Low-field Sites Research Articles

Survival and growth of triploid eastern oysters, Crassostrea virginica, produced from wild diploids collected from low-salinity areas

Triploid Eastern oysters have been reported to suffer greater mortalities than diploids when exposed to low-salinity (<5) conditions in the U.S. Gulf of Mexico and Atlantic estuaries. As such, the effect of broodstock parentage was investigated on the low-salinity tolerance of triploid progeny produced by mating diploid females (collected from three Louisiana estuaries differing in salinity regimes) with male tetraploids at two hatcheries. Diploid crosses were also produced using the wild broodstocks to verify expected differences in low-salinity tolerance among diploid progeny and between ploidy levels. All progeny were deployed at low and moderate-salinity (averages of 9.3 and 19.4) field sites to monitor monthly growth and mortality. Sex ratio, gametogenic stage, gonad-to-body ratio, condition index, and Perkinsus marinus infection were also measured periodically at both field sites Although high triploid mortality at the low-salinity site prevented complete analysis, results indicated that diploid parentage had little effect on triploid survival at low salinity. Broodstock parentage affected diploid mortality and growth, although results did not match with predictions made based on historical salinity at broodstock collection sites. Ploidy level had the largest effect on triploid survival and growth followed by the hatchery site where the oysters were produced.

Impact of Cr3+ substitution on the nephelauxetic ratio and Racah parameter of Cr-Mn-Zn nanoferrites

For the first time, we present the ligand field splitting (10Dq) nephelauxetic ratio (β), Racah parameter (B) and stability of Cr3+ within Mn–Zn nanoferrite which synthesized using the citrate route. These parameters were determined via optical absorption spectra. The obtained bands in the significance range of optical absorption spectra are wide as well as asymmetric; therefore the deconvolution process becomes a necessary task. The values of 10Dq and B have been estimated from the produced bands. The values of 10Dq are observed to increase from 16366.61 to 16447.37 cm−1 whereas, B values are observed to decrease from 829.81 to 760.80 cm−1 with additional Cr3+ substitution. The increasing 10Dq and decreasing B values, evidence for bonds between Cr3+ ions with their environments became a further covalent (less ionic). Moreover, the values of β are observed to decrease for further Cr3+ substitution. This decrease of β produces less stability between Cr3+ and its ligand. Furthermore, Dq/B values declare that Cr3+ centers are in the low-field sites by a slight tendency towards the high-field sites with further Cr/Fe substitution process. Therefore, it was suggested that Cr3+ substituted Mn–Zn nanoferrites are excellent candidates for diverse optical applications such as a tunable laser.

DEVELOPMENT OF SCLEROTINIA IN NARROWLEAF (Lupinus angusti-folius L.) AND WHITE (Lupinus albus L.) LUPIN SINGLE AND MIXED CROPS UNDER DIFFERENT WEATHER CONDITIONS IN BRYANSK REGION

