power production of the photovoltaic power generation device, it is desired to use a phosphor that enables absorbing of light having a sufficiently long wavelength and has high fluorescence quantum yield. Accordingly, selection of a phosphor is important.
Here, an explanation was made as to a photovoltaic power generation device. However, similarly in other uses such as a fluorescent probe in a living body, it is very important to enable selection of a phosphor having ability of absorbing light with a sufficiently long wavelength.
As a phosphor, various substances are searched for until now. For example, a compound represented by the following expression (9)-1 (abbreviated to a “compound (9)-1”) is disclosed in NPL 1 and a compound represented by the following expression (9)-2 (abbreviated to a “compound (9)-2”) is disclosed in NPL 2.
