Phosphors have been used as wavelength converters in illumination for many years. When it is excited with blue light, the frequently used yttrium aluminium garnet doped with cerium (YAG:Ce) phosphor converts a part of blue light to a wideband yellow light, resulting in the generated light having a white color. By combining an appropriate concentration of the YAG:Ce phosphor and blue excitant light, white light of a desired correlated color temperature (CCT) can be obtained. However, this type of illumination has a lower color rendering index value (CRI). In an attempt to improve the CRI value, we mixed the YAG:Ce phosphor with europium-doped calcium sulfide phosphor (CaS:Eu), which resulted in a considerably increased CRI value. This article examines an experiment with luminescent layers consisting of a mixture of selected phosphors and polydimethylsiloxane (PDMS). Different thicknesses in these layers were achieved by changing the speed of rotation during their accumulation onto laboratory glass using the method of spin coating. The spectral characteristics of these luminescent layers as they were excited with blue light emitting diode (LED) and laser diode (LD) were then determined. A suitable combination of the YAG:Ce phosphor with a phosphor containing europium, as it was excited with a blue LED, yielded a source of white light with a CRI value of greater than 85. The response time in the tested luminescent layers to a rectangular excitant impulse (generated by a signal generator and transmitted by LD) was also measured in order to examine their potential use in visible light communications (VLC).

This publication describes the measurement of the effect of selected luminescent layer parameters on the light and communication characteristics of light generated by a luminescent layer using a light emitting diode (LED) as a radiation source. The luminescent layers were implemented based on a combination of polydimethylsiloxane (PDMS) polymer and YAG:Ce and CaS:Eu phosphors by spin coating. For the chosen weight ratios of PDMS and phosphors, a set of test samples of luminescent layers was implemented whose thicknesses differed from each other in the order of units to tens of micrometres. Experimental measurements have clearly shown that even a slightest change in the thickness of the luminescent layer has a non-negligible effect on the change of the luminous and communication parameters of the light generated by the luminescent layer. The colorimetric parameters of the colour colorimetry temperature (CCT), colour rendering index (CRI) and colour coordinates x, y (CIE 1931) were recorded for the investigated luminescent samples. The communication parameters were evaluated by measuring the error vector magnitude (EVM), modulation error ratio (MER), phase error, bit error rate (BER) and normalised signal-to-noise ratio E _b /N ₀ .

This article describes the implementation of an advanced fiber-optic intensity sensor for the comprehensive detection of axles and bogies of rail vehicles in tram transport. The sensor uses the principle of optical fiber bending, where the intensity of transmitted light is modulated due to mechanical stress on the fiber caused by the passage of a tram and the subsequent reversible deformation of the rail. The innovative design of the sensor allows for its easy installation under the rail foot, between the rail and the sleeper, replacing conventional anti-vibration pads, and includes specially designed deformable elements which the optical fiber bends and modulates the transmitted light intensity. During long-term testing (11 months in various weather conditions) conducted in the real tram depot (Ostrava, Czech Republic), 20602 tram passages were secured and analyzed. The sensor demonstrated success in detecting bogies, achieving 100% accuracy with no false positives (FPs) or false negatives (FNs). Axle detection showed an average success rate of 86.1%, with variability among different tram types up to 97.8%. The signal modulation was also subjected to detailed analysis, revealing differences in responses between various tram types, which can be attributed to differences in bogie construction and vehicle weight. Due to its electromagnetic immunity, the implemented fiber-optic sensor offers the potential for more reliable detection and broad application possibilities, including track occupancy monitoring, speed measurement, or determining the direction of travel on single-track lines. With slight optimization, the sensor could also be used to weigh rail vehicles or as an axle counter in railway or light rail transport.

This paper presents a novel fiber-optic temperature sensor based on correlated color temperature (CCT) measurement. The sensor is formed by a homogeneous mixture of polydimethylsiloxane (PDMS) and cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor, applied as a tip on the faces of an optical fiber pair. While YAG:Ce phosphors are commonly used in lighting and white light-emitting diode (WLED) technologies, their use in thermoluminescence and temperature sensing has been only minimally explored. We demonstrate that the temperature of a homogeneous PDMS–YAG:Ce mixture can be directly related to its CCT, and a highly linear dependence on temperature was identified across the studied range. The findings confirm that this CCT-based approach enables both contact and non-contact temperature measurement. The proposed optical sensors operate effectively from −60°C to 220°C (213–493 K), and their resistance to electromagnetic radiation was within a magnetic field range of −2 T to 2 T.