White rot caused by ascomycetous fungus Sclerotinia sclerotiorum (Lib.)de Bary. is a widely spread disease of many cultivated and wild plants. In the Non Chernozem zone of Russia the epiphytotic development of white rot in white and narrowleaf lupin crops began in 2008 and is related to climate change towards warming. The article presents the first report on dependence between weather conditions in the Non Chernozem zone and white rot infection of white and narrowleaf lupines in single and mixed crops. High significant correlation coefficients have been obtained between air moisture and pods’ white rot infection of the narrowleaf lupin in June (r = 0.95, р = 0.001), and of the white lupin in June and July (r = 0.90, р = 0.006; r = 0.81, р = 0.026, respectively). High significant negative correlation coefficients between narrowleaf and white lupin yields in single and mixed crops and Sclerotinia infection of pods have been revealed (r = -0.92, р = 0.003 and r = -1.00, р = 0.002, respectively; r = -0.97, р = 0.000 and r = -0.88, р = 0.122, respectively). The lupin species differed in susceptibility to the pathogen. This work aimed to evaluate the white rot development and harmfulness in white and narrowleaf lupin crops depending on weather of the vegetation season and crop type under the conditions of Bryansk region. The narrowleaf lupin var. Belozernyi 110 and the white lupin var. Dega were cultivated in single crops and in mixed crops with spring wheat var. Iren in 2008-2012, 2014, and 2016 in the North-East of Bryansk region (an experimental field of All-Russian Lupin Scientific Research Institute). Climatic data were received from the meteorological station on the territory of the institute. Lupin plants were infected with white rot mycelium by the wet chamber method. Plants infection was evaluated during the vegetation period (stem and bud formation, flowering and pods’ formation stages). The yield of each plot was weighted after the total threshing (a combine-harvester Sampo-500, Sampo Rosenlew, Finland). Intensive pathogen development on the tested lupin species in single and mixed crops was in rainy and warm June-August, at 66.2-80.3 % air moisture. Under rainy, warm and windy conditions white rot spread among plants in lupin crops both by ascospores and by mycelium particles. The first lesion focuses appeared on stems in low field sites and in dense crops. Depressive disease development occurred at air moisture from 54.1 to 60.3 %. White lupin plants were more susceptible to the disease, probably due to the morphological peculiarities of this species. Under favorable conditions for the disease, the incidence of pod infection averaged 15.3-34.8 % in white lupin single crops and 8.4-34.7 % in narrowleaf lupin single crops. Herewith seed yield losses made 14.3-39.2 % and 3.0-34.7 %, respectively. Under dry conditions of 2010, the white lupin infection incidence was 0.3 % in mixed crops with no infection of the narrowleaf lupin observed. The infection of the narrowleaf and white lupins in their single crops made 0.1 and 1.3 %, respectively. The white rot was more harmful for lupin crops upon a combination of sufficient or excessive moisture and optimal temperature in the second part of vegetation. During this period, the pods were formed on the main and lateral stems, and the plant foliation was maximum too. The latter creates favorable conditions for the pathogen inside the crops. Pod infection in lupines decreased significantly in mixed lupin-and-cereal crops, 1.4-1.6-fold for the white lupin, and 1.3-2.3-fold for the narrowleaf lupin. Obviously, the lupin-and-cereal mixed crops create the conditions which are less favorable for the pathogen development and spread, therefore decrease infection of lupin plants and pods.

Soil legacy determines arbuscular mycorrhizal spore bank and plant performance in the low Arctic

Human impact is rapidly changing vegetation globally. The effect of plant cover that no longer exists in a site may still affect the development of future vegetation. We focused on a little studied factor—arbuscular mycorrhizal (AM) fungus spore bank—and its effect on three test plant species. In a low Arctic field site, plots were maintained for 6 years, devoid of any vegetation or with a Solidago virgaurea monoculture cover. We analysed the AM fungal morphospecies composition and identified 21 morphospecies in the field plots. The AM morphospecies community was dominated by members of Acaulosporaceae. Monoculturing under low Arctic field conditions changed the soil AM spore community, which became dominated by Glomus hoi. We tested the soil feedback in the greenhouse and grew Solidago virgaurea, Potentilla crantzii and Anthoxanthum odoratum in the field soils from the plots without plant cover, covered with Solidago virgaurea or with intact vegetation. Our results suggest that monoculturing resulted in improved N acquisition by the monocultured plant species Solidago virgaurea which may be related to the AM fungus community. Our results show that a rich community of AM fungus spores may remain viable under field conditions for 6 years in the low Arctic. Spore longevity in field soil in the absence of any host plants differed among AM fungus species. We suggest that AM fungus spore longevity be considered an AM fungal life-history trait.

Nitrogen use efficiency and productivity of first year switchgrass and big bluestem from low to high soil nitrogen

Despite an abundance of research on the biomass response to nitrogen fertilizer in established switchgrass fields, there is a dearth of knowledge of the first year response in switchgrass, and nothing yet available for big bluestem. Based on differences in their C4 photosynthetic subtypes, big bluestem may show greater photosynthetic (PNUE) and above-ground whole plant nitrogen use efficiency (NUE) over switchgrass. Here we report the first year biomass response to nitrogen fertilizer for two cultivars of upland switchgrass and three cultivars of big bluestem. We first performed a greenhouse experiment with four nitrogen treatments ranging from 1.5 dmol m−3 to 16 mol m−3 aqueous nitrogen solutions. Here we measured PNUE mid-way through the experiment and harvested plants green to measure above-ground whole plant NUE. We also compared these cultivars at two field sites with contrasting soil nitrogen content. At low soil nitrogen, big bluestem “Prairie View” achieved both the highest NUE in the greenhouse and greatest biomass in the field. Switchgrass produced significantly more biomass than big bluestem at the high nitrogen field site, whereas biomass production was similar for both species at the low nitrogen field site. Although both species responded positively to increasing soil nitrogen, switchgrass did increasingly more so compared to big bluestem, with a 20% greater biomass stimulation in the greenhouse from low to high soil nitrogen. Net CO2 assimilation rates showed a similar response with biomass production to the nitrogen treatments, allowing switchgrass “Sunburst” to achieve a slightly greater PNUE compared to big bluestem “Prairie View”.

