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Holmium Substitutes: What Can Replace Ho, and What Can't

Holmium (Ho) sits in a weird spot: it's used in a few applications where it's genuinely excellent (especially Ho:YAG medical lasers), and in several others where it's "one of a few ways" to achieve a performance target (flux concentrators, neutron absorbers, specialty magnetic materials, calibration standards).

The substitution reality in one sentence

Holmium is often substitutable at the system level (different laser platform, different absorber material, different calibration approach), but rarely substitutable as a simple one-to-one "swap Ho for X" without changing performance, workflow, qualification, or regulation.

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1) Medical lasers: Ho:YAG can be competed away, not trivially "replaced"

Substitute path A: Thulium fiber laser (TFL)

In urology (stone lithotripsy, and increasingly prostate work), TFL has become the most credible competitor to Ho:YAG. Comparative studies and meta-analyses generally frame TFL as at least comparable, with potential efficiency advantages in some settings, while noting that outcomes depend heavily on settings and technique.

What changes if a clinic shifts Ho:YAG → TFL:

  • Different consoles and fibers
  • Different parameter "sweet spots"
  • Training and preference cycles (slow-moving, but real)

Substitute path B: Pulsed thulium:YAG (p-Tm:YAG) in select workflows

Clinical and technical comparisons also treat pulsed thulium:YAG as a competitor that can outperform Ho:YAG on certain efficiency metrics, depending on settings and target outcomes.

Substitute path C: Redesign the procedure, not just the laser

Some "substitution" is changing technique (dusting vs fragmentation, basket use, anti-retropulsion strategy) to reduce the need for a specific laser performance envelope. That doesn't eliminate Ho demand, but it reduces the "Ho is mandatory" mindset.

Bottom line: Ho:YAG is still a reference platform in many places, but TFL and p-Tm:YAG are real substitution pressure, not a theoretical idea.

2) Holmium-166 therapies: the direct substitute is Yttrium-90

For radioembolization (TARE) using Ho-166 microspheres, the clearest substitute is Y-90 microspheres, which are already widely established. Multiple reviews explicitly position Ho-166 as an alternative to Y-90, which implies the reverse is also true: if Ho-166 availability or economics worsen, workflows can revert to Y-90.

Bottom line: This is one of the cleanest "A replaces B" holmium substitution cases in the real world.

3) High-field magnets and flux concentrators: substitute by changing the pole material or design

Holmium is used as a pole piece or flux concentrator in ultra-high-field magnet assemblies because of its cryogenic ferromagnetic behavior. This is documented in older high-field magnet work (holmium pole pieces adding several tesla of field enhancement).

Substitute path A: Dysprosium flux concentrators (cryogenic)

Dysprosium (Dy) is also used as a cryogenic pole-piece material / concentrator in high-field applications, including accelerator and insertion device contexts (textured Dy concentrators are an explicit development direction).

Substitute path B: Engineering substitution (geometry and alternative concentrators)

If Ho is constrained, teams can sometimes re-optimize the magnetic design (pole geometry, staged concentrators, different soft-magnetic approaches) rather than relying on a single rare-earth pole material.

Bottom line: This is substitutable, but only in engineering-led programs. It's not a procurement swap you do on a Friday afternoon.

4) Nuclear neutron absorption: use established absorber families instead of Ho

Holmium's neutron absorption makes it conceptually relevant, but mainstream reactor control and absorber practice already leans on well-established materials like boron carbide (B₄C) and hafnium.

The International Atomic Energy Agency documents absorber materials used in control assemblies (including B₄C and hafnium).

There's also a broader technical literature on burnable absorbers and absorber selection that reinforces the point: absorber choice is materials + neutronics + lifetime + manufacturability, not "pick the best cross-section element."

Bottom line: If any buyer truly needs to remove holmium from a neutron-absorber design, it's usually possible, but it requires design qualification and licensing discipline.

5) Optical wavelength calibration: you can substitute the standard, but you lose convenience

Holmium oxide glass is popular because it's compact, stable, and has well-characterized absorption bands.

Substitute path A: Didymium glass (a common alternative)

National Institute of Standards and Technology publications explicitly discuss both holmium oxide glass and didymium glass in wavelength calibration contexts, including caveats about slit-width dependence.

Substitute path B: Holmium oxide solution standards (same element, different format)

If the constraint is specifically holmium-glass availability (not holmium itself), a holmium-oxide-in-perchloric-acid solution can serve as an intrinsic wavelength standard, with certified absorption minima used for calibration.

