An improvement of the thermometric performance of a single band ratiometric luminescent thermometer by the boosting of its relative sensitivity can be executed either by an increase of the probability of the excited state absorption or by the enhancement of the luminescence thermal quenching upon ground state absorption. In this article, to achieve the latter, the metal-to-metal charge transfer process has been involved. To evaluate the utility of this approach, spectroscopic properties of the KGd(WO 4 ) 2 tungstate doped with different concentrations of Tb 3+ ions were investigated in a wide temperature range. It was found that the Tb 3+ luminescence was efficiently quenched at elevated temperatures because of the metal-to-metal charge transfer process despite the large energy gap between the emitting level 5 D 4 and the level below 7 F 0 (14800 cm −1 ). The probability of the metal-to-metal charge transfer process was found to be dependent on dopant amount, and the maximal relative sensitivity as high as 1.63%/°C was obtained for an optimal 80% of Tb 3+ concentration. The use of the metal-to-metal charge transfer phenomenon and the study of the influence of the dopant ion concentration on this process is an idea that can also significantly improve single band ratiometric nanothermometers based on other optically active ions.

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Bi2ZnOB2O6 single crystal doped with Nd3+ ions is characterized by high values of nonlinear optical coefficients as well as the effective luminescence of excited Nd3+ ions, which make this system a unique candidate for near infrared to visible laser converters. The investigated Bi2ZnOB2O6:Nd3+ single crystal was grown by means of the Kyropoulos method. The vibrational properties of Bi2ZnOB2O6:Nd3+ were studied using μ-Raman spectroscopy. In particular, the Raman-active modes detected in parallel and cross-polarizations were assigned to the vibrations of the characteristic molecular groups BO3, BO4, ZnO4, and BiO6. In the absorption spectra of Bi2ZnOB2O6:Nd3+ the bands related to the optical transitions from the 4I9/2 ground state to the excited states of Nd3+ ions were detected at 432, 515, 528, 533, 577, 586, 689, 750, 810, 874, and 1605 nm. Moreover, the strong emission of Bi2ZnOB2O6:Nd3+ with a maximum at about 1062 nm (4F3/2 → 4I11/2 transition) was detected under the excitation at 514 nm. The decay kinetics profile monitored for the 4F3/2 → 4I11/2 transition of Nd3+ ions shows a relatively long fluorescence lifetime equal to 109 μs, which allows efficient emission from the 4F3/2 level of Nd3+ ions. Because of the good spectroscopic properties of the investigated system as well as nonlinear optical properties of the host, the Bi2ZnOB2O6:Nd3+ single crystal can be efficiently used as the self-frequency doubling lasers.

Specific heat, dielectric properties, domain structure, and Brillouin light scattering studies in antiferroelectric PbHf1−xSnxO3 single crystals with three different concentrations (x = 0.08, 0.1, and 0.23) are performed in function of temperature. The specific heat and dielectric data reveal clear anomalies at three temperatures denoted as T1, T2, and TC. At T1, transition from the antiferroelectric AFE1 to another antiferroelectric AFE2 phase is realized, the next phase transition (PT) is from AFE2 to an intermediate (IM) phase—at T2, and from IM to paraelectric (PE) phase at TC. PTs at T1 and T2 are definitely of the first order, whereas the PT at TC has features of the second‐order PT. The PT sequences are confirmed by changes in the domain structure. In the PE phase, Brillouin studies reveal the softening and broadening of longitudinal acoustic (LA) mode in the cooling process. The softening and broadening exhibit the maximum values near TC. The transverse acoustic (TA) mode appears near T2. Additional acoustic anomalies are also observed at T1. The temperature dependencies of LA mode indicate the existence of polar regions in PE phase and order–disorder character of the PT at TC. The other PTs are mainly of a displacive character.