Abstract
The mesoporous nanocrystal powders BaF2 and CaF2 with a specific surface up to 34.8 and 88.7 sq.m/g, respectively, are produced by the pulsed electron beam evaporation method in vacuum. The influence of thermal annealing of nanoparticles on air in the range of temperature from 200 to 900°C on the size, morphology of particles and change of their magnetic and luminescent properties investigated have been investigared. The essential stoichiometric impurity (overage of metals) and significant growth in a specific surface of nanopowders (NP) BaF2 and CaF2 after annealing at the temperature of 200°C have been detected. It is established that the synthesized NP BaF2 is a paramagnetic while initial material in the bulk state is diamagnetic. After annealing at 900°C appears the small ferromagnetic contribution at NP BaF2. Produced NP CaF2 showed ferromagnetic behavior. In literature there is no information about the ferromagnetism of CaF2. Appearance of the ferromagnetic response can be explained with formation of structural and radiation defects (F-centers, etc.). The analysis of PCL and magnetization curves of samples BaF2 and CaF2 allows drawing conclusions about their connection.
Highlights
Nanofluorides of alkali earth metals have good prospects for use as catalysts and photonics materials, including precursors of optical ceramics and materials for biomedical applications [1]
Significant growth in the specific area of the CaF2 and BaF2 NPs was found after annealing at the temperature of 200o C (Table 1)
This study found the growth of the NP CaF2 and BaF2 specific surface after annealing at a temperature of 200°C and an increase in the intensity of the red strip NP BaF2 by 2.1 times after annealing, due to an increase in the number of the F-centers of the 1st type in ~3 and of the 2nd type in ~4.3 times and change of Pulse cathode luminescence (PCL) spectrum of CaF2 NP
Summary
Nanofluorides of alkali earth metals have good prospects for use as catalysts and photonics materials, including precursors of optical ceramics and materials for biomedical applications [1]. Various methods for preparing CaF2 nanoparticles are known, the first being chemical ones: the exposure of corresponding nanoscale oxides to gaseous hydrogen fluoride [2], chemical precipitation from solutions [3, 4], co-precipitation from acidic solutions of corresponding salts using a hydrogen fluoride solution with product crystallization in cubic syngony [5], thermolysis of alkali earth trifluoroacetates [6, 7] and others.
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