Substitute path C: Emission lamps and other calibration methods

Alternative calibration approaches exist, but the trade-off is often practicality (setup, alignment, lamp aging) versus the "drop-in filter" convenience that made holmium glass dominant in many labs.

Bottom line: You can substitute the calibration standard, but the reason people keep using holmium glass is that it's stable and operationally easy.

6) Holmium in magnets and specialty magnetic materials: substitution is usually a design decision

Holmium can appear in magnet and magnetic-material R&D as part of the broader "heavy rare earth tuning" toolbox. In Nd-Fe-B magnets, literature notes that holmium could substitute for part of dysprosium in some magnet designs (same function class: coercivity tuning, temperature behavior), which implies interchangeability among heavy-REE strategies depending on availability and performance targets.

If the goal is "avoid holmium," practical options usually look like:

  • Use a different heavy rare earth (often Dy/Tb strategies where appropriate)
  • Reduce heavy-REE needs via microstructure engineering and process improvements
  • Accept performance trade-offs

Bottom line: This is substitutable, but it's not a commodity-like switch. It's magnet engineering.

Holmium Substitutes FAQ

1) Is TFL a true replacement for Ho:YAG in urology?

It can be, depending on the procedure and settings. The literature increasingly treats TFL as a credible competitor with potential efficiency advantages, but outcomes are technique- and parameter-dependent. The shift from Ho:YAG to TFL is not a simple equipment swap; it involves new consoles, fibers, parameter optimization, and clinician training. In practice, TFL competes with Ho:YAG rather than replacing it on a one-to-one basis.

2) If holmium glass filters are unavailable, what's the next-best calibration substitute?

Didymium glass is a common alternative for wavelength checks, but users still need to respect instrument slit-width effects and calibration conditions. Another option is holmium oxide solution standards (same element, different format), which provide certified absorption minima. Emission lamps and other calibration methods also exist, but they trade the convenience of drop-in filters for more complex setup requirements.

3) What's the simplest substitute for holmium as a neutron absorber?

In practical reactor hardware, boron carbide (B₄C) and hafnium are established absorber materials with deep qualification history, which is why they tend to be the default substitutes. The choice involves more than just neutron cross-section; it includes materials compatibility, lifetime performance, manufacturability, and regulatory qualification. Switching absorber materials is technically feasible but requires design requalification and licensing updates.

4) Can dysprosium fully replace holmium in high-field magnet pole pieces?

Dysprosium can serve as a cryogenic flux concentrator in similar applications, but substitution is not plug-and-play. The magnetic properties, temperature behavior, and engineering integration differ. Substituting Dy for Ho in high-field magnet assemblies typically requires redesign and requalification of the magnetic circuit. This is feasible in engineering-led programs but not a simple procurement swap.

5) Is Y-90 always better than Ho-166 for radioembolization?

Not necessarily better, but more established. Y-90 has been used in radioembolization (TARE) for decades and has extensive clinical evidence and regulatory approval. Ho-166 offers some advantages, including the ability to visualize distribution using SPECT imaging due to its gamma emissions, but it is less widely available. If Ho-166 supply becomes constrained, most clinical workflows can revert to Y-90 without fundamental changes to the therapeutic approach.

6) Can holmium be avoided entirely in Nd-Fe-B magnets?

Yes. Holmium is not a mainstream heavy rare earth in commercial Nd-Fe-B magnets. When it does appear, it's typically in research or niche applications exploring alternative heavy-REE tuning strategies. Dysprosium and terbium are the standard heavy rare earths for coercivity enhancement. If holmium were to become unavailable, magnet manufacturers could continue using established Dy/Tb approaches or pursue grain-boundary engineering strategies to reduce heavy-REE dependence altogether.

Key Takeaways: The Substitution Landscape

System-level substitution is real

Most holmium applications can be addressed through alternative technologies, materials, or design approaches. The substitution is rarely a simple material swap but rather a system redesign (different laser type, different absorber material, different calibration method).

Substitution carries transition costs

Even when technical substitutes exist, the transition involves costs: capital equipment replacement, requalification testing, regulatory approval, supply chain restructuring, and retraining. These costs can be substantial enough to keep existing holmium-based solutions in place even when alternatives are available.

Inertia matters as much as technology

In many cases, holmium continues to be used not because substitutes don't exist, but because the installed base, qualification history, and operational familiarity create strong inertia. Substitution pressure increases only when supply constraints, price volatility, or performance advantages become compelling enough to justify the transition investment.