The system includes a spectrometer, integrating sphere with a calibrated radiation source, laser light source, optical fibers, and accompanying fixtures. The LiSen Optics spectrometer has a high signal-to-noise ratio, low stray light, and a broad dynamic range, making it suitable for measuring different wavelengths and intensities of excitation and emission light. The system also includes powerful, dedicated testing software, which is simple to use and facilitates quick and convenient testing processes.

The iSpecRad-PQY system supports the measurement of powder, thin film, and liquid samples, and is applicable in fields such as organometallic complexes, fluorescent probes, dye-sensitized PV materials, OLED materials, LED phosphors, etc.

Basic Principle

The absorption and emission energy diagram for fluorescence and phosphorescence

The energy diagram for fluorescence and phosphorescence absorption and emission processes describes the electronic energy levels of typical organic molecules and the electronic transitions between these levels. S0, S1, and T1 represent the ground state, lowest singlet, and lowest triplet states, respectively. After photoexcitation, excited-state molecules can return to the ground state through various radiative (involving light emission, like fluorescence and phosphorescence) and non-radiative (internal conversion and intersystem crossing) processes. Radiative and non-radiative processes compete with each other.

The absorption and emission energy diagram for fluorescence and phosphorescence explains the process of electron transitions in ordinary organic molecules. The energy levels S0, S1, and T1 represent the ground state, the lowest singlet state, and the lowest triplet state, respectively. After photoexcitation, excited-state molecules can return to the ground state via several transition paths, including radiative processes (like fluorescence and phosphorescence) and non-radiative processes (internal conversion and intersystem crossing). These radiative and non-radiative processes compete with each other.

Photoluminescence (PL) refers to the phenomenon where a material absorbs photons (or electromagnetic waves) and re-emits photons. This process includes both fluorescence and phosphorescence emissions. Quantum mechanically, this process can be described as the material absorbing a photon to transition to a higher excited state and then returning to a lower energy state, emitting a photon in the process. Photoluminescence is one form of fluorescence.

In current research on photoluminescent materials, the calculation of fluorescence quantum efficiency is crucial as it reflects the light-emitting capability of the materials. Fluorescence quantum efficiency, also known as quantum yield of fluorescence or fluorescence efficiency, is an important characteristic. Typically, the quantum yield is calculated by first exposing a blank container to the excitation light to obtain the total photon count. Then, a sample is placed in the container and exposed to the excitation light to determine the number of unabsorbed photons and emitted photons. The absolute Photoluminescence Quantum Yield (PLQY) is calculated by the ratio of emitted photons (in the green area)

to absorbed photons (in the blue area) per unit time (second), expressed as:

Photoluminescence

There are two methods to measure the quantum yield of a sample

1.Relative Quantum Yield Measurement: Requires a standard material with a known quantum yield for reference. The quantum yield of the sample is calculated by comparing the absorbance and fluorescence of the standard material and the sample. This method is only applicable to liquid samples.

2.Absolute Quantum Yield Measurement: Does not require a standard sample for comparison and is broadly applicable to liquids, films, and powder samples. This method involves using an integrating sphere accessory; the inner surface of the integrating sphere is generally coated with highly reflective materials like barium sulfate or polytetrafluoroethylene (PTFE). The excitation light or emitted light from all directions of the sample surface is homogenized by the integrating sphere before exiting and being detected by a spectrometer.

Method for Testing Absolute Fluorescence Quantum Yield

Typical Applications

● Inorganic and organic photoluminescence

● Measurement of organometallic complexes and coordination compound compounds

● Dye-sensitized PV materials, OLED materials

● Quantum efficiency measurement of LED and organic EL phosphors

● Quantum efficiency measurement of film samples for transmission fluorescence/reflection fluorescence (non-contact fluorescent phosphor samples, etc.)

● Fluorescence measurement of Quantum Dots, fluorescent probes (probes), biomaterials, encapsulation compounds, etc.

● Quantum efficiency measurement of dye-sensitized solar cells

Accessories