Physical and spectroscopic studies of Cr3+ doped mixed alkaline earth oxide borate glasses

A series of mixed alkaline earth oxide glasses xMgO-(30-x)BaO-69.8B2O3-0.2Cr2O3 were prepared and studied using electron paramagnetic resonance (EPR), optical absorption, Raman spectroscopy and photoluminescence experimental techniques. The optical absorption spectra revealed the characteristic octahedral symmetry of Cr3+ions through three broad band transitions 4A2g(F)→ 4T2g(F), 4A2g(F)→ 4T1g(F), and 4A2g(F)→ 2T1g(P). The crystal field (Dq) and Racah parameters (B and C), the optical band gap and Urbach energies of the glass samples were also reported along with the physical properties like density and molar volume. In the EPR spectra three resonance signals corresponding to Cr3+ ions were observed. A broad signal with g = 5.110 was observed which belongs to the isolated Cr3+ centers localized in the strongly distorted octahedral (rhombic) sites of the glass network, a narrow signal (g = 1.960) corresponding to the Cr3+ centers in the weekly distorted (cubic) sites of the glass network, and a third very broad signal (g = 2.210) was also observed corresponding to Cr3+- Cr3+ paired centers coupled by magnetic dipolar interaction. Another resonance signal with effective value g ≈ 4.220 was attributed to Fe3+ ions impurity. The number of spins (N) participating in the resonance and susceptibility (χ) values at room temperature were reported and their values varied in a non-linear manner with the composition exhibiting mixed oxide effect. The estimated molecular bonding coefficients (α) values indicated stronger ionic contribution. The Raman spectral investigations were carried out. The Photoluminescence spectra bands near 690 and 750 nm correspond to the Cr3+ centers in high and low field sites respectively.

Low and high field sites of Cr3+ ions in calcium tetraborate glasses

This paper presents electron paramagnetic resonance and detailed optical spectroscopic characterization of CaB4O7 glasses doped with Cr3+. The luminescence excitation spectrum consists of two broad bands related to transitions from the ground state 4A2g to the excited states 4T1g and 4T2g of the octahedrally coordinated Cr3+ ions. The photoluminescence spectrum is a superposition of the R line related to the 2Eg→4A2g transition and broad band related to the 4T2g→4A2g transition. The analysis of electron paramagnetic resonance spectra allowed to distinguish different Cr3+ sites, whereas the analysis of luminescence and luminescence excitation spectra allowed to characterize the crystal field distribution in the glass host.

Synthesis, EPR and optical spectroscopy of the Cr-doped tetraborate glasses

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence spectra as well as luminescence kinetics of the Li2B4O7:Cr and KLiB4O7:Cr tetraborate glasses were investigated at T=300K. The Li2B4O7:Cr and KLiB4O7:Cr glasses containing 0.4 and 1.6mol.% Cr2O3 of high optical quality were obtained from polycrystalline compounds by fast cooling of the melts. The X-band EPR spectroscopy shows that the Cr impurity is incorporated in the tetraborate glass network as isolated Cr3+ centers and Cr3+–Cr3+ pairs coupled by magnetic dipolar and exchange interactions. The EPR spectral parameters (geff and ΔBpp) of both Cr3+ and Cr3+–Cr3+ centers in the Li2B4O7:Cr and KLiB4O7:Cr glasses were measured and analyzed. All transitions in optical absorption, luminescence excitation and emission spectra of these glasses are identified. Broad complex bands that peak near 615, 405, and 350nm in optical absorption and luminescence excitation spectra correspond to the 4A2g(F)→4T2g(F), 4A2g(F)→4T1g(F), and 4A2g(F)→4T1g(P) spin-allowed transitions of the Cr3+ centers in distorted octahedral sites of the tetraborate glass network. The octahedral (cubic) crystal field strength (10Dq) and Racach parameters (B and C) for Cr3+ centers in Li2B4O7:Cr and KLiB4O7:Cr glasses are estimated. Narrow and broad emission bands in red – NIR regions are assigned to the 2Eg(F)→4A2g(F) (R1 line) and 4T2g(F)→4A2g(F) (electron-vibration) transitions, which correspond to the Cr3+ centers in high-field and low-field sites, respectively. All observed emission bands are characterized by non-exponential decay. Measured average lifetimes and local structure of the Cr3+ centers in high-field and low-field sites of the Li2B4O7:Cr and KLiB4O7:Cr glass network have been discussed.

