Title: Efficient luminescent materials for multifunctional NIR phosphor-converted LEDs
Research proposal No: 1.1.1.9/LZP/1/24/046
Duration: 01.07.2025.-30.06.2028.
Project Leader: Ph.D. Meldra Ķemere
Total budget: 184 140 EUR
European Regional Development Fund (ERDF) funding: 156 519 EUR
ISSP UL budget: 9 207 EUR
Project description:
Near-infrared (NIR) radiation has applications in medicine, anti-counterfeiting, night vision, non-destructive food analysis, etc. Lately, near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) have shown great potential as NIR sources, however, they still possess significant drawbacks – relatively low quantum efficiency and poor thermal stability. The project aims to develop novel thermally stable Cr3+-doped NIR phosphors emitting in the 750-950 nm spectral range. Materials with a garnet-type structure A3B2C3O12 doped with Cr3+ ions will be studied in a broad temperature range using advanced structure characterisation and spectroscopy techniques. Gd3Ga5O12 is chosen as the starting material to be optimised using crystal field engineering methods. As a result of project implementation, novel NIR phosphors with enhanced luminescence properties will be elaborated and reported in at least 3 scientific articles in Q1/Q2 journals and in 4 conferences; the practical applications will be demonstrated in a NIR pc-LED prototype and submission of a patent application. This research project will contribute to the Smart Specialisation Strategy (RIS3) area “Smart materials, technologies and engineering systems”, by developing efficient optical materials and advancing novel products via future applied project calls. The project will be implemented at the Institute of Solid State Physics (ISSP UL).
PROJECT PROGRESS
Time period: 01.11.2026. - 30.04.2026.
1. Synthesis, optimisation, and structural characterisation of materials (WP1)
A complete sample series was synthesized at the Institute of Solid State Physics, University of Latvia, in which ZnO/ZrO2 was added to the Gd3Ga5O12 series, with the composition Gd3Ga5‑2xZnxZrxO12:0.05Cr, where x = 0–1 (a total of 8 samples).
To investigate in greater detail the dependence of luminescence intensity on chromium concentration, the sample with x = 0.2 ZnO/ZrO2 was selected (based on spectroscopy measurements within WP2 and WP3). The synthesis of the series with the composition Gd3Ga4.6Zn0.2Zr0.2O12:xCr was started, and 3 samples were synthesized, where x = 0.025, 0.05, 0.075. The structure and phase purity of the samples were confirmed by X-ray diffraction (XRD) measurements.
2. Characterisation of spectroscopic properties (WP2)
The characterization of the spectroscopic properties of the prepared sample series was continued. Luminescence measurements at low temperatures (10 K) were performed for selected samples. During the mobility visit in Poland, luminescence and quantum yield measurements were carried out for selected samples.
In the luminescence spectra, with increasing x (ZnO/ZrO2) concentration in the samples, a red shift of the Cr3+ luminescence band was observed, with the band maximum shifting from 732 nm to 804 nm and the full width at half maximum increasing from 102 nm to 179 nm. A decrease in the decay time was also observed. With increasing x (ZnO/ZrO2) concentration in the samples, the maximum luminescence intensity decreases (for the x = 1 sample, 36% of the intensity of the x = 0 sample remains), while the integrated band intensity, taking into account the increase in the full width at half maximum, reaches 65% of the intensity of the x = 0 sample.
Mobility visit to the branches of the “Lukasiewicz Research Network” Institute of Microelectronics and Photonics in Warsaw and Kraków (within WP2)
A mobility visit was performed from November 12 to November 22, 2025, in Warsaw and Kraków, Poland, in the Smart Materials Research Group under the supervision of Ph.D. Kamila Leśniewska-Matys, Wolczynska 133, Warsaw (12–19.11), and in the LTCC Technology Research Group under the supervision of Dr. Krzysztof Szostak, Zablocie 39, Kraków (11–22.11).
During the mobility visit, luminescence and quantum yield measurements in the NIR spectral region were performed for selected samples, since quantum yield measurements in the NIR spectral region are not available at the Laboratory of Spectroscopy at ISSP UL. The quantum yield values reached 75%. Sample synthesis methodology, measurement methodology, possibilities for future collaboration, and the Polish partner’s experience in cooperation with industry were discussed.
3. Analysis of the thermal stability of NIR luminescence
The investigation of the dependence of sample luminescence intensity on temperature was started by heating the samples from room temperature up to 200 °C.
4. Analysis and dissemination of results (WP5)
On April 1, 2026, participation took place in the event “Shadow Day” at the Laboratory of Spectroscopy, Institute of Solid State Physics, University of Latvia, where four students from grades 7–9 were introduced to the work of a researcher, research laboratories, scientific projects, spectroscopy measurements, different types of luminescence, and laboratory equipment.
Time period: 01.07.2025. – 31.10.2025.
1. Synthesis, optimisation, and structural characterisation of materials (WP1)
At the Institute of Solid State Physics, University of Latvia, we worked on optimizing the synthesis conditions for our samples and prepared several series:
Gd3Ga5O12:0.05Cr – initial synthesis conditions optimized (6 hours at 1300 °C, using 1 wt% boric acid as a flux)
Gd3Ga5-2xMgxZrxO12:0.05Cr, where x = 0–1 (9 samples)
Gd3Ga5-2xZnxZrxO12:0.05Cr, where x = 0–1 (4 samples)
The structure and purity of all samples were confirmed with X-ray diffraction (XRD).
2. Characterisation of spectroscopic properties (WP2)
The studies of the optical properties of the samples were started. Initial measurements at room temperature included: diffuse reflectance, luminescence spectra, excitation spectra, and luminescence decay kinetics. Some measurements were also performed during a visit in Vilnius, Lithuania.
We observed that increasing Mg/Zr or Zn/Zr concentrations in the samples shifted the Cr³⁺ emission to longer wavelengths and affected the emission intensity, width of the luminescence bands, and decay time. These results will be analysed further in details.
3. Mobility to the Institute of Chemistry, Vilnius University, Lithuania (within the framework of WP1)
From 6 to 23 October 2025, a mobility visit took place at the Institute of Chemistry, Vilnius University, in the Sol-Gel Chemistry Group, supervised by Professor Aleksej Žarkov. I visited labs at the Faculty of Chemistry and Geosciences and the Center for Physical and Technological Sciences.
During the visit, different synthesis methods for garnet materials and their use in the project were discussed. Luminescence spectra and decay measurements were carried out using an Edinburgh Instruments FLS 980 spectrometer, which offers capabilities currently unavailable at the Institute of Solid State Physics, University of Latvia. This experience will be useful for future studies. Results were analysed, and perspectives for further collaboration were discussed.
4. Analysis and dissemination of the results (WP5)
On 26 September 2025, I participated in the “Researchers’ Night” event at the Institute of Solid State Physics, University of Latvia. I shared with visitors how luminescent materials emit light in different spectral ranges and their potential applications in everyday life and technology.