If a bull market emerges in 2023, prospective investors in dividend stocks will be in a race against time to buy shares while prices are low and dividend yields are high. After a run-up, such companies might not be priced at a bargain anymore, and that means you might be better off waiting for shares to fall once more, losing valuable time to be accumulating dividends in the process.

With that in mind, let's analyze a couple of passive income stocks. One of the pair is ripe for a purchase today, but the other is a tempting trap. Here's why. 

1. Alexandria Real Estate Equities

Alexandria Real Estate Equities (ARE 0.95%) is a dividend stock that's worth buying soon as a long-term hold to generate a ton of passive income. The company specializes in leasing biomedical laboratory spaces, which it builds out in cities like Boston that are hubs for scientific research and global healthcare businesses.

Its tenants include a handful of major biomedical businesses that you've likely heard of, including such heavyweights as Pfizer and Moderna. That means its tenants can be counted on to pay rent for year after year without incident, making its returns fairly safe for investors. 

At the moment, its forward dividend yield is a bit over 3.3%, and over the last five years, its payout grew by 34.4%. In the same period, its trailing 12-month cash from operations rose by 153.4%, reaching above $1.1 billion. That suggests its strategy has enduring traction with its prospective renters, as does its occupancy rate of 94.3% in the third quarter.

It also suggests that when a bull market makes it more appealing for smaller biomedical players to issue new stock to raise capital, there will be an uptick in the number of companies looking to rent space from Alexandria. If that happens, people who bought the stock early will see a nice gain.

Alexandria is well-positioned to keep expanding its footprint of facilities (and its bottom line), despite headwinds like inflation and rising interest rates. It has more than $533 million in cash and equivalents to spend on acquisitions, and its total debt load of around $10.9 billion isn't very large in comparison to its market capitalization of around $23.7 billion.

Plus, its credit rating is in the top decile of all public real estate investment trusts (REITs) in the U.S. So it shouldn't have a hard time borrowing at an attractive rate to get even more cash to grow, should the need arise. In sum, there's little in the way of red flags with Alexandria, and as long as the biomedical sector keeps growing, it'll continue to have enough capital to hike its dividend while expanding in the long term.

2. Medical Properties Trust

Like Alexandria Real Estate, Medical Properties Trust (MPW) is a REIT, but its target tenants are hospitals and clinics, in which it also sometimes makes direct investments. But the similarities start to end there. Rather than growing consistently year over year, its trailing 12-month cash from operations fell by 2.4% over the past four quarters to just over $792 million, and there's reason to believe its pace of expansion might slow further.

The No. 1 problem is that its target tenants aren't experiencing much growth in any way that will consistently benefit Medical Properties Trust. After all, demand for new hospitals is unlikely to be very high in the long term in the U.S., especially if population growth isn't high and existing hospitals continue to be roughly as efficient at using their floorspace as in the past.

Remember, healthcare expenditures can easily continue to increase quite quickly, but it takes the same amount of physical space to administer a cheap generic drug as it does to administer the pricey branded version of the same drug, so rising expenditures are not in and of themselves a positive sign for future hospital floor space demand.

Growth problems aside, the business is unlikely to be able to return much more capital to investors in the near future than it does today. Its forward dividend yield is nearly 10%, which is tantalizingly high. But its dividend only grew by a paltry 16% in the last five years, and the ratio of its total debt to its market cap is more than twice as high as Alexandria's. That means its approximately $9.5 billion in total debt is a proportionally larger burden when it comes to the cost of borrowing capital to fund the purchase of new properties to rent out. 

Overall, MPT isn't as attractive an investment as Alexandria, and that might not change anytime soon. Nonetheless, if it can reduce its debt burden significantly, it could potentially become a competitive choice, though it'll need to work on that goal for several years before it's a draw to investors.