Device for determining the photoluminescence quantum yield and optical properties of a sample, comprising: a measuring-light source, which is configured to emit a measuring radiation, an integrating sphere, the integrating sphere comprising a first opening for the measuring radiation to radiate in, a second opening at a distance from said first opening for the measuring radiation to radiate in, and a third opening for decoupling a measured signal, a sample holder that is suitable for holding a sample in the center of the integrating sphere, a spectrally resolving detector (32, 34), the spectrally resolving detector (32, 34) being connected to the third opening, wherein a first mirror, a second mirror, and a third mirror are provided, the first mirror and the second mirror being fixed in relation to the integrating sphere and the third mirror being rotatable about an axis of rotation, and wherein the first mirror, the second mirror, and the third mirror are arranged such that the measuring radiation emitted by the measuring-light source is reflected from the third mirror to the first mirror and then from the first mirror through the first opening into the integrating sphere in a first angular position of the third mirror, and is reflected from the third mirror to the second mirror and then from the second mirror through the second opening, for directly illuminating the sample, into the integrating sphere in a second angular position of the third mirror, wherein the first mirror is arranged in relation to the axis of rotation of the third mirror and to the first opening in the integrating sphere such that the measuring radiation emitted by the measuring-light source is reflected from the third mirror via the first mirror and through the first opening into a peripheral point on the inside of the integrating sphere in the first angular position of the third mirror, the peripheral point, the center, and the first opening in the integrating sphere not being arranged on one line. a measuring-light source, which is configured to emit a measuring radiation, an integrating sphere, the integrating sphere comprising a first opening for the measuring radiation to radiate in, a second opening at a distance from said first opening for the measuring radiation to radiate in, and a third opening for decoupling a measured signal, a sample holder that is suitable for holding a sample in the center of the integrating sphere, a spectrally resolving detector (32, 34), the spectrally resolving detector (32, 34) being connected to the third opening, wherein a first mirror, a second mirror, and a third mirror are provided, the first mirror and the second mirror being fixed in relation to the integrating sphere and the third mirror being rotatable about an axis of rotation, and wherein the first mirror, the second mirror, and the third mirror are arranged such that the measuring radiation emitted by the measuring-light source is reflected from the third mirror to the first mirror and then from the first mirror through the first opening into the integrating sphere in a first angular position of the third mirror, and is reflected from the third mirror to the second mirror and then from the second mirror through the second opening, for directly illuminating the sample, into the integrating sphere in a second angular position of the third mirror, wherein the first mirror is arranged in relation to the axis of rotation of the third mirror and to the first opening in the integrating sphere such that the measuring radiation emitted by the measuring-light source is reflected from the third mirror via the first mirror and through the first opening into a peripheral point on the inside of the integrating sphere in the first angular position of the third mirror, the peripheral point, the center, and the first opening in the integrating sphere not being arranged on one line. wherein a first mirror, a second mirror, and a third mirror are provided, the first mirror and the second mirror being fixed in relation to the integrating sphere and the third mirror being rotatable about an axis of rotation, and wherein the first mirror, the second mirror, and the third mirror are arranged such that the measuring radiation emitted by the measuring-light source is reflected from the third mirror to the first mirror and then from the first mirror through the first opening into the integrating sphere in a first angular position of the third mirror, and is reflected from the third mirror to the second mirror and then from the second mirror through the second opening, for directly illuminating the sample, into the integrating sphere in a second angular position of the third mirror, wherein the first mirror is arranged in relation to the axis of rotation of the third mirror and to the first opening in the integrating sphere such that the measuring radiation emitted by the measuring-light source is reflected from the third mirror via the first mirror and through the first opening into a peripheral point on the inside of the integrating sphere in the first angular position of the third mirror, the peripheral point, the center, and the first opening in the integrating sphere not being arranged on one line.