Magnetic Coulomb Fields of Monopoles in Spin Ice and Their Signatures in the Internal Field Distribution

Fractionalization-the breaking up of an apparently indivisible microscopic degree of freedom-is one of the most counterintuitive phenomena in many-body physics. Here we study its most fundamental manifestation in spin ice, the only known fractionalized magnetic compound in 3D: we directly visualize the 1/r(2) magnetic Coulomb field of monopoles that emerge as the atomic magnetic dipoles fractionalize. We analyze the internal magnetic field distribution, relevant for local experimental probes. In particular, we present new zero-field NMR measurements that exhibit excellent agreement with the calculated line shapes, noting that this experimental technique can in principle measure directly the monopole density in spin ice. The distribution of field strengths is captured by a simple analytical form that exhibits a low density of low-field sites-in apparent disagreement with reported muon spin rotation results. Counterintuitively, the density of low-field locations decreases as the local ferromagnetic correlations imposed by the ice rules weaken.

Growth, Structure, and Optical Properties of the Cr3+:K0.6(Mg0.3Sc0.7)2(MoO4)3 Crystal

The Cr3+-doped K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal was grown from a flux of K2Mo3O10 by the top seeded solution growth method. The K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal crystallizes in the rhombohedral system in space group R3c̅. The K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal has a highly disordered structure. Investigation of the spectral properties of the Cr3+:K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal shows that it exhibits broad absorption and emission bands, which are caused by the disordered structure of the K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal, except for the broad emission of Cr3+ ions. On the basis of the absorption and emission spectra, the crystal field strength Dq/B and Racah parameter C have been calculated. The Dq/B value of 2.18 implies that Cr3+ ion occupies the low crystal field site in the Cr3+:K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal. These results suggest that the Cr3+:K0.6(Mg0.3Sc0.7)2(MoO4)3 crystal is a potential tunable laser crystal material.

Assessment of the consistency of H 2O line intensities over the near-infrared using sun-pointing ground-based Fourier transform spectroscopy

We report on the consistency of water vapour line intensities in selected spectral regions between 800–12,000 cm −1 under atmospheric conditions using sun-pointing Fourier transform infrared spectroscopy. Measurements were made across a number of days at both a low and high altitude field site, sampling a relatively moist and relatively dry atmosphere. Our data suggests that across most of the 800–12,000 cm −1 spectral region water vapour line intensities in recent spectral line databases are generally consistent with what was observed. However, we find that HITRAN-2008 water vapour line intensities are systematically lower by up to 20% in the 8000–9200 cm −1 spectral interval relative to other spectral regions. This discrepancy is essentially removed when two new linelists (UCL08, a compilation of linelists and ab-initio calculations, and one based on recent laboratory measurements by Oudot et al. (2010) [10] in the 8000–9200 cm −1 spectral region) are used. This strongly suggests that the H 2O line strengths in the HITRAN-2008 database are indeed underestimated in this spectral region and in need of revision. The calculated global-mean clear-sky absorption of solar radiation is increased by about 0.3 W m −2 when using either the UCL08 or Oudot line parameters in the 8000–9200 cm −1 region, instead of HITRAN-2008. We also found that the effect of isotopic fractionation of HDO is evident in the 2500–2900 cm −1 region in the observations.

Spectroscopy and crystal-field analysis of Cr 4+-doped transparent silicate glass-ceramics

We report transparent Cr 4+-doped SiO 2–Al 2O 3–ZnO–Li 2O–K 2O glass-ceramics with broadband infrared luminescence. After heart-treatment, Li 2ZnSiO 4 crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. Racah parameters of Cr 4+–Li 2ZnSiO 4 glass-ceramics have been calculated, and it was confirmed from absorption spectra that the energy levels of Cr 4+-doped glass-ceramics are close to the cross point 1E and 3T states. No infrared emission was detected in the as-made glass samples, but the broadband infrared emission centered at 1210 nm with the full width at half maximum (FWHM) of more than 250 nm was observed by exciting the glass-ceramics with excitation of an 808 nm laser diode. In order to analyze the located crystal field of Cr 4+ ions, the emission spectra are fitted by multi-peak Gauss fitting. It is seen that the fluorescence spectra are fitted into two Gaussian bands at around 1195 and 1263 nm with band widths of 208 and 278 nm, respectively. The two Gaussian bands at around 1195 and 1263 nm have about the same decay rate, and hence they would probably originate from the same luminescent centers. The observed infrared emission could be attributed to Cr 4+ ions at low-field sites in Li 2ZnSiO 4 glass-ceramics.

