Thin-film Sensor Offers New Ways to Analyze Wavelengths of Light

September 14, 2022 by Chantelle Dubois

TU Dresden has developed an ultra-thin sensor the size of a strand of human hair that may open new opportunities in spectroscopy.

Researchers from TU Dresden’s Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics (IAP) have developed and patented a thin-film sensor that can perform spectroscopy at the sub-millimeter level. 

The sensor is thinner than a strand of hair at around 25µm and uses organic fluorescent emitting materials that operate at room temperature. The sensor originates from other TU Dresden spin-off technologies using organic electronics such as Senorics.


The sensor's active film

The sensor's active film is as thick as a strand of human hair, here processed on thin glass substrates. It can exhibit wavelength-dependent luminescence. Image (modified) courtesy of TU Dresden


The research team envisions this new, ultra-thin sensor creating new opportunities to use spectroscopy, including detecting counterfeit money or calibrating monochromators. 


What is Spectroscopy?

The goal of spectroscopy is to measure radiation from matter, such as light. Spectrometer devices typically consist of benchtop equipment. When the spectrometer receives radiative spectra, the device can break the spectra down into their constituent wavelengths. This breakdown forms a type of “fingerprint” that can then be used to determine what type of material is emitting radiation.


The Mechanics Behind the Sensor

The thin-film sensor contains quantum dots made from a blend of two organic materials: BP-2TA and DCJTB.

These quantum dots contain what are called “singlet” and “triplet” emitters. Singlet emitters are fluorescent, providing a brief glow in reaction to excitation from a light source. The triplet emitters are phosphorescent and will have a brief afterglow in reaction to excitation from a light source. 


A diagram showing the (a) layout of the sensor and (b) detected transients

A diagram showing the (a) layout of the sensor and (b) detected transients. Image used courtesy of Advanced Materials


The intensity of the combined fluorescent and phosphorescent glow is what can be used to infer the wavelength of light.

In experiments, the research team used a monochromator to emit wavelengths between 300nm and 410nm. The experiments were performed at room temperature using a nitrogen atmosphere to eliminate interference from oxygen. The team determined that the thin-film sensor could discriminate wavelengths in increments of 1nm.


The experimental setup

The experimental setup. Image used courtesy of Advanced Materials


How the Prototype May Benefit Anti-Counterfeit Applications

One possible application of this thin-film spectrometer is to measure luminescence for anti-counterfeiting

Counterfeiting is an issue in many industries, including medicine, retail, electronics, and finance. Companies across these industries are investigating how to create anti-counterfeit labels that can verify the authenticity of different products. These methods must be verified easily by a layperson.

With this new research, consumer-grade counterfeit label scanners may be manufactured to luminesce at specific intensities. A sensor, such as the one from TU Dresden, could possibly be integrated into IoT devices such as a smartphone to detect this luminescence and indicate whether the product is authentic or not. 


How TU Dresden's Spectrometers Sizes Up to Others

How does TU Dresden's prototype compare to other spectrometers available? Consumer-grade, hand-held spectrometers have a range of approximately 200nm to 700nm with a resolution of around 5nm. More expensive, research-quality spectrometers have a range of 100nm to 1100nm with resolutions less than 0.5nm.

While TU Dresden’s new film sensor’s sensing range is a bit narrower, its resolution is still an improvement on many consumer-grade devices.