Enhanced Blue Emission from Transparent Oxyfluoride Glass–Ceramics Containing Pr³⁺:BaF₂Nanocrystals

Abstract

Transparent glass–ceramics containing Pr3+:BaF2 nanocrystals in the chemical composition of SiO2–BaF2–K2CO3–La2O3–Sb2O3 oxyfluoride glass systems have been prepared from melt quenching and with a subsequent heat‐treatment method. The luminescence and structural properties of these materials have been evaluated and the results are reported. Rietveld analysis of X‐ray diffraction patterns and investigation of transmission electron microscopy confirmed the presence of BaF2 nanocrystals dispersed in the heat‐treated glass matrices. Measured UV‐Vis‐NIR absorption spectra exhibited nine bands of the transitions 3H4→3P2, (1I6, 3P1), 3P0, 1D2, 1G4, 3F3, 3F2, 3H6, and 3H5 from all the samples with nondegenerated 1I6 and 3P1 levels in the glass–ceramics. The photoluminescence spectra show an enhancement in the intensities upon ceramization, indicating the incorporation of Pr3+ ions into BaF2 nanocrystals that possess a low phonon energy (346 cm−1). This has further been corroborated from the observation of a significant threefold increase in the relative intensity ratio of blue (3P0→3H4) to red (1D2→3H4, 3P0→3H6) emissions from glass–ceramics compared with the glass. This is due to a significant decrease of multiphonon nonradiative relaxation from the 3P0 to the 1D2 level of Pr3+ in glass–ceramics. Time‐resolved spectra exhibit 3P0‐level decays faster than the 1D2 level.

Luminescence Properties of Dual Valence Eu Doped Nano-crystalline BaF2 Embedded Glass-ceramics and Observation of Eu2+ → Eu3+ Energy Transfer

“…2. As, BaF 2 has a lower refractive index compared to the precursor glass, the refractive indices of glass-ceramic samples tend to decrease with the increase in the degree of ceramization [25]. Table 1 also shows that there is a decrease in the density of samples upon ceramization.…”

“…Due to the low phonon energy sites of alkaline-earth fluoride nano-crystallites (300-400 cm −1 ), they exhibit efficient fluorescent properties with an enhanced emission efficiency and longer lifetimes because of the reduced non-radiative relaxations and possess high solubility of both sensitizer and activator rare earth ions. Recently, the photoluminescence properties of Pr 3+ doped SiO 2 -BaF 2 -K 2 CO 3 -La 2 O 3 -Sb 2 O 3 based transparent oxyfluoride glass and glass-ceramics containing BaF 2 nano-crystals have been studied by our group [25]. In this glass system, SiO 2 takes the role of glass network former while BaF 2 , K 2 O, and La 2 O 3 being network modifies and Sb 2 O 3 acts as refining agent.…”

Transparent oxyfluoride glass ceramics

“…Originally, researchers considered that rare earth activators are almost completely extracted by forming fluoride nanocrystals, i.e., distribution coefficients of rare earth ions between formed nanocrystals and their glass matrixes were very high. Moreover, R/M ratio in these fluorite-type nanophases in regard to the same R/M ratio in the initial glass (so-called segregation coefficient k) very frequently exceeds 1 (like in [41]): k is about 1.5-2.0 in [55,142,131,132]. However, de Pablos-Martin et al [25] found that for alumosilicate glasses thulium was present in both glass matrix and nanocrystalline LaF 3 .…”

“…1200 o C for germinate or borate glasses. Preparation of glass ceramics from of aluminosilicate [35-A c c e p t e d M a n u s c r i p t 6 40], silicate [41], silicoborate [42][43][44], lead-silicate [45][46][47], quartz [48][49][50][51][52][53], lead-germanate [54][55][56], tellurate-germanate [57], zinc-tellurate [58], lithiumborate, potassium-borate, barium-borate [59,60], tungsten-lead-phosphate [61] and others glasses with high metal fluoride content is thoroughly described in the literature (see Table 1). …”

Near-Infrared-to-Blue Up-conversion Luminescence in Transparent Eu3+/Yb3+ Doped Oxyfluoride Phosphors

“…In addition, the oxyfluoride matrixes combine in itself the properties of both crystal and glass that allows: extruding them, creating of large size samples, pulling the fiber, as well as carrying of ion exchange processes to produce waveguide structures. Oxyfluoride matrixes are well known for their relatively low effective phonon energy (approximately 400 cm -1 [5]) due to fluorides and the optimal size of ionic radius for doping RE phosphors that provides minimization of non-radiative losses and, as a result, more efficient UCL [6][7][8] Among other RE elements europium is considered as one of the most perspective elements for phosphors applications due to its high quantum efficiency in the orange-red range of the spectrum and, as a result, it can be used as a red phosphor for television displays, fluorescing lamps, etc. [9].…”