Spectroscopic study of Cr^4+-doped transparent willemite nanocrystalline glass-ceramics

Cr4+-doped transparent β-Zn2SiO4 glass-ceramics were prepared by heat treatment on the as-made glasses. It was confirmed from the absorption spectra that Cr4+-doped β-Zn2SiO4 glass-ceramics are indeed a low-field system. The broadband infrared emission centering at 1342 nm with the full width at half-maximum of more than 285 nm was observed by exciting the glass-ceramics with the excitation of an 808 nm laser diode. The observed infrared emission could be attributed to Cr4+ ions at low-field sites in β-Zn2SiO4 glass-ceramics.

Broadband near-infrared emission from Cr 4+-doped transparent glass–ceramics based on lithium silicate

Cr 4+-doped transparent glass–ceramics containing Li 4SiO 4 nanocrystals were prepared by heat-treatment on as-made glasses. It was confirmed from absorption spectra that the energy levels of Cr 4+-doped the glass–ceramics is close to the cross point 1E and 3T states. The broadband infrared emission centered at 1230 nm with the full width at half maximum (FWHM) of more than 240 nm was observed by exciting the glass–ceramics with excitation of an 808 nm laser diode. The lifetime was about 230 μs at room temperature. The observed infrared emission could be attributed to Cr 4+ ions at low-field sites in Li 4SiO 4 glass–ceramics.

Composition dependence of the microspectroscopy of Cr ions in double-clad Cr:YAG crystal fiber

We have demonstrated the use of microspectroscopy for measuring the Cr3+ and Cr4+ fluorescence spectra in double-clad Cr:YAG crystal fiber. The emission spectra of Cr3+ and Cr4+ are detected from core and inner cladding. The Cr3+ spectrum in the inner cladding shows a broad-band emission from 650to950nm, while the emission of Cr4+ occurs in the range of 1.15–1.55μm with a peak around 1.22μm. The characteristic of Cr ion at high-field sites shows a narrow-band emission (E2→A24 for Cr3+; E1→A23 for Cr4+), whereas that at low-field sites shows a broad-band emission (T24→A24 for Cr3+; T23→A23 for Cr4+). The emission intensity ratio of high-field sites to low-field sites in the inner cladding with different compositions has been investigated. It varies from 20% to 29% for Cr3+ and from 7.1% to 11.3% for Cr4+ when the concentration of SiO2 increases from 26.9to43.0wt%.

Optical properties of single doped Cr3+ and co-doped Cr3+–Nd3+ aluminum tantalum tellurite glasses

The optical properties for single doped Cr3+ and co-doped Cr3+–Nd3+ aluminum tantalum tellurite glasses have been studied as a function of temperature. For the single doped glass, the existence of two bands in the emission spectra at low temperature indicates the presence of two different sites for the Cr3+ ions, labelled as usual as low- and high-field sites. The broad band centred in the Near Infrared region, corresponds to low-field sites transition 4T2→4A2, and the narrow band centred at approximately 715nm to the high-field sites transition 2E→4A2. The emission intensity for both high- and low-field sites shows a strong decrease with increasing temperature, with the emission for the former sites vanishing at RT. In both cases the quenching observed with the increase of temperature can be ascribed to the presence of non-radiative relaxation mechanisms. Experimental observations for the co-doped glass show that both radiative and non-radiative energy transfer processes from Cr3+ to Nd3+ are present.

