Reference measurement

A method for determining a decay time of a luminescence of a sample, comprising the following steps:

• exciting a light source by means of an excitation current of a current source, wherein the magnitude of the excitation current of the current source is periodically changed with frequency f between a minimum magnitude and a maximum magnitude;
• irradiating the sample with a light of a wavelength suitable for exciting luminescence in the sample, wherein the irradiation intensity is varied periodically with frequency f over several periods;
• measuring a light emitted from the sample in a receiver, generating a first electrical signal as a function of the light emitted from the sample, and amplifying the first electrical signal, wherein the light emitted from the sample varies in intensity periodically with frequency f such that the first electrical signal varies as a function of frequency f;
• detecting a first phase difference dF1 between the excitation current and the amplified first electrical signal;
• generating a second electrical signal with frequency f for determining the additional phase shift caused by the measurement and amplification, wherein the second electrical signal is generated directly from the excitation current of the current source without an interposition of a light source and is subsequently amplified, wherein the sample is not irradiated during this time;
• detecting a second phase difference dF2 between the excitation current and the amplified second electrical signal;
• and
• determining the decay time of the luminescence of the sample based on a phase difference dF between the excitation current and the light emission of the sample, wherein the phase difference dF is determined from the difference of the first and second phase differences of the amplified electrical signals:
• dF=dF1−dF2.