BET surface area

Specific surface area measured using gas adsorption. Useful for comparing powder surface area and, indirectly, fineness/agglomeration behavior.

COA

Certificate of Analysis — lot-specific evidence of selected test results against a specification.

D10 / D50 / D90

Percentile particle-size values. D50 is the median; D90 means 90% of the measured distribution is below that size.

Gadolinia

Common name for gadolinium(III) oxide, Gd₂O₃.

High-k

A dielectric material with a relatively high dielectric constant compared with SiO₂; used in advanced electronic-material research.

LOI

Loss on ignition — mass lost under defined heating conditions, often related to moisture, carbonates or other volatile species.

REO basis

Purity calculated relative to total rare-earth oxides. Non-rare-earth impurities may be reported separately.

3N / 4N / 5N

Shorthand for nominal 99.9%, 99.99% and 99.999% purity.

Neutron capture cross section

A probability-like measure expressed in barns that describes the likelihood of neutron interaction at a specified energy. ¹⁵⁵Gd and ¹⁵⁷Gd are notable thermal-neutron absorbers.

Phosphor host

A material lattice that contains optically active dopant ions and supports luminescent emission after excitation.

ALD

Atomic Layer Deposition, a cyclic thin-film deposition technique capable of highly conformal, controlled film growth.

Primary particle vs agglomerate

Primary particles are the underlying small particles/crystallites; agglomerates are clusters. Many “nano” powders measure much larger when dispersed poorly.