Optical properties and site distribution of Cr 3+ ions in alkali-disilicate glasses

The optical properties of the low-field sites of Cr 3+-doped alkali (Li, Na, K) disilicate glasses have been investigated using the single configurational coordinate model. The assumption of a Gaussian site distribution for the Cr 3+ ions taking as parameter the zero-phonon energy has been considered. For alkali disilicate glasses the inhomogeneous contribution to the broadening of the bands, associated to the site distribution, is lower than the homogeneous one. The electron–lattice coupling S and the mean phonon energy ℏ ω 0 have been obtained with results around 4 and 500 cm −1, respectively, similar to those obtained by other authors in oxide glasses. The site-resolved study of the emission and excitation spectra and the luminescence decay curves have been carried out as a function of temperature. On the one hand, there is evidence of a non-radiative de-excitation process that becomes important over 140 K. On the other hand, and related to the site dependence of the radiative and non-radiative probabilities, different results involving low values for the quantum efficiencies and blue shifts of the emission bands as temperature increases have been explained. Besides, the non-exponential luminescence decay curves have been fitted to an expression proposed by the authors, which takes into account non-coupled distributions for the radiative and non-radiative de-excitation probabilities for the range of temperature covering from 13 to 300 K. From the fits, the temperature dependence of the non-radiative de-excitation probability is obtained for each disilicate glass, the results are in good agreement with the expression obtained assuming the harmonic approximation in the single configurational coordinate model.

Spectroscopy and crystal-field analysis for Cr(IV) in alumino-silicate glasses

Racah parameters of Cr4+ ions in alumino-silicate glasses have been calculated, indicating most Cr4+ ions are located at low-field sites. Using three-peak Gauss fitting for the luminescence lineshape of Cr4+:alumino-silicate glass at low temperatures, the existence of Cr4+ at high-field sites has been demonstrated for the first time in the alumino-silicate glass. The temperature dependence of the emission of low-Cr2O3 glass shows blue shift because most of the Cr4+ ions are in the low-field sites; in which the Cr4+ ions show the large difference of the thermal population at different excited states due to the non-radiative processes. On the other hand, the concentration dependence of the emission of Cr4+ ions in alumino-silicate glass shows red shift, caused by the energy transfer between Cr4+ ions in different crystal-field sites, and subsequently the mechanism of energy transfer between Cr4+ ions at low-field sites and at high-field sites has been proposed.

Field emission from chemical vapor deposition diamond surface with graphitic patches

The field emission properties of a polycrystalline diamond film with hydrogenated and hydrogen free surfaces have been investigated by monitoring both the emission current–voltage curve and emission site density. A very low turn-on field of electron emission was found to be 0.5 V/μm for the hydrogenated surface and 4 V/μm for the hydrogen free surface. The emission site densities were significantly reduced from 3×103 to 2×102 cm−2 at 5 V/μm after the surface hydrogen desorption. The low turn-on field and high emission site density on the hydrogenated surface are explained by the low work function of diamond combined with graphitic patches on the surface.

Inhomogeneous broadening ofCr3+luminescence in dopedLiTaO3

A theoretical model of the effect of inhomogeneous broadening on the luminescence lineshape of ${\mathrm{Cr}}^{3+}$ is developed and applied to the disordered system ${\mathrm{Cr}}^{3+}:{\mathrm{LiTaO}}_{3}.$ At ambient pressure, ${\mathrm{Cr}}^{3+}$ occupies primarily low-field sites in ${\mathrm{LiTaO}}_{3}$ and exhibits broad ${}^{4}{\stackrel{\ensuremath{\rightarrow}}{{T}_{2}}}^{4}{A}_{2}$ emission. The induction of a low-field $\ensuremath{\rightarrow}$ high-field transition with pressure led to the stabilization of narrow, well-resolved ${}^{2}{E}^{4}{A}_{2}$ emission and permitted us to determine that ${\mathrm{Cr}}^{3+}$ occupies two crystallographically distinct low-field sites at ambient pressure. These two sites were incorporated into a comprehensive electronic-structure model for ${\mathrm{Cr}}^{3+}$ that included the effects of spin-orbit and vibronic coupling to assess the influence of inhomogeneous broadening on the spectral lineshape. The model predicts that each of the two low-field sites is best described in terms of a Gaussian distribution of ${}^{4}{T}_{2}$ and ${}^{2}E$ energies. The model further indicates that the ${}^{4}{T}_{2}$ and ${}^{2}E$ energies within each Gaussian distribution are inversely correlated. The model successfully describes the emission lineshape, linewidth, and intensity of ${\mathrm{Cr}}^{3+}$ over a wide range of temperature and pressure, including during the low-field to high-field electronic transformation. A tentative molecular description of the different ${\mathrm{Cr}}^{3+}$ sites is also presented.