Résumé: Er3+-doped BaF2 single crystals were investigated with two primary aims: first, to probe the infrared emissions from the 4I11/2 level (around 1.0 μm) under 1500-nm excitation and, second, to use the crystal to enhance the efficiency of silicon-based solar cells through upconversion mechanism. Upon excitation at 1500 nm, the upconversion emission spectrum of the Er3+-doped BaF2 single crystals, recorded in the range of 480–1080 nm, exhibited two well-structured visible bands at 538 and 650 nm, along with a strong near infrared emission at 971 nm. This strong 971-nm emission has an emission cross-section of approximately 0.23 × 10−20 cm2. As with any phenomenon inherent to energy transfer by upconversion, the 4I11/2 fluorescence decay exhibits a rise time followed by a long decay of approximately 15 ms and a positive optical gain from the low values of the population inversion coefficient, which could potentially give rise to laser emission from this level. When we place our crystal on a photovoltaic device illuminated by 1500-nm wavelength radiation, we record a photocurrent of 300 μA at an illumination power of 85 mW. This indicates that the Er3+-doped BaF2 crystal is highly suitable for significantly enhancing the efficiency of silicon-based solar cells.

Résumé: The luminescence properties of erbium and yttrium co-doped cadmium difluoride with three different concentrations of yttrium were investigated. First, we synthesized single crystal samples with good optical quality using the Bridgman technique. From the optical absorption spectra, recorded at room temperature, both in the ultraviolet–visible and infrared spectral ranges, Judd–Ofelt analysis was performed based on yttrium concentrations to predict the radiative properties of Er3+ luminescent ions. For the 10% optimum concentration of yttrium, a detailed photoluminescence investigation was carried out. We mainly explored green, red, and near-infrared fluorescence under different excitation wavelengths and presented their highlight spectroscopic characteristics. The desired transitions had relatively high emission cross-sections both under visible and near-infrared excitation. Optical gain followed a similar trend. Furthermore, the dynamic fluorescence study showed a significant increase in the measured lifetime under an 800 nm infrared excitation. The upconversion process under an 800 nm excitation produced quantum efficiency greater than 100% due to the contribution of more than one energy transfer mechanism.

Résumé: Absorption, excitation, fluorescence and decay spectra are carried out at room temperature on Er3+ (1%), Yb3+ (4%): Cd.7Sr.3F2 mixed single crystals. These crystals, with a good optical quality, are grown by the standard Bridgman method. This work concerns mainly the spectroscopic properties of the Er3+ ions incorporated in a fluorite-type crystal. Using the room temperature absorption spectra, the standard Judd–Ofelt (JO) model is applied to absorption intensities of Er3+ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are in accordance with those of other fluoride hosts with good root mean square fitting. Compared to oxide materials, fluoride materials have, in general, low values ​​of Ω2. The low value of Ω2 is correlated to the cubic nature of the site occupied by the rare earth in the host matrix. These JO intensity parameters are then applied to determine the radiative transition probabilities (AJJ′), radiative lifetimes (τrad) and branching ratios (βJJ′) of Er3+ transitions. The green emission generated by the Er3+ ions directly excited in UV level, consisting in three well-resolved major lines, is more intense than the one. We have measured the fluorescence lifetime, the cross-section emission, the gain and the radiative quantum efficiency for both green and red band emissions. The obtained results are in good agreement with those of other fluoride laser crystals. From, the obtained spectroscopic data we suggest that Cd.7Sr.3F2 may offer green and red visible laser emission when doped with Er3+ ions.

Résumé: Rare earth doped sub-micrometric luminescent materials are promising candidates for temperature sensing and play an efficient role in many technological fields. In this paper, a new optical sensor is developed for measuring local temperatures. This sensor is based on a thermal-resistive probe and on photoluminescence of a luminescent fluoride microcrystal. The final purpose is to develop a device calibrated in temperature and capable of acquiring images of local temperature at sub-micrometric scale. Indeed, the sensor temperature can be obtained in two distinct ways: one from the thermal probe parameters and the other from the green photoluminescence generated in the anti-Stokes mode by the active Er ions directly excited by a red laser. The thermal probe is based on Wollaston wire whose thermal-resistive element is in platinum/rhodium. Its temperature is estimated from the probe electrical characteristics and a modeling. A microcrystal of Sr0.3Cd0.7F2: Er3+(4%)–Yb3+(6%) of about 25 μm in diameter is glued at the probe extremity. This luminescent material has the particularity to give a green emission spectrum with intensities sensitive to small temperature variations. Using the fluorescence intensity ratio (FIR) technique, the crystal temperature is estimated from the intensity measurements at green wavelengths 522, 540 and 549 nm by taking advantage of particular optical properties due to the crystalline nature of Sr0.3Cd0.7F2: Er3+−Yb3+. The microcrystal temperature is then assessed as a function of electric current in the thermal probe by applying the Boltzmann’s equations. The coupling of the scanning thermal microscope (SThM) with the photoluminescence probe reveals that the particle fluorescence signal is affected by the temperature rise of an electrical microsystem submitted to a Joule heating. The first results are presented and discussed.

Résumé: Single crystals of Er3+:CdF2 with good optical quality were grown by a Bridgman technique after purification of the starting materials. Absorption and emission spectra are recorded at room temperature. The Judd–Ofelt (JO) analysis was applied to obtain the three phenomenological intensity parameters and the transition strengths. These JO parameters are used to calculate the radiative transition probabilities, the radiation lifetimes and the branching ratios. The results obtained are in good agreement with those of other fluoride laser materials. We also carried out luminescence measurements for red and green emission. The studied host may offer infrared and visible laser emissions.